Hello all, We've started a wiki-page discussing how this idea can be applied to GHC here: http://hackage.haskell.org/trac/ghc/wiki/Holes There have already been a number of people who indicated they'd want to use this, so feel free to use the page to leave your comments about how you'd want to use it. Any comments on the best way to implement it are welcome too. We are currently working with the idea of named holes[1], for which we are not using the method mentioned in our earlier mails, but we're working on an implementation more similar to how implicit parameters work. I.e. generating constrains when a hole is encountered, so the same name used multiple times will be inferred correctly. However, these should propagate differently from implicit parameters and should not create an error when the constraint is not in the type signature. Regards, Thijs Alkemade [1] http://hackage.haskell.org/trac/ghc/wiki/Holes#Namedholes