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| type Val = | |
| | Int of int | |
| | Bool of bool | |
| type Ope = Add | Mul | Lt | |
| type Ast = | |
| | Val of Val | |
| | Form of Ope * Ast * Ast | |
| let exec ope v1 v2 = | |
| match ope, v1, v2 with | |
| | Add, Int x, Int y -> Int (x + y) | |
| | Mul, Int x, Int y -> Int (x * y) | |
| | Lt, Int x, Int y -> Bool (x < y) | |
| let rec eval = | |
| function | |
| | Form (ope, left, right) -> | |
| let (Val leftVal) = eval left | |
| let (Val rightVal) = eval right | |
| Val <| exec ope leftVal rightVal | |
| | x -> x | |
| let form ope a b = Form (ope, a, b) | |
| let integer x = Val (Int x) | |
| let x = | |
| form Add (integer 1) | |
| << form Mul (integer 5) | |
| <| form Add (integer 20) (integer 3) | |
| let (Val (Bool p)) = form Lt (integer 100) x |> eval | |
| stdout.WriteLine p |
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| data Val = Int Int | Bool Bool deriving Show | |
| data Ope = Add | Mul | Lt deriving Show | |
| data Ast = Val Val | Form Ope Ast Ast deriving Show | |
| form :: Ope -> Val -> Val -> Val | |
| form Add (Int x) (Int y) = Int (x + y) | |
| form Mul (Int x) (Int y) = Int (x * y) | |
| form Lt (Int x) (Int y) = Bool (x < y) | |
| red :: Ast -> Ast | |
| red (Form ope left right) = | |
| let Val leftVal = (red left) | |
| Val rightVal = (red right) | |
| in Val (form ope leftVal rightVal) | |
| red x = x | |
| main = do print $ red (Form Lt y x) | |
| where | |
| x = | |
| Form Add (Val (Int 1)) | |
| $ Form Mul (Val (Int 5)) | |
| $ Form Add (Val (Int 20)) (Val (Int 3)) | |
| y = | |
| Val (Int 100) |
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