Re: explicit signatures and default for integer literals

Dinko Tenev wrote:

On 5/31/05, Daniel Fischer wrote:

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Why is ghc unable the determine the type of the Literal 0 in the definition of g?

Answer: Since somewhere an instance e.g. New [(a,Double)] (Map a Int) could be defined, leading to problems when threating 0 as (0::Int).

There could be such an instance, but that's obviously not the case. At the point where g is defined, GHC only knows about New [(a,b)] (Map a b), and New [(a,Double)] (Map a Int) doesn't fit.

Consider this:

*Main> :type new . flip zip [0..] new . flip zip [0..] :: (New [(a, b1)] b, Num b1, Enum b1) => [a] -> b

Trying to infer

New [(u, v)] w

out of all that we know, i.e.

New [(a,b)] (Map a b)

should give us

w === Map u v ---> New [(u, v)] (Map u v)

so finally

v === Int ---> New [(u, Int)] (Map u Int)

to infer the context of g.

Is there any good reason not to do this?

Because I'm not smart enough to understand it? ;-)

Cheers,

D. Tenev _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users