bug#18652: 25.0.50; [PATCH] Add fresh-line

[Leo Liu]

On 2014-10-07 16:45 -0400, Stefan Monnier wrote:
> Oh, I missed this part.  Then, maybe it's OK.  But in the case where
> printcharfun is a function, it should signal an error rather than
> silently returning nil.

How about something like this? Thanks, Leo.

=== modified file 'src/print.c'
--- src/print.c 2014-09-11 06:21:55 +0000
+++ src/print.c 2014-10-08 01:51:45 +0000
@@ -530,6 +530,33 @@
   return Qt;
 }
 
+DEFUN ("fresh-line", Ffresh_line, Sfresh_line, 0, 1, 0,
+       doc: /* Output a newline unless already at the beginning of a line.
+Value is non-nil if a newline is printed.
+Signal an error if PRINTCHARFUN is a function.  */)
+  (Lisp_Object printcharfun)
+{
+  PRINTDECLARE;
+  if (NILP (printcharfun))
+    printcharfun = Vstandard_output;
+  PRINTPREPARE;
+
+  if (FUNCTIONP (printcharfun))
+    signal_error ("Unsupported function argument", printcharfun);
+
+  if (NILP (Fbolp ()))
+    {
+      PRINTCHAR ('\n');
+      PRINTFINISH;
+      return Qt;
+    }
+  else
+    {
+      PRINTFINISH;
+      return Qnil;
+    }
+}
+
 DEFUN ("prin1", Fprin1, Sprin1, 1, 2, 0,
        doc: /* Output the printed representation of OBJECT, any Lisp object.
 Quoting characters are printed when needed to make output that `read'
@@ -2334,6 +2361,7 @@
   defsubr (&Sprinc);
   defsubr (&Sprint);
   defsubr (&Sterpri);
+  defsubr (&Sfresh_line);
   defsubr (&Swrite_char);
 #ifdef WITH_REDIRECT_DEBUGGING_OUTPUT
   defsubr (&Sredirect_debugging_output);