debug segfault

[frontera000]

[root@andLinux ~]# newlisp

newLISP v.9.3.3 on Linux IPv4, execute 'newlisp -h' for more info.



> (define ( x y ) (setq x y ))

(lambda (y) (setq x y))

> (debug (x 1))



-----



(define (x y)

  #(setq x y)#)





[-> 3 ] s|tep n|ext c|ont q|uit > n

Segmentation fault

[root@andLinux ~]#

[cormullion]

Hi!



It's not a debug problem...

Code Select Expand

newLISP v.9.3.2 on OSX IPv4 UTF-8, execute 'newlisp -h' for more info.

> (define (x y) (set 'x y))
(lambda (y) (set 'x y))
>
>
> (x 2)
Bus error


Dunno what's happening there...

[frontera000]

gdb ./newlisp

GNU gdb 6.6-debian

Copyright (C) 2006 Free Software Foundation, Inc.

GDB is free software, covered by the GNU General Public License, and you are

welcome to change it and/or distribute copies of it under certain conditions.

Type "show copying" to see the conditions.

There is absolutely no warranty for GDB.  Type "show warranty" for details.

This GDB was configured as "i486-linux-gnu"...

Using host libthread_db library "/lib/libthread_db.so.1".

(gdb) r

Starting program: /root/newlisp-9.3.3/newlisp

newLISP v.9.3.3 on Linux IPv4, execute 'newlisp -h' for more info.



> (define (x y) (set 'x y))

(lambda (y) (set 'x y))

> (x 2)



Program received signal SIGSEGV, Segmentation fault.

evaluateExpression (cell=0x0) at newlisp.c:1090

1090    if(cell->type & EVAL_SELF_TYPE_MASK) return cell;

(gdb) bt

#0  evaluateExpression (cell=0x0) at newlisp.c:1090

#1  0x08052f4c in evaluateLambda (localLst=0x8080808, arg=<value>,

    newContext=0x80830b0) at newlisp.c:1411

#2  0x0804e8bc in evaluateExpression (cell=0x80805b8) at newlisp.c:1179

#3  0x0805334b in evaluateStream (stream=0xbff35cd4, outDevice=2, flag=0)

    at newlisp.c:946

#4  0x08053a2b in executeCommandLine (command=0xbff35e45 "(x 2)n", outDevice=2,

    cmdStream=0xbff35e2c) at newlisp.c:924

#5  0x080540a9 in main (argc=1, argv=0xbff35ff4) at newlisp.c:732

(gdb) up

#1  0x08052f4c in evaluateLambda (localLst=0x8080808, arg=<value>,

    newContext=0x80830b0) at newlisp.c:1411

1411            result = evaluateExpression(cell);

(gdb) p cell

$1 = (CELL *) 0x0

(gdb) l

1406    /* evaluate body expressions */

1407    cell = localLst->next;

1408    result = nilCell;

1409    while(cell != nilCell)

1410            {

1411            result = evaluateExpression(cell);

1412            cell = cell->next;

1413            }

1414    result = copyCell(result);

1415

(gdb) p nilCell

$2 = (CELL *) 0x807f0a8

(gdb) up

#2  0x0804e8bc in evaluateExpression (cell=0x80805b8) at newlisp.c:1179

1179                                    result = evaluateLambda((CELL *)pCell->contents, args->next, newContext);

(gdb) p *(CELL *)pCell->contents

$3 = {type = 255, next = 0x80807e8, aux = 134738088, contents = 134744040}

(gdb) down

#1  0x08052f4c in evaluateLambda (localLst=0x8080808, arg=<value>,

    newContext=0x80830b0) at newlisp.c:1411

1411            result = evaluateExpression(cell);

(gdb) l 1400

1395    goto GET_LOCAL;

1396

1397    GOT_LOCALS:

1398    /* put unassigned args in $args */

1399    pushEnvironment(argsSymbol->contents);

1400    pushEnvironment((UINT)argsSymbol);

1401    argsSymbol->contents = (UINT)getCell(CELL_EXPRESSION);

1402    if(result != nilCell)

1403      ((CELL*)argsSymbol->contents)->contents = (UINT)result;

1404    ++localCount;

(gdb) p *(CELL*)argsSymbol->contents

$4 = {type = 59, next = 0x807f0a8, aux = 134738088, contents = 134738088}

(gdb)

[Lutz]

The function symbol is modifying itself while executing. The following definition writing 'func' instead of 'x', make this more visible:

Code Select Expand

(defun (func y) (set 'func y))


Self modifying functions are only possible when not setting the symbol but when manipulating the lambda list directly as in:

Code Select Expand

(> (define (func y) (push y func -1))
(lambda (y) (push y func -1))
> (func 99)
99
> func
(lambda (y) (push y func -1) 99)
> (func 99)


This can be used to simulate some kind of closure by redefining parameter defaults:

Code Select Expand

> (define (acc (y 0)) (nth-set (acc 0 0 1) (+ $0 1)))
(lambda ((y 0)) (nth-set (acc 0 0 1) (+ $0 1)))
> (acc)
0
> (acc)
1
> (acc)
2
> (acc)
3
> acc
(lambda ((y 4)) (nth-set (acc 0 0 1) (+ $0 1)))
>


the function always produces the previous value.



ps: see also http://www.alh.net/newlisp/phpbb/viewtopic.php?p=10673&highlight=self+modifying#10673">http://www.alh.net/newlisp/phpbb/viewto ... ying#10673">http://www.alh.net/newlisp/phpbb/viewtopic.php?p=10673&highlight=self+modifying#10673

[frontera000]

i was confused.  too used to clisp still...



# clisp

  i i i i i i i       ooooo    o        ooooooo   ooooo   ooooo

  I I I I I I I      8     8   8           8     8     o  8    8

  I   `+' /  I      8         8           8     8        8    8

     `-+-'  /       8         8           8      ooooo   8oooo

    `-__|__-'        8         8           8           8  8

        |            8     o   8           8     o     8  8

  ------+------       ooooo    8oooooo  ooo8ooo   ooooo   8



Copyright (c) Bruno Haible, Michael Stoll 1992, 1993

Copyright (c) Bruno Haible, Marcus Daniels 1994-1997

Copyright (c) Bruno Haible, Pierpaolo Bernardi, Sam Steingold 1998

Copyright (c) Bruno Haible, Sam Steingold 1999-2000

Copyright (c) Sam Steingold, Bruno Haible 2001-2006



[1]> (defun x (y) (setq x y))

X

[2]> (x 2)

2

[3]> x

2

[Lutz]

Common Lisp uses separate namespaces for function and other variables.