诡计方案读取行阅读过去的EOF

Question

使用 guile 1.8 或 guile 2，以下代码读取 EOF，似乎多了几行，然后停止。这在作为其摘录的较大程序中的效果是似乎损坏了以前读取的数据。我是否错误地对 eof 对象使用了读取行或测试？

(use-modules (ice-9 rdelim))
(define f
  (lambda (p)
    (let loop ((line (read-line p)))
      (format #t "line: ~an" line)
      (if (not (eof-object? (peek-char p)))
      (begin
        (let ((m (string-match "^[ t]*#" line)))
          (if m
          (begin
              (format #t "comment: ~an" (match:string m))
              (loop (read-line p))
            )))
        (format #t "read next linen")
        (loop (read-line p)))))))
(define main
  (lambda ()
    (let ((h (open-input-file "test")))
      (f h))))

下面是一个最小的示例虚拟输入文件：

1
2
3
# comment line
4
5
1
2
3
# comment line
4
5
1
2
3
# comment line
4
5

它需要超过几行才能使问题显现出来。对于代码示例的长度表示歉意，但问题仅在代码达到这种复杂程度(尽管很小(时才会出现。

Answer 1

我建议重写该过程，这似乎不是读取文件并循环其行的正确方法。请尝试这个：

(define (f)
  (let loop ((line (read-line)))
    (if (not (eof-object? line))
        (begin
          (format #t "line: ~an" line)
          (let ((m (string-match "^[ t]*#" line)))
            (if m (format #t "comment: ~an" line)))
          (format #t "read next linen")
          (loop (read-line))))))
(define (main)
  (with-input-from-file "test" f))

使用示例输入，调用 (main) 会在控制台上打印以下输出，希望这是您所期望的：

line: 1
read next line
line: 2
read next line
line: 3
read next line
line: # comment line
comment: # comment line
read next line
line: 4
read next line
line: 5
read next line
line: 1
read next line
line: 2
read next line
line: 3
read next line
line: # comment line
comment: # comment line
read next line
line: 4
read next line
line: 5
read next line
line: 1
read next line
line: 2
read next line
line: 3
read next line
line: # comment line
comment: # comment line
read next line
line: 4
read next line
line: 5
read next line