[Haskell-cafe] order of arguments matters

Why does only tr2 work, although the only difference between tr1 and tr2 is the order of arguments? import Data.Tree (Tree(..)) data Type a where Tree:: Type a - Type (Tree a) Int :: Type Int String :: Type String type Traversal1 = forall a.a -

[Haskell-cafe] Set monad

Hi, is there any way to instantiate m in Monad m with a set datatype in order to implement the usual powerset monad? My straightforward attempt failed because the bind operator of this instance requires the Eq constraint on the argument types of m. Peter

[Haskell-cafe] lazy evaluation is not complete

A simplied version of Example 5-16 in Manna's classical book Mathematical Theory of Computation: foo x = if x == 0 then 0 else foo (x-1)*foo (x+1) If run with ghci, foo 5 does not terminate, i.e., Haskell does not look for all outermost redices in parallel. Why? For efficiency reasons? It's

[Haskell-cafe] monad constraint + record update

I'd like to define a monad Set for types in the class Eq. But how can the arguments of Set be constrained when Set is defined as an instance of Monad? instance Eq a = Monad Set where ... obviously cannot work. Is there a standard update function for fields in data types, something that OO

[Haskell-cafe] compilation question

At first a type of arithmetic expressions and its generic evaluator: data Expr = Con Int | Var String | Sum [Expr] | Prod [Expr] | Expr :- Expr | Int :* Expr | Expr :^ Int data ExprAlg a = ExprAlg {con :: Int - a, var :: String - a, sum_ :: [a] - a, prod :: [a] - a, sub

[Haskell-cafe] lazy evaluation

Can anybody give me a simple explanation why the second definition of a palindrome checker does not terminate, although the first one does? pal :: Eq a = [a] - Bool pal s = b where (b,r) = eqrev s r [] eqrev :: Eq a = [a] - [a] - [a] - (Bool,[a]) eqrev (x:s1) ~(y:s2) acc = (x==yb,r) where

[Haskell-cafe] type classes

I'd like to define several instances of the same type class with the same type variable instance. Only method instances differ. How can I do this without writing copies of the type class? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org

Re: [Haskell-cafe] Re: type class question

Jules Bean wrote: Try again without missing out the list... Peter Padawitz wrote: Jules Bean wrote: Incidentally, I question why the compFoo are methods. Why not just make them polymorphic functions? They don't look like you expect instances to change them. The code continues to compile

Re: [Haskell-cafe] Re: type class question

Jules Bean wrote: Peter Padawitz wrote: Jules Bean wrote: Peter Padawitz wrote: What is so bad about making compFoo part of the class? It reduces the code (constraints can be avoided) and reflects the close connection between a signature Sig (implemented by the class

Re: [Haskell-cafe] Re: Re: type class question

-- Prof. Dr. Peter Padawitz Informatik 1 University of Dortmund D-44221 Dortmund Germany phone +49-231-755-5108 fax +49-231-755-6555 secretary +49-231-755-6223 email [EMAIL PROTECTED] internethttp://funlog.padawitz.de

Re: [Haskell-cafe] Re: Re: type class question

Jules Bean wrote: Peter Padawitz wrote: Jules Bean wrote: Peter Padawitz wrote: Functional dependencies don't work in my case. Actually, I don't see why they should. Ah well, it's cruel to say that without explaining to us why! Cause I don't see why the instantiation conflicts

Re: [Haskell-cafe] Re: Re: type class question

Jules Bean wrote: Peter Padawitz wrote: Functional dependencies don't work in my case. Actually, I don't see why they should. Ah well, it's cruel to say that without explaining to us why! Cause I don't see why the instantiation conflicts pointed out by others would vanish then. I'm

Re: [Haskell-cafe] type class question

are the alternatives? Roughly said, I need a construct that allows me gather several type variables such that an instance is always an instance of all of them. On Dec 3, 2007 7:43 AM, Peter Padawitz [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote: What is wrong here? ghci tries

[Haskell-cafe] type class question

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 |

[Haskell-cafe] Graphics.SOE

Can scrollbars be attached to windows created with openWindow? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] lazy patterns versus where-clauses

Is f(~p(x))=e(x) semantically equivalent to: f(z)=e(x) where p(x)=z? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

[Haskell-cafe] Haskell - Tk

Does anybody know O'Haskell or Timber and its interface Tk.hs to Tcl/Tk (see here http://fldit-www.cs.uni-dortmund.de/%7Epeter/tk.html)? I have the following problem: Tk.hs http://fldit-www.cs.uni-dortmund.de/%7Epeter/Tk.hs contains a record (structure) /Canvas/ with selectors line ::

[Haskell-cafe] HGL documentation

Is there a HGL documentation in one volume (e.g. pdf file)? Printing all pieces of http://www.haskell.org/ghc/docs/latest/html/libraries/HGL is a little tedious... Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org

Monad constructors

Why must every Monad instance be a datatype or newtype, even if there will be just a single constructor? Peter ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe

constructors in O'Haskell

How may I hide constructors in O'Haskell 'cause export lists don't work in this language? Peter ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe

Expander2

Expander2: A Formal Methods Presenter and Animator == Expander2 has been designed as a multi-purpose workbench for interactive logical inference, constraint solving, data flow analysis and other procedures building up proofs or computation