The docs at
http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:gcd
give a NB mentioning that (abs minBound == minBound) is possible for
fixed-width types.
This holds, for example, at Int. It is also the case that (negate minBound
== minBound).
Two questions:
1) This
but an
alpha-equivalent type does exhibit it in my larger program.
On Fri, May 27, 2011 at 12:04 PM, Nicolas Frisby
nicolas.fri...@gmail.com wrote:
With the three modules at the end of this email, I get some
interesting results. Note that none of the constructors are exported,
yet Template Haskell can
This message motivates adding support to Template Haskell for code
that can be spliced but can no longer be intensionally analyzed.
I'm trying to use the well-known technique of a hidden constructor in
order to represent values that satisfy a particular predicate.
module Safe (Safe(), safe,
Whith the three modules at the end of this email, I get some
interesting results. Note that none of the constructors are exported,
yet Template Haskell can see (and splice in variable occurrences of!)
T, C2, W1, and W4.
If you load Dump into GHCi, you get to see the Info that TH provides
when you
For this vanilla program
module Main where
main = print $ fib 40
fib 0 = 1
fib 1 = 1
fib n = fib (n - 1) + fib (n - 2)
with these commands
$ ghc -prof -auto-all -rtsopts -O --make Main.hs -o Main
$ ./Main +RTS -p
all of the %time cells in the generated Main.prof file are 0.0, as is
the
Whoops: I'm running Haskell Platform 2011.2.0.1.
OS X 10.6.7
i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664) (if
that matters?) Out of my depth here.
On Fri, May 6, 2011 at 5:07 PM, Nicolas Frisby nicolas.fri...@gmail.com wrote:
For this vanilla program
module Main where
I haven't been able to find it via Google or Haddock. An old message
suggests is was just a matter of exceptions?
I only want to use the IO for generating Data.Uniques to pair with
STRefs in order to make a map of them. I'm guessing this would be a
safe use since it's exception free (... right?).
Alternatively:
let f :: some type involving a
f = ...
f' :: a - some type involving a
f' _ = f
in f' (undefined :: Int) normal f arguments
On Thu, Mar 18, 2010 at 12:10 PM, Max Bolingbroke
batterseapo...@hotmail.com wrote:
Hi Paul,
You should be able to introduce \Lambda at the
Each time I find myself needing to use the wrapping functions
necessary for this embeddings, I grumble. Does anyone have a favorite
use-pattern for ameliorating these quickly ubiquitous conversions?
For runKleisli, I was considering something like
okKleisli ::
(Control.Arrow.Kleisli m a b -
thinking of exporting a MyLibrary.Main or MyLibrary.Instances module.
Anyone have experience with this approach in a library design? Is it
worth the user's extra import? Any pitfalls?
On Sun, Dec 7, 2008 at 4:57 PM, Nicolas Frisby nicolas.fri...@gmail.com wrote:
Seems I got ahead of myself
Any movement on this?
(I am actually just looking forward to generating kind ascriptions and
having access to the kinds when processing TH.Dec, TH.Type, and such.)
2008/11/27 Simon Peyton-Jones simo...@microsoft.com:
I've been away. I hope others will reply to this thread too; whatever you
a) away. So
GHC must try that route. If it fails, you want it to back up to a
notationally more convenient type, but GHC can't do that, I'm afraid
Simon
| -Original Message-
| From: [EMAIL PROTECTED] [mailto:haskell-cafe-
| [EMAIL PROTECTED] On Behalf Of Nicolas Frisby
| Sent: 06
With these three declarations
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
class C a where c :: a
class C a = D a where d :: a
instance C a = D a where d = c
ghci exhibits this behavior:
* :t d
d :: (C a) = a
Where I would prefer d :: (D a) = a. In my
Perhaps this ticket is related?
http://hackage.haskell.org/trac/ghc/ticket/714
On Thu, Dec 4, 2008 at 9:38 PM, Nicolas Frisby [EMAIL PROTECTED] wrote:
From the error below, I'm inferring that the RHS of the associated
type definition can only contain type variables from the instance
head
1) Type families, associated types, synonyms... can anything replace
the use of TypeCast for explicit instance selection? Section 2, bullet
4 of http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap indicates
a negative response. Any other ideas?
2) Any progress/options for kind polymorphism in
From the error below, I'm inferring that the RHS of the associated
type definition can only contain type variables from the instance
head, not the instance context. I didn't explicitly see this
restriction when reading the GHC/Type_families entry.
Could perhaps the a b - bn functional dependency
When using template haskell (via Derive) to generate this (exact) instance:
instance Foldable ((-) Int) = Foldable
Data.Derivable.InterpreterLib.Test.List
where foldMap f (Cons x0 x1) = (const mempty Cons `mappend`
foldMap f x0) `mappend` foldMap f x1
foldMap f (Nil) = const
I think I've exhausted my options without catching exceptions.
If I have an invalid symbolic link, how can I identify that it exists?
(Sorry about the line wrap.)
tmp$ ls -l# no tricks up my sleeve, empty directory
tmp$ touch foo
tmp$ ln -s foo bar
tmp$ ls -l
total 8
lrwxr-xr-x 1
Ah the magic of using a mailing list... I just realized that using
getDirectoryContents lists the entry.
Still, a doesLinkExist function might be nice...
On Wed, Aug 27, 2008 at 11:46 PM, Nicolas Frisby
[EMAIL PROTECTED] wrote:
I think I've exhausted my options without catching exceptions
I have a question about cabal's behavior for the build command. When
using the build command on a cabalized project, any version changes
for installed packages go unnoticed - the necessary modules in the
project are not re-compiled. If however, you run the configure command
(though the .cabal file
I have accomplished this in two ways. Either drop the reflexive rule
and introduce a void sentinel type or use TypeEq (... you said
everything was fair game!) to explicitly specify the preference for
the reflexive case over the inductive case. An advantage of TypeEq is
that you can avoid
It sounds like the semantics of the MonadPlus methods are
under-specified. I recall once writing a newtype wrapper to treat the
same non-determinism monad with different mplus semantics, akin to cut
versus backtracking.
I think of MonadPlus as a less expressive version of msplit, from
This paper, with a pdf available at Patricia Johann's publications page
http://crab.rutgers.edu/~pjohann/
seems to be related.
Initial Algebra Semantics is Enough! Patricia Johann and Neil Ghani.
Proceedings, Typed Lambda Calculus and Applications 2007 (TLCA'07)
Hope that helps.
On Jan
Extensionality says that the only observable properties of functions
are the outputs they give for particular inputs. Accepting
extensionality as a Good Thing implies that enabling the user to
define a function that can differentiate between f x = x + x and g x =
2 * x is a Bad Thing.
Note that
This is a fine warning you both point out, but I would suggest that it
distracts from the OP's question.
The previous, germane discussion holds if we assume that i) both f and
g have type Integer - Integer, ii) the compiler writer is not out to
get us, and iii) the GMP library, if used by that
It seems there is previous background here that I am unaware of. I'll
chime in anyway.
What you describe as the wrong semantics seems to me to be the more
appropriate. I am inferring that your expected behavior is explained
such that the first server match ought to fail (and fall through to
the
I've got a first draft with the newtype and just an instance for list.
If you'd prefer fewer questions, please let me know ;)
0) I've cabalised it (lazy-binary), but I don't have anywhere to host it.
Would it be appropriate to host on darcs.haskell.org or HackageDB (yet?).
Suggestions?
1)
In light of this discussion, I think the fully spine-strict list instance
does more good than bad argument is starting to sound like a premature
optimization. Consequently, using a newtype to treat the necessarily lazy
instances as special cases is an inappropriate bandaid.
My current opinion: If
On Nov 19, 2007 4:16 PM, Duncan Coutts [EMAIL PROTECTED] wrote:
On Mon, 2007-11-19 at 13:39 -0800, Don Stewart wrote:
nicolas.frisby:
*snip*
1) The fact that serialisation is fully strict for 32760 bytes but not
for
32761 makes the direct application of strictCheck
It seems the meaning of the -main-is switch for GHC and the Main-Is
build option for Cabal executables differ. With GHC, I can point to
any function main in any module, but in Cabal I must point to a
filename with precisely the module name Main. This is tying my hands
with regard to organizing a
I've noticed a few posts on the cafe, including my own experience,
where the spine-strictness of the Binary instance for lists caused
some confusion. I'd like to suggest an approach to preventing this
confusion in the future, or at least making it easier to resolve.
Having decided that it is
It is truly irresponsible to post such interesting links on a mailing list! :)
I resent and thank you for the last couple hours.
On 10/17/07, Dan Weston [EMAIL PROTECTED] wrote:
I find the mathematics is more accurate on
http://www.conservapedia.com
Their facts get checked by the Almighty
It seems you are confusing the notion of counting the number of
operators in the expression with actually evaluating the expression.
Your evalLength function does both.
It may help to consider counting the number of operators in the
expression to be the same as calculating the height of the
A bandaid suggestion:
longFunctionName various and sundry arguments = f where
f | guard1 = body1
f | guard2 = body2
| ...
where declarations
(Disclaimer: untested)
As I understand it, there can be guards on the definition of f even if
it takes no arguments. Those guards can reference your
in this way.
On 7/26/07, Dan Piponi [EMAIL PROTECTED] wrote:
On 7/26/07, Nicolas Frisby [EMAIL PROTECTED] wrote:
Trying to summarize in one phrase: you can do interesting
manipulations to functions before applying fix that you cannot do to
functions after applying fix (conventional functions fall
Whoops, read too fast. Sorry for the noise.
On 7/26/07, Stefan O'Rear [EMAIL PROTECTED] wrote:
On Thu, Jul 26, 2007 at 02:58:21PM -0500, Nicolas Frisby wrote:
A bandaid suggestion:
longFunctionName various and sundry arguments = f where
f | guard1 = body1
f | guard2 = body2
Just casting my vote for the helpfulness of this reference.
Trying to summarize in one phrase: you can do interesting
manipulations to functions before applying fix that you cannot do to
functions after applying fix (conventional functions fall in this
second category).
On 7/26/07, Chung-chieh
Perhaps an information retrieval pipedream, but what if we attempted
an automated FAQ answerer? I'm sure some keywords pop-up often enough
in certain chunks of first posts (heterogenous lists, existential
error messages, SOE and graphics, category functor monad, etc). It
could respond with the
FYI, Gmail *can* kill threads, the Geniuses just deemed it unworthy of
a UI presence. This is news to me and related to earlier comments in
this thread. HTH
http://mail.google.com/support/bin/answer.py?hl=enanswer=47787
On 7/13/07, Nicolas Frisby [EMAIL PROTECTED] wrote:
Perhaps an information
This might be a feasible appropriation of the term destructor.
On 7/10/07, Bruno Oliveira [EMAIL PROTECTED] wrote:
On Tue, 10 Jul 2007 10:53:35 +0200 (MEST), Henning Thielemann wrote:
On Tue, 10 Jul 2007, Tony Morris wrote:
A foldr without recursion. I use such functions frequently in order to
I wrote a combination reader/writer monad (a la the RWS monad in the
mtl) and I find myself wanting to use multiple instances of it in the
same stack of transformers. The functional dependencies prevent this
from working out. The class is called MonadRW and the transformer is
called RWT.
I find
Just a couple of examples: many non-trivial program analyses (like
optimizations or type-inference) rely on viewing the AST as a graph.
Graph reduction is an evaluation paradigm, and I'm guessing that a
(specification-oriented) interpreter might use a graph.
On 6/20/07, Andrew Coppin [EMAIL
I don't know where you got the notion that such structures are not
available in Haskell. There are many efficient data structures in the
libraries. Lists are not magical, just popular, natural, and
traditional. Specialized data structures are always important.
Take a look at the Data.* modules
On 5/27/07, Andrew Coppin [EMAIL PROTECTED] wrote:
[snip]
such that a Reader is created with an initial list, and the read
function fetches 1 element out of that list. That is, the expression x
- read will take the head element of the list and put it into x,
keeping the tail to be read later.
Disclaimer: I've not read the standard.
Sections are de-sugared depending on which argument you supply:
(x^) == (^) x
(^x) == flip (^) x
I think this is why they are considered special cases.
Prelude map (^2) [1..10]
[1,4,9,16,25,36,49,64,81,100]
Prelude map (flip (^) 2) [1..10]
This is a question about some interesting behaviors in GHC's
typechecker regarding MPTCs. The brief code is at the bottom of the
message. By the way, the types can be inferred but not declared
without the forall and ascription in the where clause.
f1 below is illegal because we don't know what
I've had a similar question, which I think boiled down to a
compilation issue. Consider packages A and B that can be defined
independently. But, just as Neil pointed out, perhaps A and B could
also interact beyond their basic definition.
My naive idea is that A would compile the simple
Here here.
This reminds me of a recent discussion on the cafe. Thee OP amounted
to: What are the monad laws good for?. The answer was: It means the
monad doesn't do surprising things and its behavior is congruent with
the basic intuitions of sequenced computation.
In my eyes, proving nice
One technique I find compelling is (ab)using the type class system for
meta programming. Something from Lightweight Static Resources, Faking
It, or Hinze's Full Circle slides might be really attractive. Perhaps
Danvy's Haskell printf? The hook might be:
Yeah, you've heard of strong static typing
[sorry for the double, ajb]
Since there seemed to be a disconnect between the expectation and
the previous answers, I thought an alternative suggestion might help
out. This sort of thing (haha) usually isn't my cup o' tea, so please
point out any blunders.
RM, is this more like what you had in
Both Yitzchak's and my suggestions should run in constant space--some
strictness annotation or switching to foldl' might be necessary.
On 4/12/07, Mark T.B. Carroll [EMAIL PROTECTED] wrote:
Dan Weston [EMAIL PROTECTED] writes:
Ah, but which k elements? You won't know until you've drained your
Using the Endo newtype can avoid such ambiguities:
http://darcs.haskell.org/packages/base/Data/Monoid.hs
newtype Endo a = Endo { appEndo :: a - a }
instance Monoid (Endo a) where
mempty = Endo id
Endo f `mappend` Endo g = Endo (f . g)
Endo allows you to explicitly select the
Section 2.12 of the Parsec manual[1] discusses user state. It sounds
like that is what you are after.
Hope that helps,
Nick
[1] - http://www.cs.uu.nl/~daan/download/parsec/parsec.pdf
On 4/2/07, Joel Reymont [EMAIL PROTECTED] wrote:
Folks,
Are there any examples of keeping a symbol table with
I don't think that
aName =
[ x
, y
, z
]
can be beat for adaptability (i.e. adding/removing/reorganizing
results or _especially_ renaming the declaration). Doesn't do so hot
regarding vertical space though...
On 3/28/07, Greg Buchholz [EMAIL PROTECTED] wrote:
David House wrote:
I see
A wee bit off topic... but bear with me.
Oleg points out a distinction between declaring a class with
functional dependencies and implementing a class with functional
dependencies. Judging from my experience, it might behoove those
wrestling with type classes and FDs to emphasize that the class
Gut feeling: the quick'n dirty script case occurs far less than the
whole module case. Thus I think the benefit of automatically importing
the Prelude if the module declaration is omitted should not happen:
the Principle of Least Surprise out-weighs the small benefit to a rare
case.
Correct me
When I load my program, GHC spits these messages at me, but doesn't
fail Any idea what might be causing this or how to figure that out?
Var/Type length mismatch:
[]
[a{tv aGIf} [tau]]
...
Var/Type length mismatch:
[]
[a{tv aGN8} [tv]]
...
I found the responsible code in GHC's darcs,
Whooops. Thanks for the correction.
On 3/20/07, Levent Erkok [EMAIL PROTECTED] wrote:
On 3/19/07, Nicolas Frisby [EMAIL PROTECTED] wrote:
Nope, but I believe the two are equipotent. This usage of believe is
one of those I think I remember reading it somewhere usages.
On 3/19/07, Henning
In effect, this is a demonstration that Haskell supports recursive
values and not just recursive functions. If the a in
fix :: (a - a) - a
were to be unified always with a function type, then that would imply
that the language only supported recursive definitions for functions,
which would be a
Nope, but I believe the two are equipotent. This usage of believe is
one of those I think I remember reading it somewhere usages.
On 3/19/07, Henning Thielemann [EMAIL PROTECTED] wrote:
On Sat, 17 Mar 2007, Nicolas Frisby wrote:
Bekic's lemma [1], allows us to transform nested fixed points
Bekic's lemma [1], allows us to transform nested fixed points into a
single fixed point, such as:
fix (\x - fix (\y - f (x, y))) = fix f where f :: (a, a) - a
This depends on having true products, though I'm not exactly sure
what that means. Mutual recursion can also be described with
That said, N and R are indeed categories; however, considering them as
categories should be carefully interlaced with your intuitions about
them as types.
I haven't formally checked it, but I would bet that this endofunctor
over N, called Sign, is a monad:
Sign x = x + x
Pos = injectLeft
Neg
Thanks for keeping me honest ;)
On 3/15/07, Dominic Steinitz [EMAIL PROTECTED] wrote:
I haven't formally checked it, but I would bet that this endofunctor
over N, called Sign, is a monad:
Just to be picky a functor isn't a monad. A monad is a triple consisting of a
functor and 2 natural
It seems like we could refine the first parameter of carryPropagate
just as the second: make an= type N1 that only admits values [1..].
Would not that suffice to prove that base is never 0 and not have to
go beyond the type-checker for a proof?
On 3/13/07, Neil Mitchell [EMAIL PROTECTED] wrote:
Which is the longer way of saying you don't need to count to make sure
you closed all the brackets you opened! ;-)
Dougal Stanton
1) Emacs does the counting for me
2) parens don't surprise me if I happen to use rank-2 types.
i was bit enough times when learning why $ and runST don't like
I don't use rank-2 types that often and when I do I'm aware of the
restriction on ($) and similar hofs. I tend to use ($) only when the
right-hand side gets very messy; a multiple-line do or similar. For
example:
blah = fromMaybe $ do
x - blah1
y - blah2
guard (x == f y)
g x
The closing
sum . IntMap.elems . IntMap.IntersectionWith (\x y - x*y) queryVector
rationalProjection
Composition with (.) builds a function, but you eventually want an
Int, so we can't just use (.), but we can come pretty close.
(sum . IntMap.elems . IntMap.IntersectionWith (\x y - x*y)
queryVector)
The deep, dark, Aslan magic of getContents is usually safe to use
because it's a read-only operation. Some of the dangerous corners of
getContents are: what happens if the file is altered while we read it
lazily? This is the sort of question that the sequencing notion of the
IO monad is supposed
This link might be what you are after:
http://okmij.org/ftp/Haskell/typecast.html#deepest-functor
On 3/1/07, Walter Potter [EMAIL PROTECTED] wrote:
Folks,
Given f:: a - b it is very natural to lift f to P f :: P a - P b
where P is the power set functor. Or L f :: [a] - [b].
We are modeling
The type doesn't actually indicate that the type m supports a return
operation. I introduced the qualifier that it was a functor. You
implicity introduced the constraint that it is a monad (actually a
pointed functor, but that's a Monad's return operator). With that
constraint, your thought
Despite the fact that I like head/fromJust etc, a safe list library
would be kind of handy. If someone wants to roll that into the Safe
library, as Safe.List or something, I'd be happy to accept patches
(saving someone else the hassle of setting up a new library etc, for
roughly the same purpose)
I'm still getting my head around this myself, but I know a few
references that might help (maybe not directly, but they're in the
ballpark).
1 I believe the phrase natural lifting or naturality of liftings
is what you're after when you attempt to compare a monad and a bigger
monad that includes
[my mail program hiccuped and chopped my message, sorry]
2 Another example that helped me when getting a feel for reasoning
about monadic code (which is the basis of what we're doing here) was
William Harrison's Proof Abstraction for Imperative Languages. It
uses monads and some of the notions
Here comes an overwhelming post (so stop here if you're not interested
in applicative functors), but apfelmus stepped in this direction. The
funny part is that, modulo dictionary passing (which might be compiled
away), all 6 functions below do the Exact Same Thing because of
newtype erasure
to express very complicated
algorithms in simple and elegant ways, you have to expect to pay a
constant factor (roughly 2x-10x) when competing against the same
algorithm in low-level C.
and this one from Nicolas Frisby,
I have yet to need my Haskell to perform well
Matthew Brecknell came up
http://www.thinkgeek.com/geektoys/cubegoodies/86b8/
Now you can really show your coders why unsafePerformIO is to be avoided!
-Nick
ps - Please don't consider this post a product advertisement or
endorsement of any kind.
___
Haskell-Cafe mailing list
I don't particularly like using fromJust or head, and there's been
plenty of discussion on those issues. For the cases where it makes
good sense to do so, I'm about to write a module for non-empty lists
that looks to strike a balance between usability and static checks.
But before I re-invent the
. 18.19 skrev Nicolas Frisby:
I am very ready for a Haddock that can swallow infix typenames.
Yes, Haddock-GHC can do that.
In dons's recent overview of the last SoC, a darcs repo for Waern's
project was listed. I jumped at the link but couldn't find much
documentation (i.e. the README file
Guess this is a tricky choice for a foldr intro, since it requires a
paramorphism (see bananas lenses wires etc.)
para :: (a - [a] - b - b) - b - [a] - b
para f e [] = e
para f e (x:xs) = f x xs (para f e xs)
-- note that the original tail of the list (i.e. xs and not xs') is
used in the
Oops; I totally forgot the context of this whole discussion!
I enjoyed your article.
On 2/12/07, Bernie Pope [EMAIL PROTECTED] wrote:
Nicolas Frisby wrote:
Guess this is a tricky choice for a foldr intro, since it requires a
paramorphism (see bananas lenses wires etc.)
para :: (a - [a] - b
Very rarely is a nontrivial solution the only way. Monads are a
construct that nicely represents the sequencing side-effecting
computations in a pure and strongly-typed environment. They are a nice
way to do it, but certainly not the only one.
Now I'm not confident enough to boldly make this
A wee bit off topic, but I'm sure it's an acceptable detour.
I just wanted to say that I appreciate both this sort of post and the
consistent responses it solicits. I have yet to need my Haskell to
perform well, but I'm sure that day will come. I like to follow these
questions and hopefully be
There have been some discussions of augmentations of the monad
transformer library. I at least know there was a discussion regarding
strictness of state/value components in the state monad transformer (I
must admit I didn't track the conclusion of that one).
I have another small mtl complaint:
Another option is to use the HList library (though this can involve a
learning curve). Essentially your monad is a state monad and its state
is a big tuple constrained to contain at least whichever types you ask
of it. Consider
foo :: (HOccurs StateA st, ...other HList properties..., MonadState
On the FD impasse:
Witness.hs:33:0:
Couldn't match expected type `m'' (a rigid variable)
against inferred type `RealWitness a a''
`m'' is bound by the type signature for `' at Witness.hs:11:29
When using functional dependencies to combine
Witness WitnessReally a
[Sorry for the duplicate Jeff.]
Is it possible to write a class which checks to see if two given type
arguments are unifiable?
This will probably help:
http://www.haskell.org/pipermail/haskell-cafe/2006-November/019705.html
That was Oleg's response to a post of mine:
Once I start needing to combine Maybe with other monads, I usually
take a moment to generalize the appropriate Maybe parts to MonadError
e m = m. Then we can just use the (ErrorT e IO) monad.
Nick
On 12/16/06, Pepe Iborra [EMAIL PROTECTED] wrote:
Wait, there are two monads in scene here, IO
On 12/14/06, Ross Paterson [EMAIL PROTECTED] wrote:
Absolutely. Some more questions of this type:
How do I update a variable?
How can I efficiently update an array?
How do I get debugging output?
How can I put different types of things in a list?
Sometimes the
Consider the terminal session at the bottom of this message.
The extra xc in Test.hs was the result of me missing CTRL during an
Emacs command (I'm guessing...). Unfortunately this took 30 minutes to
find since I had far more than two modules and the error message
doesn't point this out. Sure
I'm developing a typesafe record library (akin to HList but starting
with key/val pairs and enforcing uniqueness and sorted order of keys).
I'm having a GHC problem I've had with other projects and seen
comments regarding it in other people's code (HList for instance: GHC
doesn't like it's own
As far as I know, the stratified monads are recognized as monad
transformers in Haskell. The predominant library is the Monad
Transformer Library (or mtl) coded by Andy Gill, see [1].
One of my favorite examples of the usefulness of monad transformers is
for building domains for denotational
I have taken the liberty to read into the definition of practical
Haskell; if I'm off target let me know so I can tweak my claims to
fit whatever it is I thought I was discussing ;).
Two cents:
1) This wouldn't be the first book introducing functional programming
to imperative programmers. It
The interpreter infers that m = (e -) because of the types of snd and fst.
When snd and fst are considered as monadic computations in the (e -)
monad, there types are:
Prelude :t fst
fst :: (a, b) - a
Prelude :t snd
snd :: (a, b) - b
Note that: (a, b) - a =~= m awhere m x = (a,b) - x
So
the kind I'm
thinking of. That package has what seems like scary math.
Thanks,
Nick
On 12/8/06, Taral [EMAIL PROTECTED] wrote:
Some of that is in the Ranged Sets library:
http://ranged-sets.sourceforge.net/Ranged/
but it doesn't support Num.
On 12/8/06, Nicolas Frisby [EMAIL PROTECTED] wrote:
I'm
Fantastic!
Just another bit of evidence that Haskell Cafe + one night's sleep can
save a great deal of work. :)
Thanks for pointing that out,
Nick
On 12/8/06, Taral [EMAIL PROTECTED] wrote:
On 12/8/06, Nicolas Frisby [EMAIL PROTECTED] wrote:
I did see that one on the wiki; but it doesn't
I'm looking to not reinvent the wheel.
Is there an existing package that supports interval arithmetic on
integers (or more)? A possible complication is that I'm hoping to
include open intervals such as (GreaterEqThan 3).
If there's not a package to go with, any pointers on the appopriate
rules
It seems there's an assumption about the range of the parameter
function and the range of the entire function. That is, I think we're
assuming that the length of the final result is the same as the length
of the result of the first function?
If I'm correct in presuming that constraint, then I
A agreed upon technique for dealing with typeclass hierarchies has
been slow to arrive. For instance, all monads are functors, but
providing a monad instance for your type doesn't automatically make it
a functor as well.
All monads are also applicative functors, and Control.Applicative does
have
I found nothing in the Gmane archives, so I turn to you. I'm hoping to
Haddock-a-chop my library but the ole infix type constructor (and
there are many of them) is causing a parse error. It seems a common
enough problem, so I was wondering...
1) What ended up happening with David Waern's SoC
Depending on your needs and your comfort level with fancier types, the
existential approach to ADTs might solve your problem. The following
code is a demonstration you can cut-and-paste-and-run.
This is example akin to upcasting in Java to an interface that lets
you print things. That way you
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