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latest port-line fix.

I see the latest anoncvs source tree has (in genio.c):

   char *
   scm_do_read_line (port, len)
	SCM port;
	int *len;
     char *s;
     scm_sizet i;

     i = SCM_PTOBNUM (port);
     SCM_SYSCALL (s = (scm_ptobs[i].fgets) (port, len));

     /* If we're not at EOF, and there was a newline at the end of the
	string, increment the line counter.  */
     if (s && *len > 0 && s[*len - 1] == '\n')

     return s;

If the *len > 0 is necessary then scm_read_line (in ioext.c) has a
bug in:

  s = scm_do_read_line (port, &slen);

  if (s == NULL)
    term = line = SCM_EOF_VAL;
      if (s[slen-1] == '\n')
          term = SCM_MAKICHR ('\n');
          line = scm_makfromstr (s, slen-1, 0);
          /* Fix: we should check for eof on the port before assuming this. */
          term = SCM_EOF_VAL;
          line = scm_makfromstr (s, slen, 0);
      free (s);

i.e. - the code in ioext.c implies that if scm_do_read_line, & hence
scm_ptobs[i].fgets doesn't return null then length is >0, which makes

In other words, there're 2 cases:

1. fgets reads a character - then it's in the returned string & len>0.
2. fgets doesn't read a character - then it returns null.

I could see why you'd want the extra insurance test, but I'd be afraid
of making the code self-inconsistent.  Someone might reason about
what fgets can or should return based on the code in genio.c & then
break the code in ioext.c, or might decide there's a bug in ioext.c &
add the additional test, ...

Or do you have other reasons for the extra test?

Harvey J. Stein
BFM Financial Research