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From: Andrew Klaassen <clawsoon@my-dejanews.com>
Newsgroups: comp.lang.beta
Subject: Virtual attribute gives Seg Fault when accessed from pattern ref
Date: Sun, 02 May 1999 18:45:39 GMT
Organization: Deja News - The Leader in Internet Discussion
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Greetings:

I don't have a great handle on all of BETA's 'big words' (it
took me half an hour just to find the words I needed for my
subject line <G>), so I'll have to explain my question with
code. The first program below compiles and runs. The second
program compiles, but crashed with a 'Segmentation Fault' at
the indicated point.  Why?

The first program:

ORIGIN '~beta/basiclib/v1.6/betaenv';
---program:descriptor---
(* This program compiles and runs. *)
(#

Function: (* a simple pattern *)
  (# a: @integer;
     Printname: (# do 'Function' -> putline; #);
    enter a
    do
      a -> putint; newline;
  #);

PatRef: ##Function;

do

  Function## -> PatRef##;
  3 -> PatRef;
  PatRef.Printname;

#)

The second program, which is very similar to the first:

ORIGIN '~beta/basiclib/v1.6/betaenv';
---program:descriptor---
(* compiles but crashes *)
(#

Function:
  (# a: @integer;
     (* Printname is now a virtual pattern *)
     Printname:< (# do inner #);
    enter a
    do
      a -> putint; newline;
  #);

(* And we have a subpattern of Function, F1, which does
   a final binding on Printname. *)
F1: Function (# Printname:: (# do 'Function' -> putline; #); #);

PatRef: ##Function;

do

  F1## -> PatRef##;
  3 -> PatRef; (* works *)
  PatRef.Printname; (* crashed the program with a
                       'Segmentation Fault' *)

#)

I'm not very familiar with the use of ## - there aren't many
references to it in the BETA Language Intro, Tutorial, FAQ, etc -
so I might be using it incorrectly.  If anyone could explain
what's happening when the second program tries to execute
PatRef.Printname, it would be much appreciated.

Thanks!

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