| After reading the paper "Pattern Guards and Transformational Patterns" | by Martin Erwig and Simon Peyton Jones, I'm left wondering about the | status of transformational patterns? Can we expect to see these at | some point in GHC? Or have they gone by the wayside in favor of some | other alternative? | | When I had finished reading the paper, I was disappointed to find out | that they were not implemented as I was convinced of the merits based | on the arguments presented in the paper. We have no immediate plans to add views or transformational patterns to GHC. Why not? a) we already have pattern guards http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.htm l#pattern-guards which do part of the job b) in any language, there is a trade-off between complexity and expressiveness. It's not immediately clear which side of the line views lie. c) there are a number of alternative designs, and no clear winner Having said that, I think one can make a strong case that some form of views support is essential to allow abstraction, and that views should therefore have direct support. Indeed, it's on the table for Haskell Prime http://hackage.haskell.org/trac/haskell-prime/wiki/Views It would be a Good Thing, I believe, if those interested in views and/or transformational patterns could use the above Wiki to record the various possible designs, and try to converge on one. Then it might be an interesting intern project to implement it: http://hackage.haskell.org/trac/ghc/wiki/Internships Simon