[climacs-devel] Case missing from class regexp's print-object method

[Derek Peschel]

A regexp object may temporarily have a KIND slot of nil, but the print-object
method can't handle that case.  In normal use this doesn't matter, but when
tracing the parsing functions, the debugger tries to call print-object
on fresly-created regexp objects.  So I've taken a stab at a patch, copied
below.

It may be a good idea to create a similar case in the REGEXP-AUTOMATON method
but I don't know what the action of the case should be.

It may also be a good idea to have an output syntax that can't be mistaken
for any legal input.  The real Perl engine, and many clones, first try to
read a quantifier when they see a left brace.  If the read fails they reread
the "quantifier" as a string of literal characters.  If Automaton ever copied
that dubious feature, then my current syntax would become legal input.
So is it best to just choose a new "magic" character or string now?

Or perhaps objects should be intiialized so they print out as "()" or "#"
(without the quotes).

-- Derek



*** regexp.lisp	Sat Aug 27 13:50:55 2005
--- regexp.lisp.new	Sat Aug 27 14:39:25 2005
***************
*** 54,59 ****
--- 54,65 ----
  ;;; non-negative decimal integers and include both end points, and if
  ;;; n and m have the same number of digits, then the conforming
  ;;; strings must have that length (i.e. prefixed by 0's).
+ ;;;
+ ;;; The printout "{nilkind}" denotes a regexp object whose KIND slot
+ ;;; has not been initialized by the parsing routines. Debugging or
+ ;;; tracing can cause such objects to be printed. The language has
+ ;;; no syntax for uninitialized regexp objects and the "{nilkind}"
+ ;;; notation was designed to cause a syntax error when read.
  
  (in-package :automaton)
  
***************
*** 162,167 ****
--- 168,175 ----
  
  (defmethod print-object ((r regexp) s)
    (ecase (kind r)
+     ((nil)
+      (princ "{nilkind}" s))
      (:union
       (princ "(" s)
       (print-object (exp1 r) s)