one weird trick to get all your types

Richard Eisenberg eir at
Wed Nov 11 18:03:13 UTC 2015

Hi devs,

I spent some of my time at Hac Phi this past weekend teaching a few people the ropes about GHC hacking. One innocently asked if it's possible to load GHC into GHCi. I shuddered at the thought. But, actually, you can get quite close to this ideal:

> ghc-stage2 --interactive
GHCi, version 7.11.20151104:  :? for help
Prelude> :set -package ghc         -- THIS IS THE KEY LINE
package flags have changed, resetting and loading new packages...
Prelude> import TcMType
Prelude TcMType> :t newEvVar
  :: forall gbl lcl.
     TcType.TcPredType -> TcRnTypes.TcRnIf gbl lcl Var.EvVar
Prelude TcMType> 

Pretty cool, huh? This improves my life. Hopefully it improves yours, too.


PS: Can anyone recommend a place on the wiki where I should put this?

More information about the ghc-devs mailing list