Re: 3 readline bugs: source positions, readline-options, endless loop on error

[Martin Grabmueller]

> Date: Thu, 25 Jan 2001 13:06:59 +0100 (MET)
> From: Dirk Herrmann <address@hidden>
> 
> On Thu, 25 Jan 2001, Martin Grabmueller wrote:
> 
> > > Date: Thu, 25 Jan 2001 11:41:31 +0100 (MET)
> > > From: Dirk Herrmann <address@hidden>
> > > 
> > > On Thu, 25 Jan 2001, Martin Grabmueller wrote:
> > > 
> > > > The next problem is that with readline, you don't get source positions
> > > > in error messages.  The reason is that the readline port created by
> > > > `make-readline-port' (readline.scm) is not given a file name.  The
> > > > following patch fixes the problem for simple cases, but not when
> > > > calling `set-readline-input-port!', which should also copy the
> > > > filename; but I am not sure how to test this procedure.
> > > > 
> > > > Maybe this problem is not worth fixing anyway, because the filename is
> > > > always `standard input'.
> > > 
> > > I think the problem has to be solved differently:  Why should the output
> > > of source positions be dependent of the existence of a filename for an
> > > input port?  This does not make sense, for example for string ports.
> > > Thus, I suggest to display source positions independent of whether the
> > > port has an associated file name.  If no file name was given, the error
> > > message can use a default string like "<unnamed port>".  Or, rather one
> > > could think of storing the port with the source properties instead of a
> > > filename.
> > 
> > Your first suggestion is easy to implement and only requires hacking
> > display_header in backtrace.c.  I could provide a patch for that.
> 
> Yes, that would be nice.

I started to work on the patch, but I got pretty confused.  Maybe this
is due to my understanding of the term `memoization'.

I take the discussion to guile-devel, so that someone may enlighten me.

It seems that `memoization' is used for two different concepts:

- Rewriting code expressions to a more efficient internal
  representation, like syntax expressions, glocs, ilocs, etc.

- For remembering the positions of source expressions.

So I thought that the macro SCM_MEMOIZEDP indicates whether a source
position has been remembered in the source position hash, and I
changed display_header in backtrace.c to print the filename if that
predicate was true for an expression, and ERROR otherwise.

The new code then tried to print #f as a fixnum, resulting in funny
error messages, until I found out that even expressions without source
positions satisfied the predicate.

With added tests, I got the following patch, but I am not sure whether
it really is The Right Thing.  It enables error positions for readline
and string ports, so it is at least A Useful Thing:

guile> (with-input-from-string "\n\n(asas)" (lambda () (eval (read) 
(interaction-environment))))
<unnamed port>:3:1: In expression (asas):
<unnamed port>:3:1: Unbound variable: asas
ABORT: (unbound-variable)

Patch follows:

Index: backtrace.c
===================================================================
RCS file: /cvs/guile/guile-core/libguile/backtrace.c,v
retrieving revision 1.58
diff -u -r1.58 backtrace.c
--- backtrace.c 2001/01/24 15:58:46     1.58
+++ backtrace.c 2001/01/25 21:46:57
@@ -86,20 +86,25 @@
 static void
 display_header (SCM source, SCM port)
 {
-  SCM fname = (SCM_MEMOIZEDP (source)
-              ? scm_source_property (source, scm_sym_filename)
-              : SCM_BOOL_F);
-  if (SCM_STRINGP (fname))
+  int memoized = SCM_MEMOIZEDP (source);
+
+  if (memoized)
     {
-      scm_prin1 (fname, port, 0);
-      scm_putc (':', port);
-      scm_intprint (SCM_INUM (scm_source_property (source, scm_sym_line)) + 1,
-                   10,
-                   port);
-      scm_putc (':', port);
-      scm_intprint (SCM_INUM (scm_source_property (source, scm_sym_column)) + 
1,
-                   10,
-                   port);
+      SCM fname = scm_source_property (source, scm_sym_filename);
+      SCM line = scm_source_property (source, scm_sym_line);
+      SCM col = scm_source_property (source, scm_sym_column);
+
+      if (SCM_STRINGP (fname))
+       scm_prin1 (fname, port, 0);
+      else
+       scm_puts ("<unnamed port>", port);
+      if (SCM_NFALSEP (line) && SCM_NFALSEP (col))
+       {
+         scm_putc (':', port);
+         scm_intprint (SCM_INUM (line) + 1, 10, port);
+         scm_putc (':', port);
+         scm_intprint (SCM_INUM (col) + 1, 10, port);
+       }
     }
   else
     scm_puts ("ERROR", port);

-- 
Martin Grabmueller              address@hidden
http://www.pintus.de/mgrabmue/  address@hidden on EFnet