Patrick LeBoutillier patrick.leboutillier at gmail.com writes:
[...]
exprt = Ap (Const mapt) (Const idt)
test = runTI $ tiExpr initialEnv [] exprt
When I execute the test function above in ghci I get:
([],TVar (Tyvar v3 Star)).
I was expecting someting like below for the type
Louis Wasserman wasserman.louis at gmail.com writes:
While working on the Shootout, I noticed the following benchmarks:
http://shootout.alioth.debian.org/u64/program.php?test=chameneosreduxlang=ghcid=3
http://shootout.alioth.debian.org/u64q/program.php?test=chameneosreduxlang=ghcid=3
[...]
Daniel Peebles pumpkingod at gmail.com writes:
My solution attempted to exploit this using Numeric.showIntAtBase but
failed because of the lack of 0 prefixes in the numbers. If you can
find a simple way to fix it without duplicating the showIntAtBase
code, I'd be interested!
Another
Günther Schmidt gue.schmidt at web.de writes:
Hi guys,
I'd like to generate an infinite list, like
[a, b, c .. z, aa, ab, ac .. az, ba, bb, bc ..
bz, ca ...]
If you're happy to have a before the a, you can do this as a fairly cute
one-liner in a similar style to this list of
Andrew Wagner wagner.andrew at gmail.com writes:
I'm sure there's a way to do this, but it's escaping me at present. I
want to do something like this:
data Foo = Bar a = Foo a Bool ...
That is, I want to create a new type, Foo, whose constructor takes
both a Boolean and a value of
Arie Groeneveld wrote:
:
| Looking at the result of my rewriting gives me the idea it isn't
| Haskelly enough.
|
| Anyways, here's my interpretation:
|
| -- period m/n base = (period length, preperiod digits, period digits)
| period :: Integer - Integer - Integer - (Int, ([Integer],
We've seen some nice concise solutions that can deal with the original
problem:
solve 1505 [215, 275, 335, 355, 420, 580]
I'll be a nuisance and bring up this case:
solve 150005 [2, 4, 150001]
A more scalable solution is to use an explicit heap that brings
together all the ways to
*Andrew Coppin wrote:
*
| I'm trying to construct a function
|
| all_trees :: [Int] - [Tree]
|
| such that all_trees [1,2,3] will yield
:
If you write a helper function that takes an N element list, and returns
all 2^N ways of dividing those elements into 2 lists, e.g.
splits ab --
Stefan O'Rear wrote:
| On Mon, Jun 11, 2007 at 09:43:17AM +1000, Thomas Conway wrote:
:
| codeLen 127 = 0
| codeLen 128 = 1
| ...
| codeLen 255 = 8
|
| Now, compiling with ghc 6.6.1 and -O3, I see that it generates a long
| chain of conditional branches.
:
That's deeply tied in
[EMAIL PROTECTED] wrote:
[...]
However, if we try
t2' = W $ id
we get an error:
/tmp/t1.hs:13:
Inferred type is less polymorphic than expected
Quantified type variable `a' escapes
Expected type: (a - a) - b
Inferred type: (forall a1. a1 - a1) - W
In the first argument
Steven Huwig wrote:
On Dec 6, 2004, at 11:05 PM, Tom Pledger wrote:
import Data.Char(isSpace)
import Data.List(groupBy)
(op `on` f) x y = f x `op` f y
wordsAndSpaces = groupBy ((==) `on` isSpace)
`on` is a handy little function in this instance.
Does it have a technical name
Daniel Fischer wrote:
Hi,
I have recently come across the curious phenomenon that ghci is sometimes much
slower than hugs.
[...]
ms as = zipWith (+) (zipWith (*) as (1:ms as)) (0:1:ms as)
Hugs has(**) a specific optimisation for the case where the left hand
side of the declaration occurs as a
Steven Huwig wrote:
[...]
1) Did I miss something in the Prelude or standard library that gives
me this functionality, or something close to it?
[...]
3) The 3-tuple output of unravel looks ugly to me, but I can't think
of an alternative. For the case where there is an equal number of
Keith Wansbrough wrote:
[...]
Your data structure should be something like:
data Interval = Interval {
left :: Double,
leftopen :: Bool,
right :: Double,
rightopen :: Bool
}
data Set = Set [Interval]
If you want more efficiency, you probably want a bintree
MR K P SCHUPKE wrote:
[...]
I dont see why you cannot change the implementation
of lists without changing the interface... Good old lists will
behave like good old lists - just the implementation would try
and take advantage of blocking of the data wherever possible.
Perhaps a pragma to change the
[EMAIL PROTECTED] wrote:
[...]
Actually we merely need to add a deconstructor. Also, we can leave the
type of elements fully polymorphic. Something like this:
class List l where
nil :: l a
cons :: a - l a - l a
decon :: l a
- w -- on empty
- (a - l a - w)
Ron de Bruijn wrote:
--- Martin_Sjögren [EMAIL PROTECTED] wrote:
[...]
mapM_ quickCheck [Test prop_revrev, Test
prop_trivial, Test prop_something]
Regards,
Martin
I didn't expect these replies (including one
mentioning the HList idea(the enforced ordening is
nice, though)), while I tried to be
Brian Smith wrote:
[...]
instance MonadError (Either ReferenceError)
Kind error: `Either ReferenceError' is not applied to enough type
arguments
When checking kinds in `MonadError (Either ReferenceError)'
In the instance declaration for `MonadError (Either ReferenceError)'
MonadError takes
Nathan Weston wrote:
I am learning haskell (and functional programming), from the School of
Expression book.
There's an exercise to rewrite the following function (for computing the area
of a polygon) using map, fold, etc:
data Shape = Polygon [Vertex]
area (Polygon (v1:vs)) = polyArea vs
Hi.
Another way is to take advantage of Haskell's laziness:
class Foo a where
foo :: a - Int
data Oof1 = Oof1 Int
instance Foo Oof1 where foo (Oof1 i) = i
data Oof2 = Oof2 Int
instance Foo Oof2 where foo (Oof2 i) = i
list1 = [foo (Oof1 10), foo (Oof2 20)]
That's all it takes. The applications
Marco Righele wrote:
Hello everyone,
I have some operations that have to be done in sequence, with
each one having the result of the previous as input.
They can fail, so they have signature
a - Maybe b
Checking for error can be quite tedious so I use monadic operations:
f :: a - Maybe b
do
Stefan Holdermans wrote:
Alex,
AG Ignore the layout
AG I can't find the error, running it gives parse error during
AG compile on pStack, it is not very descriptive and I don't
AG what is wrong.
Well, ignoring the layout is not a good thing here, since that's the one of
the causes for your
Georg Martius wrote:
[...]
I could write:
modifyT :: ((a, String) - (a, String)) - a - State String a
modifyT trans a = do str - get
let (a', str') = trans (a, str)
put str'
return a'
f :: State String ()
f = do put hallo
modify strTrans
i -
There are a lot of hoaxes on the internet, but just in case you're for
real, here's an idea...
Step 1: Take 20 minutes to get some fresh air.
Step 2: When you get back to your computer, take 5 minutes to read
Desiderata (http://shell.world-net.co.nz/~unikorn/desiderata.htm),
especially the
Graham Klyne writes:
:
| Ah, yes. I've grown a little wary of foldl, but I see it's
| appropriate in this case. As it's part of the standard prelude, I
| personally have no qualms about depending upon it ... or should I?
(Hope you don't mind my returning this to haskell-cafe.)
Most of
Graham Klyne writes:
:
| Below is some code I have written, which works, but I'm not sure
| that it's especially efficient or elegant. Are there any published
| Haskell libraries that contain something like this?
Hi.
Partially ordered sets are in cahoots with lattices, so you may be
Graham Klyne writes:
:
| What I'd really like to do is assign it to field vbMap, and reference that
| from the definition of vbEnum, but I can't figure out if there's a way
| to do so. Writing this:
| [[
| joinVarBindings vb1 vb2
| | vbNull vb1 = vb2
| | vbNull vb2 = vb1
|
Bayley, Alistair writes:
:
| Still making slow progress on an Oracle database binding... now I'm trying
| to fit the API I have into some sort of abstract interface (like the one(s)
| discussed previously:
| http://haskell.org/pipermail/haskell-cafe/2003-August/004957.html ).
|
|
| 1.
Hi.
The stream of votes has dried up, and the ICFP people and monthly
digest people have had an opportunity, so here's the collated result.
22 people voted.
(A) Give a perfect answer.
(B) Give a subtly flawed answer.
(C) Give an obfuscated answer.
(D) Give a critique of what the questioner has
Hi.
I'm curious about what the people on this list consider appropriate,
as responses to homework questions. Even if there isn't a consensus,
it may be interesting to see how opinion is divided.
Please consider the following.
(A) Give a perfect answer.
(B) Give a subtly flawed answer.
(C) Give
Konrad Hinsen writes:
| On Thursday 21 August 2003 23:23, Jon Cast wrote:
| I can make such a declaration, but it still gets converted to Double.
|
| How are you doing this? I'm not seeing the behavior you describe.
|
| module Foo where
| x = 0.5 :: Fractional a = a
Try
x ::
Tim Docker writes:
:
| Is it normal or common to support multiple simultaneous queries on
| a single DB connection?
In transaction processing, yes. There's an idiom where you use one
query to select all the (financial) transactions in a batch, but
there's so much variation in how you need to
Tim Docker writes:
:
| The list being folded over
| is implied by the DB query, is accessible through the IO monad.
| Hence a parameter is not required. It would really be:
|
| doquery :: Process - String - b - (b - IO (b,Bool)) - IO b
:
| One thing that I am unsure about is whether the
Tim Docker writes:
| Tom Pledger writes:
|
| This is a pretty good way to stop those nasty vague SQL row types at
| the Haskell border and turn them into something respectable. Perhaps
| it would even be worth constraining the extracted type to be in
| DeepSeq
|
| doquery
Thomas L. Bevan writes:
| Does anyone know if there is work being done on a standard Haskell
| database interface.
I suspect that there isn't. The pattern seems to be that someone gets
an interface working well enough for some purposes, and perhaps shares
it, but is too modest and/or busy to
Robert Vollmert writes:
| Hello,
|
| I've been having a little trouble writing a module that waits for and
| handles IO events, e.g. by reading from a pipe. It seemed natural to
| use some form of callbacks here, though that may very well be the
| wrong approach. I'd be happy to hear of
(moving to haskell-cafe)
Alexandre Weffort Thenorio writes:
| Ooops a small error before but here is the right one.
|
| Great. I got almost everything. My problem now is:
|
| I got a function called findstr where
|
| findstr z [,xxxxxx] =
| [z,xxxzxxx]
John Meacham writes:
:
| another useful thing would be
| endOfTime and beginningOfTime constants, representing the minimum and
| maximum values representable by ClockTime.
:
| ___
| Haskell mailing list
| [EMAIL PROTECTED]
|
Tim Otten writes:
:
| Can anyone suggest why the tighter algorithm exhibits significantly
| worse performance? Is takeWhile significicantly more expensive than
| take?
No.
| Is the \z lambda expression expensive?
No.
| The intsqrt isn't recalculated each time takeWhile evalutes a
|
Tom Pledger writes:
| Tim Otten writes:
| :
| | Can anyone suggest why the tighter algorithm exhibits significantly
| | worse performance? Is takeWhile significicantly more expensive than
| | take?
|
| No.
Correction (before anyone else pounces on it):
Only if the predicate function
Scott J. writes:
:
| Sill I want to make objects packed with their objects and
| functions. Doesn't mean that I have to use existential data types?
Sometimes you can avoid using existentials by making all your
object-updating functions return the post-update object explicitly.
For example:
Shawn P. Garbett writes:
:
| What I want is something like this, so that the state transformer has a
| generic state type:
|
| newtype St a s = MkSt (s - (a, s))
|
| apply :: St a s - s - (a, s)
| apply (MkSt f) s = f s
|
| instance Monad St where
| return x = MkSt
From: Cagdas Ozgenc [EMAIL PROTECTED]
| Greetings.
|
| What happens if a type is made an instance of a typeclass in two
| different modules with different implementations?
That's OK, provided that the two instance declarations are never in
scope together, i.e. neither of the modules imports
Joe English writes:
:
| Suppose you have two morphisms f : A - B and g : B - A
| such that neither (f . g) nor (g . f) is the identity,
| but satisfying (f . g . f) = f. Is there a conventional name
| for this?
Is it equivalent to saying that (f . g) is the identity on the range
of f?
Cagdas Ozgenc writes:
| Greetings.
|
| How can I make all types that belong to class A and instance of
| class B, if the implementations of functions in class B can be
| realized by only using the functions in class A?
|
| Thanks for taking time.
Something like this, you mean?
Ludovic Kuty writes:
:
| Is it an idiom or some sort of optimization ?
It's more to do with the particular algorithm for finding the area of
a convex polygon. Try working through the calculation of the area of
this kite.
Polygon [(0, 0), (1, 0), (2, 2), (0, 1)]
I think the two versions
Nguyen Phan Dung writes:
:
| mylist :: [Integer]
| mylist = [1..10]
|
| In Hugs, I type mylist to print out all the elements inside. However,
| after printing about 22000 elements, the system crashs outputs:
| Garbage collection fails to reclaim sufficient memory
The declaration
C T McBride writes:
:
| A little more tinkering, and it looks like it might be
|
| show :: Show (f (Wonky f)) = Wonky f - String
|
| Is this really the type of show?
That looks correct to me.
| If so, no wonder there's a problem.
Yes, there's a vicious circle in context reduction,
Tom Pledger writes:
| C T McBride writes:
| :
| | A little more tinkering, and it looks like it might be
| |
| | show :: Show (f (Wonky f)) = Wonky f - String
| |
| | Is this really the type of show?
|
| That looks correct to me.
Well, after the first context reduction
Mark Wotton writes:
| Hi,
|
| I'm trying out some combinatorial parsers, and I ran into a slightly
| inelegant construction. To parse a sequence of things, we have a function
| like
|
| pThen3 :: (a-b-c-d) - Parser a - Parser b - Parser c - Parser d
| pThen3 combine p1 p2 p3 toks =
|
David Bakin writes:
:
| I have been puzzling over this for nearly a full day (getting this
| reduced version from my own code which wasn't working). In
| general, how can I either a) analyze code looking for a space leak
| or b) experiment (e.g., using Hugs) to find a space leak? Thanks!
Michal Gajda writes:
| On Tue, 29 May 2001, Tom Pledger wrote:
:
| When you consume the (3N)th cell of v, you can't yet garbage collect
| the Nth cell because it will be needed for generating the (3N+1)th,
| (3N+2)th and (3N+3)th.
|
| So, as you proceed along the list, about two
Peter Douglass writes:
:
| but in ( foo ( bar (baz x) ) )
|
| You would want the following I think.
|
| foo . bar . baz x
|
| which does have the parens omitted, but requires the composition
| operator.
Almost. To preserve the meaning, the composition syntax would need to
be
Juan Carlos Arevalo Baeza writes:
:
| First, about classes of heavily parametric types. Can't be done, I
| believe. At least, I haven't been able to. What I was trying to do (as an
| exercise to myself) was reconverting Graham Hutton and Erik Meijer's
| monadic parser library into a
Mark Carroll writes:
| Is this a good place for novice questions?
Yes, either here or on http://haskell.org/wiki/wiki
| greaterthan 0 _ _ = False
| greaterthan _ (x:xs) (y:ys) = x y
:
| Main greaterthan 0 [] []
| ERROR: Unresolved overloading
| *** Type : Ord a = Bool
| ***
Toby Watson writes:
| Intuitively the following scenarios seem to be related, can anyone
| point my in the direction of formal work on this, or give me the
| formal terms I need to search around?
|
| 1. Adding two integers together: Int - Int - Int
|
| 2. Adding two lists of Integers
(moved to haskell-cafe)
G Murali writes:
| hi there,
|
| I'm tryng to get my concepts right here.. can you please help in
| defining a funtion like
|
| makeSet :: (a-Bool)-Set a
|
| I understand that we need a new type Set like
| data Set a = Set (a-Bool) what puzzles me is how to
Konst Sushenko writes:
| what am i missing?
:
| --g :: State String Char
| g = [ x | x - return 'a' ]
Hi.
The comprehension syntax used to be for monads in general (in Haskell
1.4-ish), but is now (Haskell 98) back to being specific to lists.
Does it help if you use do-notation instead?
Marcin 'Qrczak' Kowalczyk writes:
| Fri, 9 Feb 2001 17:29:09 +1300, Tom Pledger [EMAIL PROTECTED] pisze:
|
| (x + y) + z
|
| we know from the explicit type signature (in your question that I was
| responding to) that x,y::Int and z::Double. Type inference does not
| need
Brian Boutel writes:
:
| Having Units as types, with the idea of preventing adding Apples to
| Oranges, or Dollars to Roubles, is a venerable idea, but is not in
| widespread use in actual programming languages. Why not?
There was a pointer to some good papers on this in a previous
Marcin 'Qrczak' Kowalczyk writes:
| On Thu, 8 Feb 2001, Tom Pledger wrote:
|
| nice answer: give the numeric literal 10 the range type 10..10, which
| is defined implicitly and is a subtype of both -128..127 (Int8) and
| 0..255 (Word8).
|
| What are the inferred types for
| f
Dylan Thurston writes:
:
| (A question in the above context is whether the literal '0' should
| be interpreted as 'fromInteger (0::Integer)' or as 'zero'.
| Opinions?)
Opinions? Be careful what you wish for. ;-)
In a similar discussion last year, I was making wistful noises about
Ashley Yakeley writes:
At 2001-01-16 13:18, Magnus Carlsson wrote:
f1 = Just 3
f2 = f3 = f4 = Nothing
So I've declared b = d, but 'theValue b' and 'theValue d' are different
because theValue is looking at the static type of its argument?
What's to stop 'instance TheValue
Manuel M. T. Chakravarty writes:
Lars Henrik Mathiesen [EMAIL PROTECTED] wrote,
From: "Manuel M. T. Chakravarty" [EMAIL PROTECTED]
Date: Fri, 29 Sep 2000 10:17:56 +1100
I agree that usually the predicates as proposed by you would
be better. The problem is that a scanner
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