我正在尝试实现factorial的尾递归版本:
let{factorial 0 n = n; factorial x n = factorial (x-1, n * x)}
我明白了:
<interactive>:1:41:
Occurs check: cannot construct the infinite type: t1 = t1 -> t1
In the return type of a call of `factorial'
In the expression: factorial (x - 1, n * x)
In an equation for `factorial':
factorial x n = factorial (x - 1, n * x)
<interactive>:1:52:
Occurs check: cannot construct the infinite type: t0 = (t0, t1)
In the first argument of `(-)', namely `x'
In the expression: x - 1
In the first argument of `factorial', namely `(x - 1, n * x)'
<interactive>:1:61:
Occurs check: cannot construct the infinite type: t1 = (t0, t1)
In the second argument of `(*)', namely `x'
In the expression: n * x
In the first argument of `factorial', namely `(x - 1, n * x)'
我如何构建无限类型? (使用GHCi 7.0.1)
答案 0 :(得分:7)
我不是一个强大的Haskell程序员,但我认为你想重写
factorial x n = factorial (x-1, n * x)
作为
factorial x n = factorial (x-1) (n * x)
由于(x-1, n * x)
是一种配对类型,这不是您想要的。
希望这有帮助!