Ben schrieb:
dear haskellers --
i'm trying this question again, in haskell-cafe. i got some responses
in haskell-beginners but am looking for more guidance. also, i
understand this functionality is encapsulated in the Workflow module
in hackage, but i'd like to understand this myself.
dear haskellers --
i'm trying this question again, in haskell-cafe. i got some responses
in haskell-beginners but am looking for more guidance. also, i
understand this functionality is encapsulated in the Workflow module
in hackage, but i'd like to understand this myself. this email is an
Yes, the recursive calls of compCommand are supposed to be calls of
compBlock.
The intention of the program is a generic evaluator comp... of
Sigma-terms in arbitrary Sigma-algebras. The signature Sigma is given by
the first 4 types (and the corresponding functions in the class
declaration),
Peter Padawitz wrote:
Yes, the recursive calls of compCommand are supposed to be calls of
compBlock.
The intention of the program is a generic evaluator comp... of
Sigma-terms in arbitrary Sigma-algebras. The signature Sigma is given by
the first 4 types (and the corresponding functions in
On Dec 3, 2007 7:43 AM, Peter Padawitz [EMAIL PROTECTED] wrote:
What is wrong here? ghci tries (and fails) to deduce certain types for
the comp functions that I did not expect.
type Block = [Command]
data Command = Skip | Assign String IntE | Cond BoolE Block Block |
Loop
What is wrong here? ghci tries (and fails) to deduce certain types for
the comp functions that I did not expect.
|type Block = [Command]
data Command = Skip | Assign String IntE | Cond BoolE Block Block |
Loop BoolE Block
data IntE= IntE Int | Var String | Sub IntE IntE |
On Nov 7, 2007 4:34 PM, Nicholas Messenger [EMAIL PROTECTED] wrote:
If you're willing to have an extra Typeable constraint, this does what you
want:
import Data.Typeable (Typeable, cast)
import Data.Maybe (fromMaybe)
toString :: (Show a, Typeable a) = a - String
toString x =
If you're willing to have an extra Typeable constraint, this does what you want:
import Data.Typeable (Typeable, cast)
import Data.Maybe (fromMaybe)
toString :: (Show a, Typeable a) = a - String
toString x = fromMaybe (show x) (cast x)
*Main toString blah
blah
*Main toString 1
1
*Main
Hi folks,
Is there a way to declare a 'toString' function, such that
toString x | x is a String = x
toString x | x's type is an instance of Show = show x
Perhaps, in the type system, there's a way to declare a ToString
class, and somehow inherit all instances of Show as ToString
instances?
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Graham Fawcett
Is there a way to declare a 'toString' function, such that
toString x | x is a String = x
toString x | x's type is an instance of Show = show x
Perhaps, in the type system, there's a way to declare a
On Nov 6, 2007 10:30 AM, Bayley, Alistair
[EMAIL PROTECTED] wrote:
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Graham Fawcett
Is there a way to declare a 'toString' function, such that
toString x | x is a String = x
toString x | x's type is an instance of Show = show x
On 11/6/07, Graham Fawcett [EMAIL PROTECTED] wrote:
ToString.hs:5:0:
Illegal instance declaration for `MyShow String'
(The instance type must be of form (T a b c)
where T is not a synonym, and a,b,c are distinct type variables)
In the instance declaration for `MyShow
I'm assuming you're not fond of the way the print function handles
Strings?
With GHC you can do this:
{-# OPTIONS -fallow-overlapping-instances #-}
{-# OPTIONS -fallow-undecidable-instances #-}
class Show a = MyShow a where show_ :: a - String
instance MyShow String where show_ s =
On Tue, 2007-11-06 at 09:18 -0500, Graham Fawcett wrote:
Hi folks,
Is there a way to declare a 'toString' function, such that
toString x | x is a String = x
toString x | x's type is an instance of Show = show x
Perhaps, in the type system, there's a way to declare a ToString
class, and
Hello,
Have you tried using -fglasgow-exts? That should enable all ghc
extensions.
-Jeff
[EMAIL PROTECTED] wrote on 11/06/2007 02:02:11 PM:
On Nov 6, 2007 12:15 PM, David Benbennick [EMAIL PROTECTED] wrote:
In ghc 6.8.1, the error messages are more helpful:
foo.hs:5:0:
Illegal
On Nov 6, 2007 12:03 PM, Thomas Schilling [EMAIL PROTECTED] wrote:
On Tue, 2007-11-06 at 09:18 -0500, Graham Fawcett wrote:
Hi folks,
Is there a way to declare a 'toString' function, such that
toString x | x is a String = x
toString x | x's type is an instance of Show = show x
I think
On Nov 6, 2007 2:21 PM, Jeff Polakow [EMAIL PROTECTED] wrote:
Have you tried using -fglasgow-exts? That should enable all ghc
extensions.
Ah thanks, that does it.
G
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
On Nov 6, 2007 3:29 PM, Graham Fawcett [EMAIL PROTECTED] wrote:
On Nov 6, 2007 2:21 PM, Jeff Polakow [EMAIL PROTECTED] wrote:
Have you tried using -fglasgow-exts? That should enable all ghc
extensions.
If anyone's interested, I had best results when I added the flag
Tim,
If I have a type class for conversion to a type X:
class XType a where
toX :: a - X
[...]
instance XType String where toX = ...
results in:
Illegal instance declaration for `XType String'
(The instance type must be of form (T a b c)
where T is
On Tue, 22 May 2007, Tim Docker wrote:
I think this must almost be a FAQ, or at least a PAQ (Previously AQ)...
I think it too, thus I added your case to the Wiki:
http://www.haskell.org/haskellwiki/List_instance
___
Haskell-Cafe mailing list
: Tuesday, 22 May 2007 10:11 PM
To: Tim Docker
Cc: haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] type class question
On Tue, 22 May 2007, Tim Docker wrote:
I think this must almost be a FAQ, or at least a PAQ (Previously
AQ)...
I think it too, thus I added your case to the Wiki:
http
I think this must almost be a FAQ, or at least a PAQ (Previously AQ)...
If I have a type class for conversion to a type X:
class XType a where
toX :: a - X
I can define instances for
instance XType Int where toX = ...
instance XType Double where toX = ...
Tim Docker wrote:
I think this must almost be a FAQ, or at least a PAQ (Previously AQ)...
If I have a type class for conversion to a type X:
class XType a where
toX :: a - X
I can define instances for
instance XType Int where toX = ...
instance XType Double
Derek Elkins wrote:
I believe there is a trick where essentially you end up with, instance
IsChar a = XType [a] where ...
That is simple enough, and works fine. Thanks!
Tim
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
24 matches
Mail list logo
