[Haskell-cafe] Beginner question

Benjamin Bach benjaoming at gmail.com
Fri Jan 2 11:57:48 EST 2009

Supposing I have the following code:

> module Main(main) where
>     main = putStr (show [])

I will get these errors from GHC and Hugs respectively:

> Main.hs:2:16:
>     Ambiguous type variable `a' in the constraint:
>       `Show a' arising from a use of `show' at Main.hs:2:16-22
>     Probable fix: add a type signature that fixes these type variable(s)

> ERROR "src/Main.hs":2 - Unresolved top-level overloading
> *** Binding             : main
> *** Outstanding context : Show b

But if I change my code to the following, it will compile.

> module Main(main) where
>     main = putStr (show [1])

I have no problems typing in "putStr (show [])" in Hugs... runs fine.
So what's wrong? I've really tried hard to think of an explanation,
but with no luck..


More information about the Haskell-Cafe mailing list