Template Haskell: reify in GHCi

Question

Is it somehow possible to do reify in GHCi?

When I try it using 'runQ' it complains "can not do reify in the IO monad".

>>> runQ (reify ''Bool)
Template Haskell error: Can't do `reify' in the IO monad
*** Exception: user error (Template Haskell failure)

I'm not looking for :t or something, only for a way to quickly check what reify returns without writing it to a file and loading that file into GHCi.

hammar · Accepted Answer · 2013-05-22 12:27:06Z

31

You just have to run it from a splice instead of using runQ:

> $(stringE . show =<< reify ''Bool)
"TyConI (DataD [] GHC.Types.Bool [] [NormalC GHC.Types.False [],NormalC GHC.Types.True []] [])"

answered May 22, 2013 at 12:27

hammar

140k18 gold badges310 silver badges388 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Frerich Raabe Over a year ago

You can use putStrLn $(stringE . pprint =<< reify ''Bool) to get pretty-printed output.

Hjulle Over a year ago

Is it possible to actually extract the value into a variable, instead of just converting it to a string?

Collectives™ on Stack Overflow

Template Haskell: reify in GHCi

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related