Hi,
The following code failed to compiled, with error:
Attribute.hs:46:91:
Couldn't match expected type `[t]'
against inferred type `(a, String)'
In the expression: (color_, rest_)
In a case alternative: [(color_, rest_)] - (color_, rest_)
In the expression:
Magicloud Magiclouds magicloud.magiclo...@gmail.com writes:
43 instance Read Attribute where
44 readsPrec _ str = [ (mkAttr attr_ color, rest) | (attr_, rest1) - lex
str
45 , (color, rest) - case
reads rest1 of
46
Hum I must lost my mind
Thank you.
On Mon, Jul 13, 2009 at 3:33 PM, Ketil Maldeke...@malde.org wrote:
Magicloud Magiclouds magicloud.magiclo...@gmail.com writes:
43 instance Read Attribute where
44 readsPrec _ str = [ (mkAttr attr_ color, rest) | (attr_, rest1) - lex
str
45
Brent Yorgey wrote:
Raynor Vliegendhart wrote:
One of the examples I tried was:
hylo (unfoldr (\a - Just (a,a))) head $ 42
This expression fails to determinate.
Here are two examples copumpkin tried on IRC:
copumpkin let hylo f g = g . fmap (hylo f g) . f in hylo (flip
replicate
Hi there,
I'm currently writing an interpreter that I would like to be able to
use with other haskell programs. I would like to be able to pass along
arbitrary types though the interpreter. I've seen hints that GADTs can
do this, but I am having trouble understanding them.
So far, I've learnt
code snippet: no hello world please. That's not a way to judge a
language! But: a random haskell one line snippet with explanation would
be cool.
Perhaps a solution to a problem like the ones you can find on Project
Euler (http://projecteuler.net/index.php?section=problems). Of course
you
Dan Doel wrote:
Hope that helps.
It does, thanks!
Jeremy
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
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Hey Kev,
The types are thrown away during compile time. Therefore, if you
have a constructor VWrapper :: a - Value nothing is known about
that a when you scrutinize it.
What you could do, however, is something like this:
data Value a where
VInt :: Integer - Value Integer
...
On Mon, 13 Jul 2009 12:43:07 +0200, Matthias Görgens
matthias.goerg...@googlemail.com wrote:
code snippet: no hello world please. That's not a way to judge a
language! But: a random haskell one line snippet with explanation would
be cool.
Perhaps a solution to a problem like the ones you
I like the quicksort example at
http://www.haskell.org/haskellwiki/Introduction very much; it shows how much
time you can save when you use Haskell.
Nice idea. Perhaps use a merge sort, because that is actually useful,
because it does not degenerate for large lists.
Matthias.
Hello Matthias,
Monday, July 13, 2009, 6:05:06 PM, you wrote:
I like the quicksort example at
Nice idea. Perhaps use a merge sort, because that is actually useful,
because it does not degenerate for large lists.
Great idea if we want to keep Haskell community compact :)))
--
Best
Nice idea. Perhaps use a merge sort, because that is actually useful,
because it does not degenerate for large lists.
Great idea if we want to keep Haskell community compact :)))
Or stay with quicksort --- which is treesort. :o)
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Then you could add a specific constructor for String. The main point
is: the case construct only works for values, not for types. There is
no typecase construct. If you want to have certain restrictions on the
'a', such as the Show class, you could also do something like this:
data Value
It’s tempting to say, we should
use the original English, which is British English.
Some suggest the original English remained in Britain when the North
American colonies were founded; others claim it was brought to the
Americas by the British settlers, leaving a pale imitation back in
Britain.
Oops, wrong mail account for my last email. Apologies.
What I'm trying to accomplish is being able to write haskell libraries
for the interpreter that don't use the interpreter's predefined Value
types, without having to edit the Value type itself and add a new
constructor (i.e. it's abstracted
On Mon, Jul 13, 2009 at 12:41 PM, Kev
Mahoneymaill...@kevinmahoney.co.uk wrote:
So far, I've learnt you can do this:
data Value where
VInt :: Integer - Value
...
VWrapper :: a - Value
which can let you encode arbitrary 'dynamic' types into Value. I was
hoping to be able to pattern match
Hello Cafe,
I am trying to improve the error reporting in my sendfile library, and I
know I can find out the current file name and line number with something
like this:
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
Unfortunately, if your file is
Thanks, I hadn't noticed Data.Dynamic. It never even occurred to me
that something like this would be in the standard libraries. It looks
like it's precisely what I was looking for, after a brief scan of the
documentation.
I will report back if I bump into any problems with it
2009/7/13 Chaddaï
On Mon, Jul 13, 2009 at 9:18 AM, Kev Mahoneymaill...@kevinmahoney.co.uk wrote:
That said, I think I may defer this until I understand the ins and
outs of Haskell's type system a little better. I think a parametrized
type will be the only way to do it. The only reason I thought GADTs
may be
I am trying to improve the error reporting in my sendfile library, and I
know I can find out the current file name and line number with something
like this:
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
Unfortunately, if your file is in a
Matthew Elder wrote:
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
Unfortunately, if your file is in a hierarchy of folders, this flat file
name doesn't give much context. Is there a macro to find out the current
module? IE if I had a
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
if I had a module Foo.Bar.Car.MyModule, I would like to be able to
output something like this on error:
Foo.Bar.Car.MyModule:2
It works for me. If you place that text in Try/Me.hs and call
On Mon, Jul 13, 2009 at 6:09 AM, Chris Eidhof ch...@eidhof.nl wrote:
Hey Kev,
The types are thrown away during compile time. Therefore, if you have a
constructor VWrapper :: a - Value nothing is known about that a when
you scrutinize it.
What you could do, however, is something like this:
George Pollard schrieb:
Ok, so I have a small idea I'm trying to work on; call it a
Prelude-rewrite if you want. For this I want to be able to have the
hierarchy Functor → Applicative → Monad.
For Functor, I would like to be able to implement it for a wider
variety of types, as there are
Malcolm Wallace wrote:
{-# LANGUAGE CPP #-}
main = putStrLn (__FILE__ ++ : ++ show __LINE__)
This outputs:
test.hs:2
if I had a module Foo.Bar.Car.MyModule, I would like to be able to
output something like this on error:
Foo.Bar.Car.MyModule:2
It works for me. If you place that text
Hello,
is there a working example of how to use the format clause with
HStringTemplate, e.g. for Data.Time.Day? I think, if there is a parameter
$day$, a reasonable template might contain e.g.:
$day;format=%d.%b.%Y$
But I only get toModifiedJulianDay: [54960] as the result which corresponds
It does seem that having quantified contexts would make this *much* easier...
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Hi,
I have a data structure, which shows like this: AttrBgColor {bgColor
= Color 0 0 0}
And the following is my Read code. But it failed parsing
31 instance Read Attribute where
32 readsPrec _ str = [ (mkAttr attr_ color, rest) | (attr_, rest1) - lex str
33
Ryan Ingram wrote:
data Type a where
TInt :: Type Int
TBool :: Type Bool
TChar :: Type Char
TList :: Type a - Type [a]
TFun :: Type a - Type b - Type (a - b)
Type here is what I call a simple type witness. Simple type witnesses
are useful because they can be compared by value,
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