[Haskell-cafe] Type problem

[Thomas Davie]

Because applying f to the list is not the same thing is applying bind to the list and f.

Bob

On 26 Feb 2011, at 20:17, michael rice wrote:

> Why? Shouldn't this work for any type a?
> 
> Michael
> 
> ==========
> 
> f :: [a] -> [a]
> f l = do x <- l
>          return x
> 
> ==========
> 
> *Main> :r
> [1 of 1] Compiling Main             ( test.hs, interpreted )
> Ok, modules loaded: Main.
> *Main> f "abcde"
> "abcde"
> *Main> f [1,2,3,4,5]
> [1,2,3,4,5]
> *Main> "abcde" >>= f
> 
> <interactive>:1:12:
>     Couldn't match expected type `Char' against inferred type `m b'
>     In the second argument of `(>>=)', namely `f'
>     In the expression: "abcde" >>= f
>     In the definition of `it': it = "abcde" >>= f
> *Main> 
> 
> 
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