| The primary goal is to make this part of GHCi. Say, you're working on | a file Foo.hs in your favorite editor, and you have: .... Aha. That is helpful (below). Start a GHC wiki page to describe? Now, if I compile {-# LANGUAGE ImplicitParams #-} module Foo where foo = foldr ?x 'x' [True,False] I get this: Foo.hs:4:13: Unbound implicit parameter (?x::Bool -> Char -> Char) arising from a use of implicit parameter `?x' That looks pretty close to what you want, no? You want the error Foo.hs:4:13: Found a hole of type: Bool -> Char -> Char Same information, with different wording. This reminds me of the recently implemented -fdefer-type-errors. You'd want to be able to *run* a program with hole in it, getting the "unfilled hole of type Bool -> Char -> Char" error if you ever need to evaluate the hole. Anyway, now I understand more clearly what you are trying to do. Thanks. Simon | The primary goal is to make this part of GHCi. Say, you're working on | a file Foo.hs in your favorite editor, and you have: | | --- | | foo = foldr __ 0 [1..5] | | --- | | And you have no idea what you should use at the location of the "__". | You bring up GHCi, and load it as a module: | | $ ghci | GHCi, version 7.5.20120126: http://www.haskell.org/ghc/ :? for help | Loading package ghc-prim ... linking ... done. | Loading package integer-gmp ... linking ... done. | Loading package base ... linking ... done. | Prelude> :load Foo.hs | [1 of 1] Compiling Main ( Foo.hs, interpreted ) | Found a hole at Foo.hs:1:13-14: Integer -> Integer -> Integer | ... | | You notice it needs a function, so you make some more changes and hit | save, so Foo.hs now contains: | | --- | | foo = foldr (\x -> __) 0 [1..5] | | --- | | You reload GHCi, to see if you made progress: | | *Main> :r | [1 of 1] Compiling Main ( Foo.hs, interpreted ) | Found a hole at Foo.hs:1:20-21: Integer -> Integer | ... | | And that's it. It might help IDEs later on, but that is not our goal. | | Regards, | Thijs Alkemade