小编Éti*_*lon的帖子

我在openssl源代码中注意到一个奇怪的习惯用语,在这里重复如下:

if ((in == NULL) && (passwds == NULL)) {
        if (1) {                                    (* <---- HERE *)
#ifndef OPENSSL_NO_UI
            /* build a null-terminated list */
            static char *passwds_static[2] = { NULL, NULL };

            passwds = passwds_static;
            if (in == NULL)
                if (EVP_read_pw_string
                    (passwd_malloc, passwd_malloc_size, "Password: ",
                     !(passed_salt || in_noverify)) != 0)
                    goto end;
            passwds[0] = passwd_malloc;
        } else {
#endif
            BIO_printf(bio_err, "password required\n");
            goto end;
        }
}

似乎这段代码相当于:

if ((in == NULL) && (passwds == NULL)) {
#ifndef …

我在OCaml中创建monad并需要编写它们,所以我创建了变换器.我使用Identity monad在变换器方面实现了常规monad:

module type MONAD = sig
  type 'a m
  val (>>=) : 'a m -> ('a -> 'b m) -> 'b m
  val return : 'a -> 'a m
end

module Identity : MONAD = struct
  type 'a m = 'a
  let (>>=) m f = f m
  let return x = x
end

module OptionT (M : MONAD) : MONAD with type 'a m := ('a option) M.m = struct
  type 'a m = ('a option) M.m
  let …