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|
{-# LANGUAGE TemplateHaskell #-}
module Bug679 where
import Language.Haskell.TH
data Bar a = Bar
$(do
a <- newName "a"
let classN = mkName "Foo"
let methodN = mkName "foo"
methodTy <- [t| $(varT a) -> $(varT a) |]
let cla = ClassD [] classN [PlainTV a ()] [] [SigD methodN methodTy]
-- Note that we are /reusing/ the same type variable 'a' as in the class
instanceHead <- [t| $(conT classN) (Bar $(varT a)) |]
idCall <- [e| id |]
let ins = InstanceD Nothing [] instanceHead [FunD methodN [Clause [] (NormalB idCall) []]]
pure [cla,ins])
|
