April 2007 - Hugs-Users

Constraint depth cut off
by Neil Mitchell 20 Apr '07

20 Apr '07

Hi I get the error message: ERROR - *** The type checker has reached the cutoff limit while trying to *** determine whether: *** Typeable (Foo Expr) *** can be deduced from: *** () *** This may indicate that the problem is undecidable. However, *** you may still try to increase the cutoff limit using the -c *** option and then try again. (The current setting is -c100) I find this surprising because in the same file I have: typename_Expr = mkTyCon "Expr" instance Typeable Expr where typeOf _ = mkTyConApp typename_Expr [] typename_Foo = mkTyCon "Foo" instance Typeable1 Foo where { typeOf1 _ = mkTyConApp typename_Foo [] } instance Typeable a => Typeable (Foo a) where { typeOf = typeOfDefault } I then went even further, giving it an explicit instance with: instance Typeable (Foo Expr) where And still I get the same error message. I originally had -c40 (default), but bumping it up has no effect. Any idea what may be causing this? Thanks Neil

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isPrime definition
by Alex Teslin 18 Apr '07

18 Apr '07

Hi, I am a newbie in Haskell and have a trivial question. I am using Simon Thomson's textbook for learning Haskell with Hugs. I am stack with exer 5.10, which asks to define isPrime function using divisors function previously defined. I have managed to define the divisor function like this: divisors :: Int -> [Int] divisors n = [x | x<-[1..n], n `mod` x == 0] but when i am trying with isPrime function using divisors and list comprehension - i am lost because the type signature should be isPrime :: Int->Bool But any list comprehension generates a list, which is not what i want. Any suggestions please? Thank you --------------------------------- Yahoo! Answers - Got a question? Someone out there knows the answer. Tryit now.

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list vs. atom
by aminagho 10 Apr '07

10 Apr '07

what is the best way to distinguish atoms and lists in haskell? I mean How I can find out the variable is List or atom. I know we can use :t to define type but I cannot use this. I have to do it dynamically in my program. Thanks a lot for your attention. -- View this message in context: http://www.nabble.com/list-vs.-atom-tf3543626.html#a9892551 Sent from the Haskell - Hugs-Users mailing list archive at Nabble.com.

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