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{-# LANGUAGE TypeFamilies, NoMonomorphismRestriction #-}
module T2767a where
main = return ()
-- eval' :: Solver solver => Tree solver a -> [(Label solver,Tree solver a)] -> solver [a]
eval' (NewVar f) wl = do v <- newvarSM
eval' (f v) wl
eval' Fail wl = continue wl
-- continue :: Solver solver => [(Label solver,Tree solver a)] -> solver [a]
continue ((past,t):wl) = do gotoSM past
eval' t wl
data Tree s a
= Fail
| NewVar (Term s -> Tree s a)
class Monad solver => Solver solver where
type Term solver :: *
type Label solver :: *
newvarSM :: solver (Term solver)
gotoSM :: Label solver -> solver ()
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