CODEWITHSUNDEEP
haskellghcghc-api
aleator
aleator

Reputation: 4486

Parsing a Type using a GHC-Plugin

I'm working on a compiler plugin that should abort compilation if a declaration doesn't have a type that given as a plugin argument.

I think the function Unify.tcMatchTy :: Type -> Type -> Maybe TCvSubstS would do the trick. I can find one of the argument types from the inputs of the typechecker plugin, but the other comes in as a plugin argument. That is, as a String.

How do I, in a typechecker plugin, get a Type from a String? I tried using parseType followed by calls to rnHsType and tcLHsType, which does convert a String into Type. This seems to work for simple types, but it results in this kind of error when the string contains a type variable:

Text:0:0: error: Not in scope: type variable ‘a’

Text:0:0: error:
    • GHC internal error: ‘a’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: []
    • In the type ‘a -> b’

I'm probably missing some bit (or perhaps a huge chunk) of work here, but where should I look for it?

(Prefixing the input with a forall a b. caused a compiler panic)

Upvotes: 2

Views: 63

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