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

[aditya siram]

Ok I've figured out why I can't compile it. But now I'm more confused
than ever. The problem was that I have a -XNoMonomorphismRestriction
flag on Ghci. Removing this allowed me to compile.

But why?

-deech

On Sat, Jan 22, 2011 at 2:07 AM, Magnus Therning <magnus at therning.org> wrote:
> 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
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