验证OCaml函数是尾递归 [英] Verify that an OCaml function is tail-recursive

问题描述

如何判断OCaml是否识别特定函数为尾递归？特别是，我想知道OCaml编译器是否识别短路运算符和尾递归

How can I tell if OCaml recognizes a particular function as tail-recursive? In particular, I want to find out if the OCaml compiler recognizes Short-circuited operators and tail recursion

由于Jeffrey的回答如下，我尝试使用简单的函数

Thanks to Jeffrey's answer below, I tried this with the simple function

let rec check_all l =
    match l with
    | [] -> true
    | hd :: tl ->
        hd && check_all tl

而且它的确优化为：

camlTest__check_all_1008:
        .cfi_startproc
.L102:
        cmpl    $1, %eax
        je      .L100
        movl    (%eax), %ebx
        cmpl    $1, %ebx
        je      .L101
        movl    4(%eax), %eax
        jmp     .L102
        .align  16
.L101:
        movl    $1, %eax
        ret

推荐答案

从OCaml 4.03开始，尽管在更改文件，您可以在函数应用程序中使用 @tailcall ，如果不是这样，编译器将发出警告。

Starting from OCaml 4.03, and despite the typo in the Changes file, you can use @tailcall in a function application and the compiler will warn if it is not the case.

（f [@tailcall]）xy 警告如果 fxy 不是尾调用

示例：

$ cat tailrec.ml
let rec f a x = if x <= 1 then a else (f [@tailcall]) (a * x) (x - 1)

let rec g x = if x <= 1 then 1 else x * (g [@tailcall]) (x - 1)

$ ocaml tailrec.ml

File "tailrec.ml", line 3, characters 40-63:
Warning 51: expected tailcall

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