相关疑难解决方法(0)

我写了这段代码,我假设len是尾递归,但仍然会发生堆栈溢出.怎么了？

myLength :: [a] -> Integer

myLength xs = len xs 0
    where len [] l = l
          len (x:xs) l = len xs (l+1)

main = print $ myLength [1..10000000]