Created
May 15, 2018 05:10
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module ShowExpression where | |
data Op = Add | Sub | Mul | Div | |
instance Show Op where | |
show Add = "+" | |
show Sub = "-" | |
show Mul = "*" | |
show Div = "/" | |
valid :: Op -> Int -> Int -> Bool | |
valid Add _ _ = True | |
valid Sub x y = x > y | |
valid Mul _ _ = True | |
valid Div x y = mod x y == 0 | |
apply :: Op -> Int -> Int -> Int | |
apply Add x y = x + y | |
apply Sub x y = x - y | |
apply Mul x y = x * y | |
apply Div x y = div x y | |
data Expr = Val Int | App Op Expr Expr | |
instance Show Expr where | |
show (Val n) = show n | |
show (App o l r) = brak l ++ show o ++ brak r | |
where | |
brak (Val n) = show n | |
brak e = "(" ++ show e ++ ")" | |
values :: Expr -> [Int] | |
values (Val n) = [n] | |
values (App _ l r) = values l ++ values r | |
eval :: Expr -> [Int] | |
eval (Val n) = [n | n > 0] | |
eval (App o l r) = [apply o x y | x <- eval l, | |
y <- eval r, | |
valid o x y] |
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