[Haskell-cafe] Type checking of partial programs

[Don Stewart]

zunino:
> ac wrote:
> > foo :: [Foo] -> <placeholder 1>
> > foo xs = map <placeholder 2> xs
> > 
> > What are the possible type signatures for placeholder 1 and the possible
> > expressions for placeholder 2?
> 
> A nice GHCi trick I learned from #haskell:
> 
> > :t let foo xs = map ?placeholder2 xs in foo
> 
>   forall a b. (?placeholder2::a -> b) => [a] -> [b]
> 
> Also, the djinn tool might provide some actual expression for placeholder 2.
> 
> Zun.

Yes, it turns out implicit parameters provide a great mechanism for
doing type checker queries :)

-- Don