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August 28, 2022 08:11
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| {-# LANGUAGE BlockArguments #-} | |
| {-# LANGUAGE LambdaCase #-} | |
| import Control.Monad.State | |
| data Action | |
| = For Expr (Expr -> Action) | |
| | Print Expr | |
| data Expr | |
| = Var String | |
| | Range Int | |
| | Literal Integer | |
| | Mult Expr Expr | |
| instance Num Expr where | |
| (*) = Mult | |
| fromInteger = Literal | |
| interpret :: Action -> String | |
| interpret action = evalState (interpretAction action) 0 | |
| interpretAction :: Action -> State Int String | |
| interpretAction = \case | |
| For seq body -> do | |
| var <- freshVar | |
| body' <- interpretAction (body $ Var var) | |
| pure $ unwords ["for", var, "in", interpretExpr seq, "{", body', "}"] | |
| Print expr -> pure $ "print(" <> interpretExpr expr <> ")" | |
| freshVar :: State Int String | |
| freshVar = state \i -> ("var" ++ show i, i + 1) | |
| interpretExpr :: Expr -> String | |
| interpretExpr = \case | |
| Var v -> v | |
| Range i -> "range(" ++ show i ++ ")" | |
| Literal i -> show i | |
| Mult a b -> "(" ++ interpretExpr a ++ " * " ++ interpretExpr b ++ ")" | |
| program = For (Range 10) \i -> Print (2 * i) | |
| -- $> print $ interpret program | |
| -- "for var0 in range(10) { print((2 * var0)) }" |
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