Re: [Haskell-cafe] Type checking of partial programs

ac wrote:

foo :: [Foo] -> foo xs = map 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.