[Haskell-beginners] Question about List Type Constraint and Null

[Magnus Therning]

On 22/01/11 06:03, aditya siram wrote:
> Hi all,
> The following function gives me an "Ambiguous type variable `a' in the
> constraint: `Read a' arising from a use of `res'" error:
>   test :: Read a => String -> Maybe [(a,String)]
>   test s = if null res then
>              Nothing
>            else
>              Just $ fst $ head res
>            where
>              res = reads s

This code doesn't give me that error, in fact it gives me no error at all.

/M

-- 
Magnus Therning                      OpenPGP: 0xAB4DFBA4
email: magnus at therning.org   jabber: magnus at therning.org
twitter: magthe               http://therning.org/magnus

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