Haskell中的复数算术表达式

Question

如何在haskell中执行复杂的算术计算？

示例：

eval numb(1) = 1 
eval (add(numb(1),numb(2))) = 3 
eval (add(mult(numb(1),numb(2)),diff(numb(3),numb(4)))) = 1

Answer 1

就像那样，但是有一些轻微的语法调整，所以你说的是GHC的语言。

data Expr = Numb Int | Add Expr Expr | Diff Expr Expr | Mult Expr Expr

eval :: Expr -> Int
eval (Numb x) = x
eval (Add e e') = eval e + eval e'
eval (Diff e e') = eval e - eval e'
eval (Mult e e') = eval e * eval e'

在ghci：

> eval (Numb 1)
1
> eval (Add (Numb 1) (Numb 2))
3
> eval (Add (Mult (Numb 1) (Numb 2)) (Diff (Numb 3) (Numb 4)))
1