haskell - 为什么这个 Haskell 程序中没有使用尾调用优化？

Question

以下程序破坏了堆栈:

__find_first_occurrence :: (Eq b) => b -> [b] -> Int -> Int
__find_first_occurrence e [] i = -1
__find_first_occurrence e (x:xs) i
    | e == x = i
    | otherwise = __find_first_occurrence e xs (i + 1)

find_first_occurrence :: (Eq a) => a -> [a] -> Int
find_first_occurrence elem list =   
    __find_first_occurrence elem list 0

main = do
    let n = 1000000
    let idx = find_first_occurrence n [1..n]
    putStrLn (show idx)

失败

Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it.

但是，据我了解，可能递归调用 __find_first_occurrence是 __find_first_occurrence 评估的最后一件事，因此应该可以进行尾调用优化。

Answer 1

使用尾调用优化，但 (i+1)表达式被 thunked，最后对它们求值会导致堆栈溢出。