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module K.Eval where
import K.Ast
import K.Parsing
import Data.Maybe
isNum Zero = True
isNum (Succ t) = isNum t
isNum _ = False
isVal :: Expr -> Bool
isVal Tru = True
isVal Fals = True
isVal t | isNum t = True
isVal _ = False
eval' x = case x of
IsZero Zero -> Just Tru
IsZero (Succ t) | isNum t -> Just Fals
IsZero t -> IsZero <$> eval' t
Succ t -> Succ <$> eval' t
Pred Zero -> Just Zero
Pred (Succ t) | isNum t -> Just t
Pred t -> Pred <$> eval' t
If Tru t _ -> Just t
If Fals _ f -> Just f
If c t f -> (\c' -> If c' t f) <$> eval' c
_ -> Nothing
nf x = fromMaybe x (nf <$> eval' x)
eval :: Expr -> Maybe Expr
eval t = case nf t of
nft | isVal nft -> Just nft
| otherwise -> Nothing
|
