CODEWITHSUNDEEP
haskelltemplate-haskell
Gareth Charnock
Gareth Charnock

Reputation: 1166

How do I write a quasi quoter in terms of another quasi quoter

If I'm working with a third party quasi-quoter, for example thirdParty :: QuasiQuoter, and I want to write my own in terms of this quasi-quoter, how do I do this? In ghci I tried

runQ [| [thirdParty| |] |]

But this outputs (in my case):

LamE [VarP _render_2] (AppE (VarE GHC.Base.return) (ConE GHC.Tuple.()))

Which doesn't tell me what the abstract syntax tree for "[thirdParty| |]" is so it seems I can't construct such a patten with template Haskell.

Upvotes: 5

Views: 76

Answers (1)

Gareth Charnock
Gareth Charnock

Reputation: 1166

The answer is face-palmingly simple and I thought of it the moment I finished asking the question. There is nothing magical about QuasiQuoter. It's a plain old boring algebraic data type! Just do:

myQuasiQuoter = QuasiQuoter { quoteExp = f (quoteExp thirdParty) }

Where f is a function that transforms quasi-quoter as required. Do the same thing for quotePat, quoteType, and quoteDec if required.

Upvotes: 5

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