> One difficulty is that many of the core type data types, e.g. TyThing, > are (1) a large mutually recursive graph, and (2) have > unsafeInterleaveIO thunks which would induce IO action. So a naive > Show instance would give infinite output and have lots of side effects. > There are many data types which could usefully have Show added but > also many which would be very difficult to.
Ah, yes, this is a very annoying problem. I discovered that when I first wrote CoreDump: https://github.com/osa1/CoreDump/issues/2 I don't have solution to this yet. 2015-10-19 21:59 GMT-04:00 Edward Z. Yang <ezy...@mit.edu>: > Excerpts from Ömer Sinan Ağacan's message of 2015-10-19 14:18:41 -0700: >> I was wondering what would be the cost of adding Show instances. Would that >> mean significantly increased compile times? Or significantly bigger GHC >> binaries? If that's the case, could we enable Show instances with some >> arguments so that we can enable/disable it by modifying mk/build.mk? > > One difficulty is that many of the core type data types, e.g. TyThing, > are (1) a large mutually recursive graph, and (2) have > unsafeInterleaveIO thunks which would induce IO action. So a naive > Show instance would give infinite output and have lots of side effects. > There are many data types which could usefully have Show added but > also many which would be very difficult to. > > Edward _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
