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module Typecheck
(inferExpr,
checkExpr)
where
import Syntax
import Control.Monad
type Environment = [(Idnt,Typ)]
assertInt TInt = Just ()
assertInt _ = Nothing
assertRec (TRecord ts) = Just ts
assertRec _ = Nothing
assertVar (TVariant ts) = Just ts
assertVar _ = Nothing
assertPtr (TPtr t) = Just t
assertPtr _ = Nothing
inferExpr :: Expr -> Environment -> Maybe Typ
inferExpr (Var name) env = lookup name env
inferExpr (IntLit _) _ = Just TInt
inferExpr (Record _) _ = undefined
inferExpr (Variant t v e) env = do
ts <- assertVar t
tt <- lookup v ts
checkExpr e env tt
return t
inferExpr (Add e1 e2) env = do
checkExpr e1 env TInt
checkExpr e2 env TInt
return TInt
inferExpr (Mult e1 e2) env = do
checkExpr e1 env TInt
checkExpr e2 env TInt
return TInt
inferExpr (Neg e) env = do
checkExpr e env TInt
return TInt
inferExpr (Deref e1) env = do
t <- inferExpr e1 env
tt <- assertPtr t
return tt
checkExpr :: Expr -> Environment -> Typ -> Maybe ()
checkExpr e env t = do
t' <- inferExpr e env
guard (t==t')
return ()
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