Re: Code for cond* - cond*-match, cond*-subpat and backtrack-aliases

[Alan Mackenzie <acm@muc.de>]

Hello again, Richard.

On Wed, Jan 24, 2024 at 12:39:54 +0000, Alan Mackenzie wrote:
> On Wed, Jan 17, 2024 at 22:37:47 -0500, Richard Stallman wrote:
> > [[[ To any NSA and FBI agents reading my email: please consider    ]]]
> > [[[ whether defending the US Constitution against all enemies,     ]]]
> > [[[ foreign or domestic, requires you to follow Snowden's example. ]]]

> > Here is the first draft of cond*.  I have tested some cases
> > but I ask others to help in testing it more thoroughly.

> > I invite constructive comments, bug reports, patches,
> > and suggestions.

I've found some more things I'm not happy about in the code.

1/- There are typos in the doc string of cond*-subpat.
2/- There are three places where backtrack-aliases is used where I think
  it should be (cdr backtrack-aliases).
3/- In cond*-subpat, there are bindings for (gensym "ba") which seem
  unable to be referenced by anything.  I think I'm missing something
  here.  As I said yesterday, I'd be happier if gensyms could be
  avoided.  I don't know if this is possible or practicable.
4/- There are several place where "\\>" is appended to a regexp.  Would
  "\\_>" ("end of symbol"), which we've had in Emacs for 10 or 15 years
  now, perhaps be better?

I've included a patch for the first two of these things below.

There are other typos in the code, too, and I think it highly unlikely
that it is bug free, yet.  For cond* to be successful, it will need an
extensive test file.  Possibly we could copy the pcase test file (at
test/lisp/emacs-lisp/pcase-tests.el) and adapt it to cond*.

[ .... ]


--- stallman.20240119.el	2024-01-25 13:31:15.049200457 +0000
+++ stallman.20240125.el	2024-01-25 13:36:44.454224261 +0000
@@ -200,7 +200,7 @@
     ;; Run TRUE-EXPS if match succeeded.  Bind our bindings around it.
     (setq expression
           `(if ,expression
-               ,(if (not (and backtrack-aliases (null uncondit-clauses)))
+               ,(if (not (and (cdr backtrack-aliases) (null uncondit-clauses)))
                     ;; Bind these here if there are no UNCONDIT-CLAUSES.
                     `(let ,(mapcar 'cdr (cdr backtrack-aliases))
                        (let* ,(car raw-result)
@@ -219,7 +219,7 @@
                       (let* ,(car raw-result)
                         ,(cond*-convert uncondit-clauses)))))
     ;; If there are backtrack aliases, bind them around the UNCONDIT-CLAUSES.
-    (if (and backtrack-aliases uncondit-clauses)
+    (if (and (cdr backtrack-aliases) uncondit-clauses)
       (setq expression `(let ,(mapcar 'cdr (cdr backtrack-aliases))
                           ,expression)))
     ;; If we used a gensym, add code to bind it.
@@ -254,16 +254,16 @@
 ;;; ??? Probably should optimize the `nth' calls in handling `list'.
 
 (defun cond*-subpat (subpat cdr-safe bindings backtrack-aliases data)
-  "Generate code to match ibe subpattern within `match*'.
+  "Generate code to match the subpattern within `match*'.
 SUBPAT is the subpattern to handle.
 CDR-SAFE if true means don't verify there are no extra elts in a list.
 BINDINGS is the list of bindings made by
 the containing and previous subpatterns of this pattern.
 Each element of BINDINGS must have the frm (VAR VALUE).
-BACKTRACK-ALIASES is used to pass adta uward.  Initial call should
+BACKTRACK-ALIASES is used to pass data upward.  Initial call should
 pass (list).  The cdr of this collects backtracking aliases made for
 variables boung within (or...) patterns so that the caller
-dna bind them etc.
+can bind them etc.
 DATA is the expression for the data that this subpattern is
 supposed to match against.
 
@@ -290,7 +290,7 @@
              ;; for backtracking, just use that.
              (let ((this-alias (assq subpat (cdr backtrack-aliases))))
                (if this-alias (cdr this-alias)
-                 (if backtrack-aliases
+                 (if (cdr backtrack-aliases)
                      ;; Inside or subpattern but this symbol has no alias,
                      ;; make one for it.
                      (progn (setcdr backtrack-aliases (cons (cons subpat (gensym "ba"))

> > -- 
> > Dr Richard Stallman (https://stallman.org)
> > Chief GNUisance of the GNU Project (https://gnu.org)
> > Founder, Free Software Foundation (https://fsf.org)
> > Internet Hall-of-Famer (https://internethalloffame.org)

-- 
Alan Mackenzie (Nuremberg, Germany).