Re: [Haskell-cafe] Open Source project suitable for 2-3 persons this fall?
There's one of my hobby projects that could use some manpower to bootstrap it into a production-quality tool. It's an HTML templating system; right now it reads input templates in one of two languages (one very declarative, very similar to Python's jinja2, the other being a locally-pure functional language with a curly-bracket syntax), and it can output PHP and JavaScript as well as execute templates directly in Haskell code. There's also a rather experimental JSON-based intermediate format, designed for high-security scenarios (JSON can be parsed quickly, but because it cannot contain arbitrary code, a compromised compiler can be mitigated by whitelisting what the runtime can do; this way, only the runtime has to be audited, not the compiler). There is an incomplete implementation of a PHP library that can interpret this intermediate JSON format, but it hasn't been used in any production-quality project yet. The core part is the compiler, consisting of a Parsec-based parser, an AST, an optimizer, and a few backends. The unique selling points: * Pre-compile your templates - now you can have the cake (expressive clean template language) and eat it too (great performance, because it's pre-compiled to your web app's native language). * Use the same template for PHP, Haskell and JavaScript (and maybe others, too). * Bye bye XSS: HTML-encoding is the default. * Extensible: Hook up your own native functions - it's as simple as adding a function to your template input data, then calling it inside the template. It could use some work in a lot of areas; projects could include, for example: - Getting the JavaScript backend to support 100% of the language features (right now, only the direct-execution and PHP backends pass all tests) - Implement some glue to allow easy embedding in Haskell web applications (yesod / happstack / snap) - Add more features to the input language (some of which would also require some changes to the backends), e.g.: - range literals - list comprehensions - indexed for-each, or some way of getting the current iteration's index; very useful for things like zebra-stripe data grids and such - Add other backends (Python and Ruby would be the most obvious candidates, but I'm really open to anything) - Add more library functions - A better optimizer - Some tooling and integration support, e.g. some kind of mechanism to switch between executing on-the-fly (for development) and using pre-compiled templates (for production), something to implement graceful degrading on the client side (use client-side templates when possible, fall back to postbacks and server-side templates as needed), syntax highlighters for popular editors, etc. Anyway, here's the source: https://bitbucket.org/tdammers/hpaco The PHP lib/script that can produce and run a subset of the JSON intermediate format is here: https://bitbucket.org/tdammers/phpaco (Any contributions, feedback, etc., very welcome) On Thu, Jul 04, 2013 at 05:26:59PM +0200, Anders Bech Mellson wrote: Is there any project that needs working this fall which could be used as a university project? I am in the university (M.Sc. in software development), so I am mainly looking for project ideas (preferably concrete ones). We are 2-3 students that have ~10 hours pr week for 3 months to work on a project. Is there a listing somewhere with project ideas for contributing to the Haskell community? Thanks in advance, Anders ___ 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] Open Source project suitable for 2-3 persons this fall?
Hi Anders, the Darcs project has a few proposals that you can look at: http://darcs.net/GSoC The proposals were written for summer of code projects that involve more time dedication, but they can be reshaped into smaller projects. Feel free to mail me or to discuss it on the #darcs IRC channel on irc.freenode.net. Guillaume ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] newbie question about Functional dependencies conflict between instance declarations:.....
Hello,
I largely don't know what I'm doing or even trying to do, it is a voyage into
the unknownbutif I go...
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
class Foo x y | x - y, y - x
instance Foo Integer Integer
That seems to workand my head seems to say...your created some sort of
binary relation between 2 types...and made Integer,Integer a member of it...
Something like that anyway
Then I go
data Bar
instance Foo Bar x
Error!but I'm think I understand thisI can't claim that Bar,x is a
member of Foo and Integer,Integer is member of Foo and preserve my functional
dependencies, because Bar,Integer is now a member of Foo..
Bad programmer...
So how I naively go
class NotAnInteger a
instance (NotAnInteger x) = Foo Bar x
I haven't declared integer to be NotAnIntegerso (in a closed
world)this would seem to exclude the contradictionbut...
Functional dependencies conflict between instance declarations:
instance Foo Integer Integer -- Defined at liam1.lhs:7:12
instance NotAnInteger x = Foo Bar x -- Defined at liam1.lhs:13:12
So
i)I clearly don't understand something about the type
system.
ii) I don't know how to restrict type variables in instance
declarationsi.e. how do I use the notion of Foo across different
combinations of types, without them colliding.
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Re: [Haskell-cafe] newbie question about Functional dependencies conflict between instance declarations:.....
The constraint on an instance never influences which instance is
selected. So as far as instance selection goes, 'instance Foo x' and
'instance C x = Foo x' are the same. The constraint is only checked
after the instance is selected.
Erik
On Fri, Jul 5, 2013 at 2:43 PM, Nicholls, Mark nicholls.m...@vimn.com wrote:
Hello,
I largely don’t know what I’m doing or even trying to do, it is a voyage
into the unknown….but….if I go…
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
class Foo x y | x - y, y - x
instance Foo Integer Integer
That seems to work….and my head seems to say…your created some sort of
binary relation between 2 types…and made Integer,Integer a member of it…
Something like that anyway….
Then I go….
data Bar
instance Foo Bar x
Error!but I’m think I understand this….I can’t claim that Bar,x is a
member of Foo and Integer,Integer is member of Foo and preserve my
functional dependencies, because Bar,Integer is now a member of Foo..
Bad programmer…….
So how I naively go….
class NotAnInteger a
instance (NotAnInteger x) = Foo Bar x
I haven’t declared integer to be “NotAnInteger”….so (in a closed
world)….this would seem to exclude the contradiction….but…
Functional dependencies conflict between instance declarations:
instance Foo Integer Integer -- Defined at liam1.lhs:7:12
instance NotAnInteger x = Foo Bar x -- Defined at liam1.lhs:13:12
So
i)I clearly don’t understand something about the type
system.
ii) I don’t know how to restrict type variables in
instance declarations….i.e. how do I use the notion of “Foo” across
different combinations of types, without them colliding.
CONFIDENTIALITY NOTICE
This e-mail (and any attached files) is confidential and protected by
copyright (and other intellectual property rights). If you are not the
intended recipient please e-mail the sender and then delete the email and
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Communicating by email is not 100% secure and carries risks such as delay,
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amendment. If you communicate with us by e-mail, you acknowledge and assume
these risks, and you agree to take appropriate measures to minimise these
risks when e-mailing us.
MTV Networks International, MTV Networks UK Ireland, Greenhouse,
Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions
International, Be Viacom, Viacom International Media Networks and VIMN and
Comedy Central are all trading names of MTV Networks Europe. MTV Networks
Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks
Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent,
London, NW1 8TT.
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Re: [Haskell-cafe] newbie question about Functional dependencies conflict between instance declarations:.....
You're running into the open worldassumption--anybody could come along
and make Integer part of your NotAnInteger class, and there's nothing you
can do to stop them. This is a design tradeoff for typeclasses: typeclass
instances are always global and are exported to all other modules you use.
This means you cannot ensure a type is *not* part of a typeclass. (Or, at
the very least, you can't convince GHC of this fact.)
For more information about this, take a look at the following StackOverflow
question:
http://stackoverflow.com/questions/8728596/explicitly-import-instances
On Jul 5, 2013 8:47 AM, Nicholls, Mark nicholls.m...@vimn.com wrote:
Hello,
** **
I largely don’t know what I’m doing or even trying to do, it is a voyage
into the unknown….but….if I go…
** **
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
** **
class Foo x y | x - y, y - x
instance Foo Integer Integer
** **
That seems to work….and my head seems to say…your created some sort of
binary relation between 2 types…and made Integer,Integer a member of it…
** **
Something like that anyway….
** **
Then I go….
** **
data Bar
** **
instance Foo Bar x
** **
Error!but I’m think I understand this….I can’t claim that Bar,x is a
member of Foo and Integer,Integer is member of Foo and preserve my
functional dependencies, because Bar,Integer is now a member of Foo..***
*
** **
Bad programmer…….
** **
** **
So how I naively go….
** **
** **
class NotAnInteger a
** **
instance (NotAnInteger x) = Foo Bar x
** **
I haven’t declared integer to be “NotAnInteger”….so (in a closed
world)….this would seem to exclude the contradiction….but…
** **
** **
Functional dependencies conflict between instance declarations:
instance Foo Integer Integer -- Defined at liam1.lhs:7:12
instance NotAnInteger x = Foo Bar x -- Defined at liam1.lhs:13:12**
**
** **
So
**i)**I clearly don’t understand something about the
type system.
**ii) **I don’t know how to restrict type variables in
instance declarations….i.e. how do I use the notion of “Foo” across
different combinations of types, without them colliding.
** **
** **
** **
** **
** **
** **
** **
CONFIDENTIALITY NOTICE
This e-mail (and any attached files) is confidential and protected by
copyright (and other intellectual property rights). If you are not the
intended recipient please e-mail the sender and then delete the email and
any attached files immediately. Any further use or dissemination is
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While MTV Networks Europe has taken steps to ensure that this email and
any attachments are virus free, it is your responsibility to ensure that
this message and any attachments are virus free and do not affect your
systems / data.
Communicating by email is not 100% secure and carries risks such as delay,
data corruption, non-delivery, wrongful interception and unauthorised
amendment. If you communicate with us by e-mail, you acknowledge and assume
these risks, and you agree to take appropriate measures to minimise these
risks when e-mailing us.
MTV Networks International, MTV Networks UK Ireland, Greenhouse,
Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions
International, Be Viacom, Viacom International Media Networks and VIMN and
Comedy Central are all trading names of MTV Networks Europe. MTV Networks
Europe is a partnership between MTV Networks Europe Inc. and Viacom
Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley
Crescent, London, NW1 8TT.
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Re: [Haskell-cafe] newbie question about Functional dependencies conflict between instance declarations:.....
Ah
So it isn't a closed world
So how do I stop my instances clashing?
The x in
instance Foo Bar x
is never intended to be Integer.
Mark Nicholls | Lead broadcast corporate architect, Programmes Development
- Viacom International Media Networks
A: 17-29 Hawley Crescent London NW1 8TT | e:
nicholls.m...@vimn.commailto:m...@vimn.com T: +44 (0)203 580 2223
[Description: cid:image001.png@01CD488D.9204D030]
From: Tikhon Jelvis [mailto:tik...@jelv.is]
Sent: 05 July 2013 2:08 PM
To: Nicholls, Mark
Cc: haskell-cafe
Subject: Re: [Haskell-cafe] newbie question about Functional dependencies
conflict between instance declarations:.
You're running into the open worldassumption--anybody could come along and
make Integer part of your NotAnInteger class, and there's nothing you can do to
stop them. This is a design tradeoff for typeclasses: typeclass instances are
always global and are exported to all other modules you use. This means you
cannot ensure a type is *not* part of a typeclass. (Or, at the very least, you
can't convince GHC of this fact.)
For more information about this, take a look at the following StackOverflow
question: http://stackoverflow.com/questions/8728596/explicitly-import-instances
On Jul 5, 2013 8:47 AM, Nicholls, Mark
nicholls.m...@vimn.commailto:nicholls.m...@vimn.com wrote:
Hello,
I largely don't know what I'm doing or even trying to do, it is a voyage into
the unknownbutif I go...
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
class Foo x y | x - y, y - x
instance Foo Integer Integer
That seems to workand my head seems to say...your created some sort of
binary relation between 2 types...and made Integer,Integer a member of it...
Something like that anyway
Then I go
data Bar
instance Foo Bar x
Error!but I'm think I understand thisI can't claim that Bar,x is a
member of Foo and Integer,Integer is member of Foo and preserve my functional
dependencies, because Bar,Integer is now a member of Foo..
Bad programmer...
So how I naively go
class NotAnInteger a
instance (NotAnInteger x) = Foo Bar x
I haven't declared integer to be NotAnIntegerso (in a closed
world)this would seem to exclude the contradictionbut...
Functional dependencies conflict between instance declarations:
instance Foo Integer Integer -- Defined at liam1.lhs:7:12
instance NotAnInteger x = Foo Bar x -- Defined at liam1.lhs:13:12
So
i)I clearly don't understand something about the type
system.
ii) I don't know how to restrict type variables in instance
declarationsi.e. how do I use the notion of Foo across different
combinations of types, without them colliding.
CONFIDENTIALITY NOTICE
This e-mail (and any attached files) is confidential and protected by copyright
(and other intellectual property rights). If you are not the intended recipient
please e-mail the sender and then delete the email and any attached files
immediately. Any further use or dissemination is prohibited.
While MTV Networks Europe has taken steps to ensure that this email and any
attachments are virus free, it is your responsibility to ensure that this
message and any attachments are virus free and do not affect your systems /
data.
Communicating by email is not 100% secure and carries risks such as delay, data
corruption, non-delivery, wrongful interception and unauthorised amendment. If
you communicate with us by e-mail, you acknowledge and assume these risks, and
you agree to take appropriate measures to minimise these risks when e-mailing
us.
MTV Networks International, MTV Networks UK Ireland, Greenhouse, Nickelodeon
Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be
Viacom, Viacom International Media Networks and VIMN and Comedy Central are all
trading names of MTV Networks Europe. MTV Networks Europe is a partnership
between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for
service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.
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Communicating by email is not 100%
[Haskell-cafe] Extending Type Classes
Hello all, I was looking for my master thesis topic and my supervisor suggested an idea of extending class system so it enables refactoring Type Class hierarchy without affecting client source code which is using refactored classes. One example is Functor - Applicative - Monad problem and corresponding proposal [1]. But this proposal instead of allowing the change through extending Type Classes forces client code to prepare for the new class layout and then switch the classes to the new layout. My goal is rather to allow direct changes in class hierarchy without affecting client source code. I have found different proposals approaching this problem on HaskellWiki, some of them are overlapping, some of them refer each other. The most promising to me seems Default superclass instances proposal [2]. This one is somehow implemented in the Strathclyde Haskell Enhancement (SHE) [3] but I haven't found much reference or user experience really. So the reason why I write this email is to ask you for some tips where above mentioned problem occurs in real source code. I would like to investigate some real examples before designing some ad hoc changes to the Type Classes system. Besides that I'd appreciate anyone who has used default superclass instances in SHE to share his experience. And last but not least I am always grateful for any comments and suggestions. Best wishes Frantisek [1] http://www.haskell.org/haskellwiki/Functor_hierarchy_proposal [2] http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances [3] https://personal.cis.strath.ac.uk/conor.mcbride/pub/she/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Basic Parsec float integer parsing question
Dear list,
Sorry for asking a simple parsec question, but both Parsec and Haskell is
new to me, so please be gentle :-)
I have this code:
import Text.ParserCombinators.Parsec
import Text.Parsec.Token
import Text.ParserCombinators.Parsec.Char
data VariableLine = VariableLine String String deriving Show
data TierType = IntervalTier | PointTier deriving Show
data Tier = Tier TierType String Float Float Integer
data Label = Interval Float Float String
data LabelFile = LabelFile Float Float
symbol :: Parser Char
symbol = oneOf !#$%|*+-/:=?@^_~
testString = intervals [1]:\nxmin = 0 \nxmax =
0.028192 \ntext = \\
headTS1 = File type = \ooTextFile\\nObject class = \TextGrid\\n\nxmin
=
header :: Parser LabelFile
header = do
headTS1
start - float
string \nxmax =
end - float
string \ntiers? exists\nsize =
integer
char '\n'
return $ LabelFile start end
Loading it into ghci I get :
Prelude :l parsectest.hs
[1 of 1] Compiling Main ( parsectest.hs, interpreted )
parsectest.hs:21:9:
Couldn't match type `[]'
with `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity'
Expected type: Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity Char
Actual type: [Char]
In a stmt of a 'do' block: headTS1
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:22:18:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String ()
Data.Functor.Identity.Identity Float'
with actual type `GenTokenParser s0 u0 m0
- Text.Parsec.Prim.ParsecT s0 u0 m0
Double'
In a stmt of a 'do' block: start - float
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:24:16:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String ()
Data.Functor.Identity.Identity Float'
with actual type `GenTokenParser s1 u1 m1
- Text.Parsec.Prim.ParsecT s1 u1 m1
Double'
In a stmt of a 'do' block: end - float
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:26:9:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String ()
Data.Functor.Identity.Identity a0'
with actual type `GenTokenParser s2 u2 m2
- Text.Parsec.Prim.ParsecT s2 u2 m2
Integer'
In a stmt of a 'do' block: integer
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
Failed, modules loaded: none.
I'm sure I'm doing something really stupid here, but I need help to get
through this problem. I've used the predefined letter parser at other
places in the code, so I can't understand why float and integer does
not work.
/Fredrik
--
Life is like a trumpet - if you don't put anything into it, you don't get
anything out of it.
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Re: [Haskell-cafe] Basic Parsec float integer parsing question
Token parsers are specific to different languages. Afterall, haskell
parses floats differently than C, which is different from java
(probably). In order to use it in your code you have to tell it that,
like so:
haskelldef = makeTokenParser haskellDef
header :: Parser LabelFile
header = do
string headTS1
start - fmap double2Float $ float haskelldef
string \nxmax =
end - fmap double2Float $ float haskelldef
string \ntiers? exists\nsize =
integer haskelldef
char '\n'
return $ LabelFile start end
You'll need to import GHC.Float (double2Float) to get those parsed
values as floats.
On Fri, Jul 5, 2013 at 12:42 PM, Fredrik Karlsson dargo...@gmail.com wrote:
Dear list,
Sorry for asking a simple parsec question, but both Parsec and Haskell is
new to me, so please be gentle :-)
I have this code:
import Text.ParserCombinators.Parsec
import Text.Parsec.Token
import Text.ParserCombinators.Parsec.Char
data VariableLine = VariableLine String String deriving Show
data TierType = IntervalTier | PointTier deriving Show
data Tier = Tier TierType String Float Float Integer
data Label = Interval Float Float String
data LabelFile = LabelFile Float Float
symbol :: Parser Char
symbol = oneOf !#$%|*+-/:=?@^_~
testString = intervals [1]:\nxmin = 0 \nxmax = 0.028192
\ntext = \\
headTS1 = File type = \ooTextFile\\nObject class = \TextGrid\\n\nxmin
=
header :: Parser LabelFile
header = do
headTS1
start - float
string \nxmax =
end - float
string \ntiers? exists\nsize =
integer
char '\n'
return $ LabelFile start end
Loading it into ghci I get :
Prelude :l parsectest.hs
[1 of 1] Compiling Main ( parsectest.hs, interpreted )
parsectest.hs:21:9:
Couldn't match type `[]'
with `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity'
Expected type: Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity Char
Actual type: [Char]
In a stmt of a 'do' block: headTS1
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:22:18:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity
Float'
with actual type `GenTokenParser s0 u0 m0
- Text.Parsec.Prim.ParsecT s0 u0 m0
Double'
In a stmt of a 'do' block: start - float
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:24:16:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity
Float'
with actual type `GenTokenParser s1 u1 m1
- Text.Parsec.Prim.ParsecT s1 u1 m1
Double'
In a stmt of a 'do' block: end - float
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:26:9:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity
a0'
with actual type `GenTokenParser s2 u2 m2
- Text.Parsec.Prim.ParsecT s2 u2 m2
Integer'
In a stmt of a 'do' block: integer
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
Failed, modules loaded: none.
I'm sure I'm doing something really stupid here, but I need help to get
through this problem.
[Haskell-cafe] Fwd: Basic Parsec float integer parsing question
Forwarding to the list.
-- Forwarded message --
From: Fredrik Karlsson dargo...@gmail.com
Date: Fri, Jul 5, 2013 at 11:42 AM
Subject: [Haskell-cafe] Basic Parsec float integer parsing question
To: haskell-cafe@haskell.org
Dear list,
Sorry for asking a simple parsec question, but both Parsec and Haskell
is new to me, so please be gentle :-)
I have this code:
import Text.ParserCombinators.Parsec
import Text.Parsec.Token
import Text.ParserCombinators.Parsec.Char
data VariableLine = VariableLine String String deriving Show
data TierType = IntervalTier | PointTier deriving Show
data Tier = Tier TierType String Float Float Integer
data Label = Interval Float Float String
data LabelFile = LabelFile Float Float
symbol :: Parser Char
symbol = oneOf !#$%|*+-/:=?@^_~
testString = intervals [1]:\nxmin = 0 \nxmax =
0.028192 \ntext = \\
headTS1 = File type = \ooTextFile\\nObject class = \TextGrid\\n\nxmin =
header :: Parser LabelFile
header = do
headTS1
start - float
string \nxmax =
end - float
string \ntiers? exists\nsize =
integer
char '\n'
return $ LabelFile start end
Loading it into ghci I get :
Prelude :l parsectest.hs
[1 of 1] Compiling Main ( parsectest.hs, interpreted )
parsectest.hs:21:9:
Couldn't match type `[]'
with `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity'
Expected type: Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity Char
Actual type: [Char]
In a stmt of a 'do' block: headTS1
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:22:18:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String ()
Data.Functor.Identity.Identity Float'
with actual type `GenTokenParser s0 u0 m0
- Text.Parsec.Prim.ParsecT s0 u0 m0 Double'
In a stmt of a 'do' block: start - float
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:24:16:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String ()
Data.Functor.Identity.Identity Float'
with actual type `GenTokenParser s1 u1 m1
- Text.Parsec.Prim.ParsecT s1 u1 m1 Double'
In a stmt of a 'do' block: end - float
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
parsectest.hs:26:9:
Couldn't match expected type `Text.Parsec.Prim.ParsecT
String () Data.Functor.Identity.Identity a0'
with actual type `GenTokenParser s2 u2 m2
- Text.Parsec.Prim.ParsecT s2 u2 m2 Integer'
In a stmt of a 'do' block: integer
In the expression:
do { headTS1;
start - float;
string
\
\xmax = ;
end - float;
}
In an equation for `header':
header
= do { headTS1;
start - float;
string
\
\xmax = ;
}
Failed, modules loaded: none.
I'm sure I'm doing something really stupid here, but I need help to
get through this problem. I've used the predefined letter parser at
other places in the code, so I can't understand why float and
integer does not work.
/Fredrik
--
Life is like a trumpet - if you don't put anything into it, you don't
get anything out of it.
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[Haskell-cafe] same function's type accepted in top level, but rejected in where clause
Hi all,
I came across an interesting type checker error, a function is
accepted in top level, but rejected by type checker when moved to
`where ...` clause.
I moved required code to a new module for demonstration purposes:
module Bug where
fix :: (a - a) - a
fix f = let x = f x in x
data Fix f = Fix (f (Fix f))
unFix :: Fix f - f (Fix f)
unFix (Fix a) = a
data ListF a l = NilF | ConsF a l
instance Functor (ListF a) where
fmap _ NilF= NilF
fmap f (ConsF a l) = ConsF a (f l)
fold :: Functor f = (f a - a) - Fix f - a
fold f a = f (fmap (fold f) (unFix a {- f (Fix f) -}))
unfold :: Functor f = (a - f a) - a - Fix f
unfold f a = Fix (fmap (unfold f) (f a))
Now, after this code, type checker accept this function:
iterateListF :: (a - a) - a - Fix (ListF a)
iterateListF fn e = unfold (foldFn fn) e
foldFn :: (a - a) - a - ListF a a
foldFn fn a = ConsF a (fn a)
But rejects this:
iterateListF :: (a - a) - a - Fix (ListF a)
iterateListF fn e = unfold f e
where
f :: a - ListF a a
f a = ConsF a (fn a)
With error:
bug.hs:27:20:
Couldn't match expected type `a1' with actual type `a'
`a1' is a rigid type variable bound by
the type signature for f :: a1 - ListF a1 a1 at bug.hs:26:10
`a' is a rigid type variable bound by
the type signature for
iterateListF :: (a - a) - a - Fix (ListF a)
at bug.hs:23:17
In the return type of a call of `fn'
In the second argument of `ConsF', namely `(fn a)'
In the expression: ConsF a (fn a)
Changing type variables in type of `f` to `x` fails with this error:
bug.hs:28:20:
Couldn't match expected type `x' with actual type `a'
`x' is a rigid type variable bound by
the type signature for f :: x - ListF x x at bug.hs:27:10
`a' is a rigid type variable bound by
the type signature for
iterateListF :: (a - a) - a - Fix (ListF a)
at bug.hs:24:17
In the return type of a call of `fn'
In the second argument of `ConsF', namely `(fn a)'
In the expression: ConsF a (fn a)
Failed, modules loaded: none.
.. and this is strange because error message describes function as it
is before changing `a` to `x`.
Any ideas why this definition rejected? Is this a bug in GHC?
---
Ömer Sinan Ağacan
http://osa1.net
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Re: [Haskell-cafe] same function's type accepted in top level, but rejected in where clause
If you remove the type signature from f in the where clause it will
work. The reason is because the type signature listed there, the a is
a different a than in the top level signature. If you change it from
a to x, it says it should be the a that you can't seem to specify.
If you add the pragma ScopedTypeVariables to your file, it works the
way you would assume. However you will have to change the toplevel
signature to iterateListF :: forall a. (a - a) - a - Fix (ListF a)
in order to make it work (added the forall a.).
On Fri, Jul 5, 2013 at 4:35 PM, Ömer Sinan Ağacan omeraga...@gmail.com wrote:
Hi all,
I came across an interesting type checker error, a function is
accepted in top level, but rejected by type checker when moved to
`where ...` clause.
I moved required code to a new module for demonstration purposes:
module Bug where
fix :: (a - a) - a
fix f = let x = f x in x
data Fix f = Fix (f (Fix f))
unFix :: Fix f - f (Fix f)
unFix (Fix a) = a
data ListF a l = NilF | ConsF a l
instance Functor (ListF a) where
fmap _ NilF= NilF
fmap f (ConsF a l) = ConsF a (f l)
fold :: Functor f = (f a - a) - Fix f - a
fold f a = f (fmap (fold f) (unFix a {- f (Fix f) -}))
unfold :: Functor f = (a - f a) - a - Fix f
unfold f a = Fix (fmap (unfold f) (f a))
Now, after this code, type checker accept this function:
iterateListF :: (a - a) - a - Fix (ListF a)
iterateListF fn e = unfold (foldFn fn) e
foldFn :: (a - a) - a - ListF a a
foldFn fn a = ConsF a (fn a)
But rejects this:
iterateListF :: (a - a) - a - Fix (ListF a)
iterateListF fn e = unfold f e
where
f :: a - ListF a a
f a = ConsF a (fn a)
With error:
bug.hs:27:20:
Couldn't match expected type `a1' with actual type `a'
`a1' is a rigid type variable bound by
the type signature for f :: a1 - ListF a1 a1 at bug.hs:26:10
`a' is a rigid type variable bound by
the type signature for
iterateListF :: (a - a) - a - Fix (ListF a)
at bug.hs:23:17
In the return type of a call of `fn'
In the second argument of `ConsF', namely `(fn a)'
In the expression: ConsF a (fn a)
Changing type variables in type of `f` to `x` fails with this error:
bug.hs:28:20:
Couldn't match expected type `x' with actual type `a'
`x' is a rigid type variable bound by
the type signature for f :: x - ListF x x at bug.hs:27:10
`a' is a rigid type variable bound by
the type signature for
iterateListF :: (a - a) - a - Fix (ListF a)
at bug.hs:24:17
In the return type of a call of `fn'
In the second argument of `ConsF', namely `(fn a)'
In the expression: ConsF a (fn a)
Failed, modules loaded: none.
.. and this is strange because error message describes function as it
is before changing `a` to `x`.
Any ideas why this definition rejected? Is this a bug in GHC?
---
Ömer Sinan Ağacan
http://osa1.net
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Re: [Haskell-cafe] same function's type accepted in top level, but rejected in where clause
If you add the pragma ScopedTypeVariables to your file, it works the way you would assume. However you will have to change the toplevel signature to iterateListF :: forall a. (a - a) - a - Fix (ListF a) in order to make it work (added the forall a.). Thanks, that worked. As far as I understand, the problem is because in this definition: where f :: a - ListF a a f a = ConsF a (fn a) There's an implicit quantifier in type of `f`, like this: `f :: forall a. a - ListF a a`. When I add `ScopedTypeVariables` and `forall a. ...` in top level definition, it's like all `a`s in scope of top level definition are same, except when explicitly defined as `forall a. ...`. Is my intuition correct? --- Ömer Sinan Ağacan http://osa1.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Postdocs and Research Programmer for Compositional Learning via Generalized Automatic Differentiation
We are adding exact first-class derivative calculation operators (Automatic Differentiation or AD) to the lambda calculus, and embodying the combination in a production-quality fast system suitable for numeric computing in general, and compositional machine learning methods in particular. To the programming language community, we seek to contribute a way to make numeric software faster, more robust, and easier to write. To the machine learning community, in addition to the above practical benefits, we seek to contribute a system that embodies *compositionality*, in that gradient optimisation can be automatically and efficiently performed on systems themselves consisting of many components, even when such components may internally perform optimisation. (Examples of this include, say, optimisation of the rules of a multi-player game to cause the players actions to satisfy some desiderata, where the players themselves optimise their own strategy with using a simple model of the opponent which they optimise according to their opponent's behaviour; or multi-agent learning where one agent learns an internal model of another agent, where that internal model itself performs learning.) To this end, we are seeking two postdoctoral researchers and one research programmer with interest and experience in a cohert subset of: programming language theory, numerics, automatic differentiation, and machine learning. Inquiries to: Barak A. Pearlmutter ba...@cs.nuim.ie Informal announcment with more details: http://www.bcl.hamilton.ie/~barak/ad-fp-positions.html, which will have a reference to the formal announcement when it becomes available. -- Barak A. Pearlmutter Hamilton Institute Dept Computer Science NUI Maynooth ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: Ajhc Haskell Compiler 0.8.0.7 Release
We are happy to announce Ajhc 0.8.0.7. You can program interrupt handler with Haskell language on this release. But not yet collect (big) patch sets, the changes will be merged to jhc. You can get Ajhc using cabal install ajhc command. The usage is found at Ajhc's project web site http://ajhc.metasepi.org/. The source code at https://github.com/ajhc/ajhc/tags. Welcome sending any bugs or your ideas to https://github.com/ajhc/ajhc/issues. ## An example of interrupt handler written with Haskell https://github.com/ajhc/demo-cortex-m3/tree/master/stm32f3-discovery The demo for Cortex-M4 has main context and intrrupt context. The main context waits time expire with polling counter. https://github.com/ajhc/demo-cortex-m3/blob/master/stm32f3-discovery/hs_src/Intr.hs#L17 The interrupt context is called from clock exception, and decrement counter. https://github.com/ajhc/demo-cortex-m3/blob/master/stm32f3-discovery/hs_src/Intr.hs#L9 ## Other changes * Guard StablePtr critical section. * Add _JHC_JGC_SAVING_MALLOC_HEAP option for getting smaller malloc heap. * Link forkIO to forkOS. Enjoy! :) - - - Metasepi team ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Ajhc Haskell Compiler 0.8.0.7 Release
Is this a practical way to write Android and iPhone code? I don't mean console programs, I mean realistic smartphone apps. Seeing as smartphones outsell laptops by about 10 to 1 nowadays, it would be nice if it was. Adrian. On 6 Jul 2013 12:03, Kiwamu Okabe kiw...@debian.or.jp wrote: We are happy to announce Ajhc 0.8.0.7. You can program interrupt handler with Haskell language on this release. But not yet collect (big) patch sets, the changes will be merged to jhc. You can get Ajhc using cabal install ajhc command. The usage is found at Ajhc's project web site http://ajhc.metasepi.org/. The source code at https://github.com/ajhc/ajhc/tags. Welcome sending any bugs or your ideas to https://github.com/ajhc/ajhc/issues. ## An example of interrupt handler written with Haskell https://github.com/ajhc/demo-cortex-m3/tree/master/stm32f3-discovery The demo for Cortex-M4 has main context and intrrupt context. The main context waits time expire with polling counter. https://github.com/ajhc/demo-cortex-m3/blob/master/stm32f3-discovery/hs_src/Intr.hs#L17 The interrupt context is called from clock exception, and decrement counter. https://github.com/ajhc/demo-cortex-m3/blob/master/stm32f3-discovery/hs_src/Intr.hs#L9 ## Other changes * Guard StablePtr critical section. * Add _JHC_JGC_SAVING_MALLOC_HEAP option for getting smaller malloc heap. * Link forkIO to forkOS. Enjoy! :) - - - Metasepi team ___ 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
