[Haskell-cafe] Statically tracking validity - suggestions?
Hello. I'm using Haskell to write a specification for some software. The
software uses certificates (standard X.509 certificates) and stores user
name information in the Subject's CommonName field.
The X.509 standard doesn't actually require the presence of a CommonName
field so the contents of the Subject section (with the rest of the fields
omitted) are just represented by a Maybe User_Name.
import Data.List (find, concat)
import Data.Maybe (fromJust, isJust)
type User_Name= String
type Public_Key = Integer
data Subject_Name = Subject_Name (Maybe User_Name) deriving (Show, Eq)
data Certificate = Certificate {
certificate_subject :: Subject_Name,
certificate_key :: Public_Key,
certificate_issuer :: String,
certificate_serial :: Integer
} deriving (Show, Eq)
This is all well and good, but the problem is that the validity of
certificates isn't tracked statically and I have to use the following
as guards on all functions that only expect valid certificates (and
inevitably handle cases that I know can't actually happen but
have to be handled in pattern matching and the like, bloating
the specification):
user_name :: Subject_Name - Maybe User_Name
user_name (Subject_Name name) = name
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
I'm aware of phantom types and the like, but I've been unable to
work out how to use them (or another type system extension)
to properly track validity on the type level. I'd want something
like:
validate :: Certificate Possibly_Valid - Maybe (Certificate Valid)
With later functions only accepting values of type Certificate Valid.
Is there a simple way to do this?
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Re: [Haskell-cafe] Statically tracking validity - suggestions?
On 31 aug 2010, at 08:24, strejon wrote:
Hello. I'm using Haskell to write a specification for some software. The
software uses certificates (standard X.509 certificates) and stores user
name information in the Subject's CommonName field.
The X.509 standard doesn't actually require the presence of a CommonName
field so the contents of the Subject section (with the rest of the fields
omitted) are just represented by a Maybe User_Name.
import Data.List (find, concat)
import Data.Maybe (fromJust, isJust)
type User_Name= String
type Public_Key = Integer
data Subject_Name = Subject_Name (Maybe User_Name) deriving (Show, Eq)
data Certificate = Certificate {
certificate_subject :: Subject_Name,
certificate_key :: Public_Key,
certificate_issuer :: String,
certificate_serial :: Integer
} deriving (Show, Eq)
This is all well and good, but the problem is that the validity of
certificates isn't tracked statically and I have to use the following
as guards on all functions that only expect valid certificates (and
inevitably handle cases that I know can't actually happen but
have to be handled in pattern matching and the like, bloating
the specification):
user_name :: Subject_Name - Maybe User_Name
user_name (Subject_Name name) = name
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
I'm aware of phantom types and the like, but I've been unable to
work out how to use them (or another type system extension)
to properly track validity on the type level. I'd want something
like:
validate :: Certificate Possibly_Valid - Maybe (Certificate Valid)
With later functions only accepting values of type Certificate Valid.
Is there a simple way to do this?
Yes. Introduce a wrapper datatype, ValidCertificate. Create a module and export
only the wrapper datatype and a way to construct ValidCertificates in a safe
way:
module ValidateCertificate
( ValidCertificate,
fromValidCertificate,
createValidCertificate
) where
data ValidCertificate = ValidCertificate {fromValidCertificate :: Certificate}
createValidCertificate :: Certificate - Maybe ValidCertificate
createValidCertificate c | is_valid c = Just (ValidCertificate c)
| otherwise = Nothing
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
The trick is not to export the constructor, but only a verified way to
construct values of ValidCertificate.
-chris___
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Re: [Haskell-cafe] Statically tracking validity - suggestions?
On Tue, Aug 31, 2010 at 08:24, strejon strej...@yahoo.com wrote:
Hello. I'm using Haskell to write a specification for some software. The
software uses certificates (standard X.509 certificates) and stores user
name information in the Subject's CommonName field.
The X.509 standard doesn't actually require the presence of a CommonName
field so the contents of the Subject section (with the rest of the fields
omitted) are just represented by a Maybe User_Name.
import Data.List (find, concat)
import Data.Maybe (fromJust, isJust)
type User_Name = String
type Public_Key = Integer
data Subject_Name = Subject_Name (Maybe User_Name) deriving (Show, Eq)
data Certificate = Certificate {
certificate_subject :: Subject_Name,
certificate_key :: Public_Key,
certificate_issuer :: String,
certificate_serial :: Integer
} deriving (Show, Eq)
This is all well and good, but the problem is that the validity of
certificates isn't tracked statically and I have to use the following
as guards on all functions that only expect valid certificates (and
inevitably handle cases that I know can't actually happen but
have to be handled in pattern matching and the like, bloating
the specification):
user_name :: Subject_Name - Maybe User_Name
user_name (Subject_Name name) = name
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
I'm aware of phantom types and the like, but I've been unable to
work out how to use them (or another type system extension)
to properly track validity on the type level. I'd want something
like:
validate :: Certificate Possibly_Valid - Maybe (Certificate Valid)
With later functions only accepting values of type Certificate Valid.
Is there a simple way to do this?
If you want to use types instead of modules and hiding as Chris
suggested, you can use a type index like this:
{-# LANGUAGE EmptyDataDecls, GADTs, KindSignatures #-}
data Nothing
data Just a
data Subject :: * - * where
NoName :: Subject Nothing
Name :: String - Subject (Just String)
data Certificate a = Certificate
{ subject :: Subject a }
validate :: Certificate a - Maybe (Certificate (Just String))
validate c =
case subject c of
NoName - Nothing
Name n - Just c
A Certificate (Just String) now always holds a name, and a
Certificate Nothing doesn't. A Certificate a can hold either.
Erik
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Re: [Haskell-cafe] open and closed
On Mon, Aug 30, 2010 at 1:23 PM, wren ng thornton w...@freegeek.org wrote: On 8/29/10 1:33 PM, Gábor Lehel wrote: Another thing I'm wondering about is that there's a fairly intuitive correspondence between functions at the value level vs. functions at the type level, and datatypes to classify the value level vs. datakinds to classify the type level, but what corresponds to type classes at the value level? Wouldn't you go the other way: kind classes? Type classes are predicates on types, and the application of a class to a type forms a proposition which represents the type of proofs that the proposition holds (i.e., the type of instance dictionaries). This can be easily extended upwards by having predicates on kinds yielding propositions that represent the kinds of (type-level) proofs. IIRC, this is the perspective that Omega takes. To extend it downward we'd have to ask what it would mean to have a predicate on values. The value-level propositions formed by applying those predicates couldn't have proofs (because there is no sub-value level), so it's not entirely clear what that would mean. If anything, the value-level correspondent of type classes are just uninterpreted predicates, i.e. data constructors. Whether this line of thinking is sensible or just a fallacious attempt to unify everything, I can't say off hand. I think it's better to think of contexts as the type of the invisible lambda for passing dictionaries, just as forall is the type of (the invisible) big-lambda, and - is the type of lambda. Thus, the dictionaries are the concrete thing you want to generalize to higher levels; the classes will be at the next level up. Hmm, I see. I think what had me confused was that type classes seem to be at the same level as types, and, like functions, to interact with things at their own level; but then they also interact with something from one level lower (instance dictionaries), which is why it doesn't make sense to transplant them to the lowest level (values). Thanks for the explanation! -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Work is punishment for failing to procrastinate effectively. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Statically tracking validity - suggestions?
Erik Hesselink wrote:
If you want to use types instead of modules and hiding as Chris
suggested, you can use a type index like this:
{-# LANGUAGE EmptyDataDecls, GADTs, KindSignatures #-}
data Nothing
data Just a
data Subject :: * - * where
NoName :: Subject Nothing
Name :: String - Subject (Just String)
data Certificate a = Certificate
{ subject :: Subject a }
validate :: Certificate a - Maybe (Certificate (Just String))
validate c =
case subject c of
NoName - Nothing
Name n - Just c
A Certificate (Just String) now always holds a name, and a
Certificate Nothing doesn't. A Certificate a can hold either.
Erik
Thanks, both of you. The GADT version seems slightly easier
to work with in our case.
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Re: [Haskell-cafe] Statically tracking validity - suggestions?
I have a description of the design pattern you need, appropriately
named: http://lukepalmer.wordpress.com/2009/03/24/certificate-design-pattern/
On Tue, Aug 31, 2010 at 12:24 AM, strejon strej...@yahoo.com wrote:
Hello. I'm using Haskell to write a specification for some software. The
software uses certificates (standard X.509 certificates) and stores user
name information in the Subject's CommonName field.
The X.509 standard doesn't actually require the presence of a CommonName
field so the contents of the Subject section (with the rest of the fields
omitted) are just represented by a Maybe User_Name.
import Data.List (find, concat)
import Data.Maybe (fromJust, isJust)
type User_Name = String
type Public_Key = Integer
data Subject_Name = Subject_Name (Maybe User_Name) deriving (Show, Eq)
data Certificate = Certificate {
certificate_subject :: Subject_Name,
certificate_key :: Public_Key,
certificate_issuer :: String,
certificate_serial :: Integer
} deriving (Show, Eq)
This is all well and good, but the problem is that the validity of
certificates isn't tracked statically and I have to use the following
as guards on all functions that only expect valid certificates (and
inevitably handle cases that I know can't actually happen but
have to be handled in pattern matching and the like, bloating
the specification):
user_name :: Subject_Name - Maybe User_Name
user_name (Subject_Name name) = name
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
I'm aware of phantom types and the like, but I've been unable to
work out how to use them (or another type system extension)
to properly track validity on the type level. I'd want something
like:
validate :: Certificate Possibly_Valid - Maybe (Certificate Valid)
With later functions only accepting values of type Certificate Valid.
Is there a simple way to do this?
--
View this message in context:
http://old.nabble.com/Statically-tracking-%22validity%22---suggestions--tp29579872p29579872.html
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Re: [Haskell-cafe] Quick Question for QuickCheck2
ghc-pkg check doesn't list any broken dependencies. On Tue, Aug 31, 2010 at 9:27 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 31 August 2010 03:18, Lyndon Maydwell maydw...@gmail.com wrote: Thanks! This makes perfect sense, but as I just discovered using ghci -v there is an even stranger problem. I'm side-tracking slightly from the original question here, but nevertheless... GHC gives the following output: --- GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help command line: cannot satisfy -package QuickCheck-2.1.1.1: QuickCheck-2.1.1.1-c7435cb0d5b5de72fe9540c48335606d is unusable due to missing or recursive dependencies: ghc-6.12.3-66a382195c8a71849653439b67021fd1 (use -v for more information) shell returned 1 What does ghc-pkg check say? To me, it sounds like you upgraded a boot library, which is a big no-no. (The ghc mentioned here is the ghc library, not the compiler itself.) -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Slightly humorous: Headhunters toolbox (example for Germany)
On Sat, 28 Aug 2010 00:45:23 +0200, sylvain sylvain.na...@googlemail.com wrote: Apart the programming language, I have encountered this term only as a family name. I would find interesting to know if there is a language in which this word exists and has yet another meaning. It is amongst others the name of a city in Arkansas, several counties in the USA, the first name of Haskell B. Curry and it occurs in the name of shops, like Haskell's . There are several street names, like Haskell Street, Haskell Lane, Haskell Avenue. Try Google earth, it list nine locations with Haskell in the name. Furthermore, there are the Haskell Free Library and Opera House, the Haskell Indian Nations University, the Haskell Invitational Handicap and the Haskell Oriental Museum. Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quick Question for QuickCheck2
On 31 August 2010 20:38, Lyndon Maydwell maydw...@gmail.com wrote: ghc-pkg check doesn't list any broken dependencies. You sure this is with the same user? ghci is unlikely to complain about broken libraries if ghc-pkg check doesn't... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: iteratee-compress 0.1
Iteratee-compress provides compressing and decompressing enumerators. Currently only gzip is provided but at least bzip is planned. Additionally more fine-control over stream (i.e. flushing) is planned. Library currently depends on zlib haskell library only for sharing parameters data. However no zlib function is called (the needed functions are not exported) and the symbols it uses from necessity are deprecated. Would it be better to copy the parameters from zlib and drop the dependency? Please note also that the library do not bundle zlib (C) as zlib (Haskell) do. signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quick Question for QuickCheck2
Yep. Definitely the same user. On Tue, Aug 31, 2010 at 7:35 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 31 August 2010 20:38, Lyndon Maydwell maydw...@gmail.com wrote: ghc-pkg check doesn't list any broken dependencies. You sure this is with the same user? ghci is unlikely to complain about broken libraries if ghc-pkg check doesn't... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] :Trace has no history
I am trying to debug a problem in GHCI. I invoke my method with trace but when it breaks on exception i can't get this history. Output is below. Thanks. relude Symbols :set -fbreak-on-exception Prelude Symbols :trace myMethod Loading package HUnit-1.2.2.1 ... linking ... done. Loading package syb-0.1.0.2 ... linking ... done. Loading package base-3.0.3.2 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package Decimal-0.1.0 ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package Diff-0.1.2 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package convertible-1.0.9 ... linking ... done. Loading package utf8-string-0.3.4 ... linking ... done. Loading package HDBC-2.2.6 ... linking ... done. Loading package HDBC-mysql-0.6.3 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.1.7 ... linking ... done. Loading package HTTP-4000.0.9 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package digest-0.0.0.8 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package unix-2.4.0.0 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package zlib-0.5.2.0 ... linking ... done. Loading package zip-archive-0.1.1.6 ... linking ... done. Loading package Core-0.0.1 ... linking ... done. Beginning Update Stopped at exception thrown _exception :: e = GHC.Exception.SomeException (GHC.Exception.D:Exception _ (GHC.Show.D:Show ...) ) (GHC.IO.Exception.IOError Nothing GHC.IO.Exception.UserError ) [exception thrown] Prelude Symbols :history Empty history. Perhaps you forgot to use :trace? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Searching for Haskell (was: [Haskell-cafe] Slightly humorous: Headhunters toolbox (example for Germany))
On Tue, 31 Aug 2010 13:57:42 +0200, Alberto G. Corona agocor...@gmail.com wrote: Entering haskell language instead of haskell the ambiguity dissapears. Then, Jamaica no longer appears in the crude reality . The weigth of USA is hides all other country here. I think that a more appropriate term to look for haskell interest is monad although it may catch some crazy philosophers too. The result is interesting, You can still get things like a page titled Ben Haskell - Language Technologies Institute - Carnegie Mellon, and of course, not all pages about the programming language contain the word language. To get proper results you would need a good semantic search engine, but these search engines seem to be in early research stage. Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Slightly humorous: Headhunters toolbox (example for Germany)
On Sat, 28 Aug 2010 00:45:23 +0200, sylvain sylvain.na...@googlemail.com wrote: Apart the programming language, I have encountered this term only as a family name. I would find interesting to know if there is a language in which this word exists and has yet another meaning. It is amongst others the name of a city in Arkansas, several counties in the USA, the first name of Haskell B. Curry and it occurs in the name of shops, like Haskell's . There are several street names, like Haskell Street, Haskell Lane, Haskell Avenue. Try Google earth, it list nine locations with Haskell in the name. Furthermore, there are the Haskell Free Library and Opera House, the Haskell Indian Nations University, the Haskell Invitational Handicap and the Haskell Oriental Museum. Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quick Question for QuickCheck2
Do you have ~/.cabal/bin/ in your PATH? - Sebastian Am 31.08.2010 um 15:57 schrieb Lyndon Maydwell: Yep. Definitely the same user. On Tue, Aug 31, 2010 at 7:35 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 31 August 2010 20:38, Lyndon Maydwell maydw...@gmail.com wrote: ghc-pkg check doesn't list any broken dependencies. You sure this is with the same user? ghci is unlikely to complain about broken libraries if ghc-pkg check doesn't... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] On to applicative
Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
So it's a type constructor, not a type? Could you please provide a simple example of its usage? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quick Question for QuickCheck2
Yep :) Is there a batch of information that might be useful? I can send any relevant files, aliases, versions, etc at once to help if you like. On Wed, Sep 1, 2010 at 12:35 AM, Sebastian Höhn sebastian.ho...@iig.uni-freiburg.de wrote: Do you have ~/.cabal/bin/ in your PATH? - Sebastian Am 31.08.2010 um 15:57 schrieb Lyndon Maydwell: Yep. Definitely the same user. On Tue, Aug 31, 2010 at 7:35 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 31 August 2010 20:38, Lyndon Maydwell maydw...@gmail.com wrote: ghc-pkg check doesn't list any broken dependencies. You sure this is with the same user? ghci is unlikely to complain about broken libraries if ghc-pkg check doesn't... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] On to applicative
Hello michael, Tuesday, August 31, 2010, 9:27:17 PM, you wrote: f :: Int - Int i.e. it's used when you define function types So it's a type constructor, not a type? Could you please provide a simple example of its usage? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Fwd: Searching for Haskell (was: [Haskell-cafe] Slightly humorous: Headhunters toolbox (example for Germany))
Ooops Just after sending this I relized that it is possible to narrow the search using categories. Using the category programming: http://www.google.com/insights/search/?hl=en-US#cat=31q=haskellcmpt=q http://www.google.com/insights/search/?hl=en-US#cat=31q=haskellcmpt=qit is even possible to compare the evolution of the term against the whole category. Both go down with time (because technical people dominate less and less the wen searches) . But the slope of Haskell is lesser than the one of programming. By the way, it is possible to compare two or more search terms. Within the category programming, monad, and type class are scarce compared with object but the slope of the former ones are clearly up while object is down. (press growth compared with the programing category). What happened in the first half of 2006? monads were high there!. An further example is lazy versus strict. Both are comparable in percentage, but lazy is scandalously up while strict is down at the same rate. http://www.google.com/insights/search/?hl=en-US#cat=31q=lazy%2Cstrict%2Ccmpt=q By the way, the term tired has increasing share in the programming category ;) 2010/8/31 Henk-Jan van Tuyl hjgt...@chello.nl On Tue, 31 Aug 2010 13:57:42 +0200, Alberto G. Corona agocor...@gmail.com wrote: Entering haskell language instead of haskell the ambiguity dissapears. Then, Jamaica no longer appears in the crude reality . The weigth of USA is hides all other country here. I think that a more appropriate term to look for haskell interest is monad although it may catch some crazy philosophers too. The result is interesting, You can still get things like a page titled Ben Haskell - Language Technologies Institute - Carnegie Mellon, and of course, not all pages about the programming language contain the word language. To get proper results you would need a good semantic search engine, but these search engines seem to be in early research stage. Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] :Trace has no history
Hi Steve The debugger only traces calls in interpreted code. Perhaps the call to myMethod is being made from object code? Admittedly, the ghci debugger can take some effort to learn to use properly. Make sure that you give a look to the ghc user guide if you haven't done so yet. Best, pepe On Tuesday, August 31, 2010, Steve sseve...@gmail.com wrote: I am trying to debug a problem in GHCI. I invoke my method with trace but when it breaks on exception i can't get this history. Output is below. Thanks. relude Symbols :set -fbreak-on-exception Prelude Symbols :trace myMethod Loading package HUnit-1.2.2.1 ... linking ... done. Loading package syb-0.1.0.2 ... linking ... done. Loading package base-3.0.3.2 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package Decimal-0.1.0 ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package Diff-0.1.2 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package convertible-1.0.9 ... linking ... done. Loading package utf8-string-0.3.4 ... linking ... done. Loading package HDBC-2.2.6 ... linking ... done. Loading package HDBC-mysql-0.6.3 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.1.7 ... linking ... done. Loading package HTTP-4000.0.9 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package digest-0.0.0.8 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package unix-2.4.0.0 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package zlib-0.5.2.0 ... linking ... done. Loading package zip-archive-0.1.1.6 ... linking ... done. Loading package Core-0.0.1 ... linking ... done. Beginning Update Stopped at exception thrown _exception :: e = GHC.Exception.SomeException (GHC.Exception.D:Exception _ (GHC.Show.D:Show ...) ) (GHC.IO.Exception.IOError Nothing GHC.IO.Exception.UserError ) [exception thrown] Prelude Symbols :history Empty history. Perhaps you forgot to use :trace? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- -- José Iborrahttp://www.dsic.upv.es/~jiborra -- UPV Valencia Telf. (+34) 96 387 00 00 (ext) 83529 -- Camino de Vera s/n. 46022 Valencia (Spain) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Arrow transformers: how to make them wright?
A Control.Arrow in base package introduces an arrow type, and ghc have good support for arrow notation. Many things, avaible in monads, are avaible in arrows as well. There is an arrows package, that introduces some arrow classes : state, reader, writer and so on. However, it does not introduce systematic lifting of arrow classes operations. Arrows are generalisation of monads. There are libraries, that introduces systematic lifting of operations from monad classes. So, the quesions are: what operations should be in arrow transformer class? Captain Obvious says, it should look at least like: class ArrowTrans t where lift :: ( Arrow a, Arrow (t a) ) = a b c - t a b c what laws arrow transformers must obey? C.O. says, at least lift a b c lift a c d == lift ( a b c a c d ) how to perform lifting of actions for classes like this: class Arrow a = ArrowError a e| a- e where raise :: a e () handle :: a e c - a b c - a b c class Arrow a = ArrowReader a e | a - e where look :: a () e local :: a b c - a (b,e) c The answers lies somewhere in category theory, C.O. says. Of course, such answer is not satisfactory. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Arrow transformers: how to make them wright?
Hello Permjacov, Tuesday, August 31, 2010, 10:07:38 PM, you wrote: what operations should be in arrow transformer class? oh, these Russians :) -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Statically tracking validity - suggestions?
Luke Palmer wrote: I have a description of the design pattern you need, appropriately named: http://lukepalmer.wordpress.com/2009/03/24/certificate-design-pattern/ Mmm, I like that. There are two small problems: * In my web browser, some of the code snippets get the right-hand edge chopped off. * Double-precision floating-point arithmetic is inexact, so half your code won't actually work in the real world. (But obviously, it's only supposed to be an example for illustration purposes.) With regard to the second, does anybody know of anything on Hackage for testing whether two values are approximately equal? It must be a common programming problem, and it's more tricky than you think to solve it well. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Statically tracking validity - suggestions?
2010/8/31 Andrew Coppin andrewcop...@btinternet.com: Luke Palmer wrote: I have a description of the design pattern you need, appropriately named: http://lukepalmer.wordpress.com/2009/03/24/certificate-design-pattern/ Mmm, I like that. There are two small problems: * In my web browser, some of the code snippets get the right-hand edge chopped off. * Double-precision floating-point arithmetic is inexact, so half your code won't actually work in the real world. (But obviously, it's only supposed to be an example for illustration purposes.) With regard to the second, does anybody know of anything on Hackage for testing whether two values are approximately equal? It must be a common programming problem, and it's more tricky than you think to solve it well. I think something has been added to Hackage recently about that. There is this one, but I don't know if it is the one I was thinking about. http://hackage.haskell.org/package/ieee Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On *Tue, 8/31/10, Vo Minh Thu not...@gmail.com* wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.comhttp://mc/compose?to=not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.comhttp://mc/compose?to=not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com Cc: haskell-cafe@haskell.orghttp://mc/compose?to=haskell-c...@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Arrow transformers: how to make them wright?
On Tue, Aug 31, 2010 at 2:07 PM, Permjacov Evgeniy permea...@gmail.com wrote: A Control.Arrow in base package introduces an arrow type, and ghc have good support for arrow notation. Many things, avaible in monads, are avaible in arrows as well. There is an arrows package, that introduces some arrow classes : state, reader, writer and so on. However, it does not introduce systematic lifting of arrow classes operations. Are you referring to the arrows package at http://hackage.haskell.org/package/arrows? If so, what do you mean by systematic lifting, because it does lift operations through the transformers where possible. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
2010/8/31 michael rice nowg...@yahoo.com I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer We say that m has type Maybe Integer, so :: is pronounced 'has type'. We also say that m is a value. Just is a type constructor, Maybe Int is a type, and Just 7, like m, is a value. So we don't talk about instance here. Informally you could say that 7 is an instance of Int, but in Haskell we use 'instance' to mean something (precisely) else. This pharse is correct w.r.t to the use of 'instance' in Haskell: Maybe is an instance of the Functor class. Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Note that for Maybe, the instance is define with instance Functor Maybe where ... Note how the type argument of Maybe is not given. But above, when you create a value, it has type Maybe Int, not only Maybe. So for the ((-) r) case, you still want to complete it. E.g. m :: Maybe Int -- not just Maybe (+) :: (-) Int Int -- and not only (-) Int Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
2010/8/31 michael rice nowg...@yahoo.com Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' :t Int does not make sense but :t undefined :: Int is ok, just like :t undefined :: (-) Int Int What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Hi Vo, Pardon, I grabbed the wrong lines. *Main :t (-) 3 abc interactive:1:1: parse error on input `-' Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Ryan Ingram ryani.s...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 3:07 PM 2010/8/31 michael rice nowg...@yahoo.com Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' :t Int does not make sense but :t undefined :: Int is ok, just like :t undefined :: (-) Int Int What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
2010/8/31 michael rice nowg...@yahoo.com Hi Vo, Pardon, I grabbed the wrong lines. *Main :t (-) 3 abc interactive:1:1: parse error on input `-' Try *Main :t undefined :: (-) 3 abc You can't write :t some type You have to write :t some value Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Ryan Ingram ryani.s...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 3:07 PM 2010/8/31 michael rice nowg...@yahoo.com Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' :t Int does not make sense but :t undefined :: Int is ok, just like :t undefined :: (-) Int Int What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
On Aug 31, 2010, at 12:03 PM, michael rice wrote: I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' Try: Prelude :info (-) data (-) a b-- Defined in GHC.Prim If you want type-information about values, use :t. If you want information about types (and the type-level language), use :info. This includes stuff like class definitions and instances in scope. For example, if I include Control.Monad: Prelude Control.Monad.Instances :info (-) data (-) a b-- Defined in GHC.Prim instance Monad ((-) r) -- Defined in Control.Monad.Instances instance Functor ((-) r) -- Defined in Control.Monad.Instances :info is pretty cool: Prelude Control.Monad.Instances :info Monad class Monad m where (=) :: m a - (a - m b) - m b () :: m a - m b - m b return :: a - m a fail :: String - m a -- Defined in GHC.Base instance Monad ((-) r) -- Defined in Control.Monad.Instances instance Monad Maybe -- Defined in Data.Maybe instance Monad [] -- Defined in GHC.Base instance Monad IO -- Defined in GHC.Base ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: iteratee-compress 0.1
On Tue, Aug 31, 2010 at 6:51 AM, Maciej Piechotka uzytkown...@gmail.com wrote: Iteratee-compress provides compressing and decompressing enumerators. Currently only gzip is provided but at least bzip is planned. Additionally more fine-control over stream (i.e. flushing) is planned. Library currently depends on zlib haskell library only for sharing parameters data. However no zlib function is called (the needed functions are not exported) and the symbols it uses from necessity are deprecated. Would it be better to copy the parameters from zlib and drop the dependency? I'd prefer to see you add zlib support and keep the dependency :) Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fourth (and Fifth) GhentFPG Meeting: Date and Call for Talks
(apologies if you receive multiple copies) Dear all, We would like to announce that the fourth meeting of the Ghent Functional Programming Group will be held on Thursday, October 7th at 19h. The location will again be the Technicum building of Ghent University (Sint-Pietersnieuwstraat 41, 9000 Gent). Anyone is free to give a talk, so if you feel like giving one, just contact jejan...@gmail.com. The final program will be announced in a few weeks. Finally, we would also like to remind you that GhentFPG is organizing BelHac, a Haskell hackathon on 5-7 November 2010. More details can be found at http://www.haskell.org/haskellwiki/Ghent_Functional_Programming_Group/BelHac The fifth GhentFPG meeting will take place at this hackathon, so if you plan on going, and feel like giving a talk at this fifth meeting, just contact me. We would be more than happy to have some international speakers at our meeting! Hope to see you then, The GhentFPG Organizing Committee.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
You most certainly meant Prelude Data.Either :t undefined :: (-) Int String undefined :: (-) Int String :: Int - String though it is confusing. Constructors usually take values, but here the values (-) takes are types. Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Ryan Ingram ryani.s...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 3:23 PM 2010/8/31 michael rice nowg...@yahoo.com Hi Vo, Pardon, I grabbed the wrong lines. *Main :t (-) 3 abc interactive:1:1: parse error on input `-' Try *Main :t undefined :: (-) 3 abc You can't write :t some type You have to write :t some value Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Ryan Ingram ryani.s...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 3:07 PM 2010/8/31 michael rice nowg...@yahoo.com Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' :t Int does not make sense but :t undefined :: Int is ok, just like :t undefined :: (-) Int Int What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
2010/8/31 michael rice nowg...@yahoo.com You most certainly meant Prelude Data.Either :t undefined :: (-) Int String undefined :: (-) Int String :: Int - String though it is confusing. Constructors usually take values, but here the values (-) takes are types. Either and (-) are *type* constructors. Just is a (value) constructor. This makes sense: Just 7 is a value, so Just surely constructs a value. Nothing doesn't take an argument but is called a constructor too. Maybe Int is a type, so Maybe surely constructs a type. Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Ryan Ingram ryani.s...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 3:23 PM 2010/8/31 michael rice nowg...@yahoo.com Hi Vo, Pardon, I grabbed the wrong lines. *Main :t (-) 3 abc interactive:1:1: parse error on input `-' Try *Main :t undefined :: (-) 3 abc You can't write :t some type You have to write :t some value Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Ryan Ingram ryani.s...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 3:07 PM 2010/8/31 michael rice nowg...@yahoo.com Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' :t Int does not make sense but :t undefined :: Int is ok, just like :t undefined :: (-) Int Int What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't
Re: [Haskell-cafe] On to applicative
FmapFunc is just a test module I created with instance Functor ((-) r) where ... -- ryan On Tue, Aug 31, 2010 at 12:03 PM, michael rice nowg...@yahoo.com wrote: Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On *Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com* wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On *Tue, 8/31/10, Vo Minh Thu not...@gmail.comhttp://mc/compose?to=not...@gmail.com * wrote: From: Vo Minh Thu not...@gmail.comhttp://mc/compose?to=not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com Cc: haskell-cafe@haskell.orghttp://mc/compose?to=haskell-c...@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.comhttp://mc/compose?to=not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.comhttp://mc/compose?to=not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com Cc: haskell-cafe@haskell.orghttp://mc/compose?to=haskell-c...@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.comhttp://mc/compose?to=nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mc/compose?to=haskell-c...@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 8/31/10 13:27 , michael rice wrote: So it's a type constructor, not a type? Could you please provide a simple example of its usage? Assuming you don't mean the trivial use in defining functions, see Control.Monad.Instances: instance Functor ((-) r) where fmap = (.) instance Monad ((-) r) where return = const f = k = \ r - k (f r) r (The above is the primitive reader functor/monad, see Control.Monad.Reader for more information.) - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkx9Z4EACgkQIn7hlCsL25WgrwCgvFQlObavv1fNOaKDjB/qbk8t 8+IAoLUrenXFzZFfJoYYvSy00uPctnaE =ljiY -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Projects that could use student contributions?
Hi all, This fall I'll be teaching a half-credit introduction to Haskell to some undergrads. As a final project I am thinking of giving them the option of (instead of developing some program/project of their own) contributing to an existing open-source Haskell project. Of course, this requires the existence of projects they could contribute to. I'm sure they exist, but need your help to figure out what they are. So, do you maintain, or know of, any projects with the following characteristics? * might conceivably be interesting to undergraduate CS majors * simple enough that someone could make some non-trivial contributions in the space of 3 or 4 weeks * could use some help! This is a little non-traditional, so we'll see how it goes! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Projects that could use student contributions?
On Tue, Aug 31, 2010 at 1:52 PM, Brent Yorgey byor...@seas.upenn.edu wrote: Hi all, This fall I'll be teaching a half-credit introduction to Haskell to some undergrads. As a final project I am thinking of giving them the option of (instead of developing some program/project of their own) contributing to an existing open-source Haskell project. Of course, this requires the existence of projects they could contribute to. I'm sure they exist, but need your help to figure out what they are. So, do you maintain, or know of, any projects with the following characteristics? * might conceivably be interesting to undergraduate CS majors * simple enough that someone could make some non-trivial contributions in the space of 3 or 4 weeks As interim maintainer of Takusen, I'll vouch for it and say that it would be open and welcoming to such students. Unfortunately, I'm not sure if it qualifies as simple. It uses a lot of FFI and functional dependencies. Otherwise, I think it would be simple enough. Perhaps with a bit of negotiation we could find suitable tasks. One thing that was proposed for Takusen is to build compatibility layers for other Haskell database libraries, such as HDBC. This may actually be a decent project for a student and would possibly free them from the FFI and FDs bits of takusen. The takusen project page is here: http://projects.haskell.org/takusen/ Another idea someone had for takusen was to make a type safe query builder. Right now Takusen itself only requires that the query can be converted to string. So in principle, we could add data types / combinators for building SQL expressions and then have a QueryBuilder - String function. Have you spoken to any other instructors that have used open source contributions as part of a course? I know that at Oregon State University, Dr. Budd has been teaching a class about open source (and how to get started) for several years. I'm sure he'd love to give you advice and he's very friendly. Here is a webpage with contact info: http://eecs.oregonstate.edu/research/members/budd/index.html For the students that do want to contribute to open source, you might encourage them to read Karl Fogel's, Producing Open Source Software: http://producingoss.com/en/index.html * could use some help! At one point I was putting together a series of example OpenGL programs in Haskell. It's bitrotted these days and I'm not sure it needs updated to work with newer versions of HOpenGL. Interested students could polish it up and add more examples to it. I was translating examples from other languages, but creative students could invent their own examples. And, as I'm sure Don Stewart will point out, there is the Haskell reddit list of projects, although possibly too ambitious for 3-4 weeks: http://www.reddit.com/r/haskell_proposals/top/?t=year The Date/Time api might be a good one from that list while running haskell code under google's native client is probably a bit too much to ask for :) I hope that helps, Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Projects that could use student contributions?
On Aug 31, 2010, at 1:52 PM, Brent Yorgey wrote: This fall I'll be teaching a half-credit introduction to Haskell to some undergrads. As a final project I am thinking of giving them the option of (instead of developing some program/project of their own) contributing to an existing open-source Haskell project. Of course, this requires the existence of projects they could contribute to. I'm sure they exist, but need your help to figure out what they are. So, do you maintain, or know of, any projects with the following characteristics? Maybe the Haskell-related Google Summer of Code proposals would be useful to you? http://hackage.haskell.org/trac/summer-of-code/___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Thanks, Brandon, but Ryan gave me what I was looking for. Michael --- On Tue, 8/31/10, Brandon S Allbery KF8NH allb...@ece.cmu.edu wrote: From: Brandon S Allbery KF8NH allb...@ece.cmu.edu Subject: Re: [Haskell-cafe] On to applicative To: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 4:35 PM -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 8/31/10 13:27 , michael rice wrote: So it's a type constructor, not a type? Could you please provide a simple example of its usage? Assuming you don't mean the trivial use in defining functions, see Control.Monad.Instances: instance Functor ((-) r) where fmap = (.) instance Monad ((-) r) where return = const f = k = \ r - k (f r) r (The above is the primitive reader functor/monad, see Control.Monad.Reader for more information.) - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkx9Z4EACgkQIn7hlCsL25WgrwCgvFQlObavv1fNOaKDjB/qbk8t 8+IAoLUrenXFzZFfJoYYvSy00uPctnaE =ljiY -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] :Trace has no history
How do I tell? Does this mean that if the exception is occurring in a haskell library I can't get to it? I am trying to run down a Prelude.read: No Parse error and I need to see the value that it is failing to parse on. Thanks. Steve On Tue, Aug 31, 2010 at 11:05 AM, Pepe Iborra pepeibo...@gmail.com wrote: Hi Steve The debugger only traces calls in interpreted code. Perhaps the call to myMethod is being made from object code? Admittedly, the ghci debugger can take some effort to learn to use properly. Make sure that you give a look to the ghc user guide if you haven't done so yet. Best, pepe On Tuesday, August 31, 2010, Steve sseve...@gmail.com wrote: I am trying to debug a problem in GHCI. I invoke my method with trace but when it breaks on exception i can't get this history. Output is below. Thanks. relude Symbols :set -fbreak-on-exception Prelude Symbols :trace myMethod Loading package HUnit-1.2.2.1 ... linking ... done. Loading package syb-0.1.0.2 ... linking ... done. Loading package base-3.0.3.2 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package Decimal-0.1.0 ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package Diff-0.1.2 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package convertible-1.0.9 ... linking ... done. Loading package utf8-string-0.3.4 ... linking ... done. Loading package HDBC-2.2.6 ... linking ... done. Loading package HDBC-mysql-0.6.3 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.1.7 ... linking ... done. Loading package HTTP-4000.0.9 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package digest-0.0.0.8 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package unix-2.4.0.0 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package zlib-0.5.2.0 ... linking ... done. Loading package zip-archive-0.1.1.6 ... linking ... done. Loading package Core-0.0.1 ... linking ... done. Beginning Update Stopped at exception thrown _exception :: e = GHC.Exception.SomeException (GHC.Exception.D:Exception _ (GHC.Show.D:Show ...) ) (GHC.IO.Exception.IOError Nothing GHC.IO.Exception.UserError ) [exception thrown] Prelude Symbols :history Empty history. Perhaps you forgot to use :trace? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- -- José Iborra http://www.dsic.upv.es/~jiborra -- UPV Valencia Telf. (+34) 96 387 00 00 (ext) 83529 -- Camino de Vera s/n. 46022 Valencia (Spain) -- Steve Severance c. 240.472.9645 e. st...@medwizard.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quick Question for QuickCheck2
Do you have ~/.cabal/bin or $HOME/.cabal/bin ? The latter is preferable as some issues arise with the former... On 1 September 2010 03:29, Lyndon Maydwell maydw...@gmail.com wrote: Yep :) Is there a batch of information that might be useful? I can send any relevant files, aliases, versions, etc at once to help if you like. On Wed, Sep 1, 2010 at 12:35 AM, Sebastian Höhn sebastian.ho...@iig.uni-freiburg.de wrote: Do you have ~/.cabal/bin/ in your PATH? - Sebastian Am 31.08.2010 um 15:57 schrieb Lyndon Maydwell: Yep. Definitely the same user. On Tue, Aug 31, 2010 at 7:35 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 31 August 2010 20:38, Lyndon Maydwell maydw...@gmail.com wrote: ghc-pkg check doesn't list any broken dependencies. You sure this is with the same user? ghci is unlikely to complain about broken libraries if ghc-pkg check doesn't... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] questions about Arrows
Hello -- Three related questions, going from most specific to most general : 1 ) Consider the stream processing arrow which computes a running sum, with two implementations : first using generic ArrowCircuits (rSum); second using Automaton (rSum2) : module Foo where import Control.Arrow import Control.Arrow.Operations import Control.Arrow.Transformer import Control.Arrow.Transformer.All rSum :: ArrowCircuit a = a Int Int rSum = proc x - do rec out - delay 0 - out + x returnA - out rSum2 = Automaton (f 0) where f s n = let s' = s + n in (s', Automaton (f s')) runAuto _ [] = [] runAuto (Automaton f) (x:xs) = let (y, a) = f x in y : runAuto a xs take 10 $ runAuto rSum [1..] [0,1,3,6,10,15,21,28,36,45] take 10 $ runAuto rSum2 [1..] [1,3,6,10,15,21,28,36,45,55] Note that the circuit version starts with the initial value zero. Is there a way to write rSum2 in the general ArrowCircuit form, or using ArrowLoop? 2) Are the ArrowLoop instances for (-), Kleisli Identity, and Kleisli ((-) r) all morally equivalent? (e.g., up to tagging and untagging?) 3) One can define fix in terms of trace and trace in terms of fix. trace f x = fst $ fix (\(m, z) - f (x, z)) fix f = trace (\(x, y) - (f y, f y)) undefined Does this mean we can translate arbitrary recursive functions into ArrowLoop equivalents? Best regards, Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: text 0.8.0.0, fast Unicode text support
New in this release: - Substantial performance improvements. - Bug fixes, and better quality assurance via automated QuickCheck and HPC tests and coverage. - An even nicer API than before. The text library provides an efficient packed, immutable Unicode text type (both strict and lazy), with a powerful loop fusion optimization framework. The 'Text' type represents Unicode character strings, in a time and space-efficient manner. This package provides text processing capabilities that are optimized for performance critical use, both in terms of large data quantities and high speed. The text package provides character-encoding, type-safe case conversion via whole-string case conversion functions. It also provides a range of functions for converting Text values to and from ByteStrings, using several standard encodings (see the text-icu package for a much larger variety of encoding functions). Efficient locale-sensitive support for text I/O is also supported. http://www.serpentine.com/blog/2010/09/01/major-version-of-the-haskell-text-library-0-8-0-0/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Missing documentation in Haskell Platform on Windows
Hello, I installed (succesfully) HAskell Platform 2010.2 on windows and have a small but annoying issue: Some links in HTML documentation lead to broken links. I did not investigate all the links, but I have seen that all doc under Control.Monad.XXX is missing. What am I doing wrong ? Arnaud ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Missing documentation in Haskell Platform on Windows
On 1 September 2010 14:25, Arnaud Bailly arnaud.oq...@gmail.com wrote: Hello, I installed (succesfully) HAskell Platform 2010.2 on windows and have a small but annoying issue: Some links in HTML documentation lead to broken links. I did not investigate all the links, but I have seen that all doc under Control.Monad.XXX is missing. What am I doing wrong ? Is this in the documentation for GHC? Sometimes Haddock links to libraries used when building GHC but aren't shipped with GHC; I'm not sure how to deal with this. (Note: this isn't a Windows-specific problem; it also occurs on Gentoo Linux for example.) Arnaud ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quick Question for QuickCheck2
$HOME/.cabal/bin On Wed, Sep 1, 2010 at 10:55 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Do you have ~/.cabal/bin or $HOME/.cabal/bin ? The latter is preferable as some issues arise with the former... On 1 September 2010 03:29, Lyndon Maydwell maydw...@gmail.com wrote: Yep :) Is there a batch of information that might be useful? I can send any relevant files, aliases, versions, etc at once to help if you like. On Wed, Sep 1, 2010 at 12:35 AM, Sebastian Höhn sebastian.ho...@iig.uni-freiburg.de wrote: Do you have ~/.cabal/bin/ in your PATH? - Sebastian Am 31.08.2010 um 15:57 schrieb Lyndon Maydwell: Yep. Definitely the same user. On Tue, Aug 31, 2010 at 7:35 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 31 August 2010 20:38, Lyndon Maydwell maydw...@gmail.com wrote: ghc-pkg check doesn't list any broken dependencies. You sure this is with the same user? ghci is unlikely to complain about broken libraries if ghc-pkg check doesn't... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: text 0.8.0.0, fast Unicode text support
Is there a summary of the API changes available? I see a new module, but Precis is choking on Data.Text and Data.Text.Lazy, so I'm not sure what existing signatures have been modified. Don't forget, you can always improve the text library yourself. I love to receive patches, requests for improvement, and bug reports. Are there any areas in particular you'd like help with, for either library? I'm happy to assist any effort which will help reduce use of String. [aside] does anybody know how to get a list of what packages somebody's uploaded to Hackage? I think I've updated all mine for the new text version dependency, but I'm worried I forgot some. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
