[Haskell-cafe] Re: Type errors, would extensions help?
gleb.alexeev at gmail.com
Fri Jan 16 04:18:22 EST 2009
> After you pointed my dumb mistake, I was able to build
> the first example -- without any of the extensions! Haskell
> can be misterious some times.
> Strange enough, I can't get the original (and, to my eyes,
> equal) problem to work.
Indeed Haskell can be misterious sometimes. Now that you fixed the typo
the first example compiles, but I think you will be surprised with its
1 % 5
5 % 1
As you can see, the type of printNumber is still monomorphic for the
reasons explained by Ryan Ingram and Lennart Augustsson. It's only the
peculiarity of the numeric classes in Haskell that makes two your
examples different - the constant `5.0' has type `(Fractional t) => t',
and (Ratio a) is an instance of Fractional.
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