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.

score 31 · Accepted Answer · answered May 22 '13 at 12:27

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 '13 at 12:27

hammar

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6

You can use `putStrLn $(stringE . pprint =<< reify ''Bool)` to get pretty-printed output. – Frerich Raabe Aug 16 '14 at 19:44
5

Is it possible to actually extract the value into a variable, instead of just converting it to a string? – Hjulle Jun 03 '16 at 20:23

Template Haskell: reify in GHCi

1 Answers1