むらけんです.

メソッド定義やクラス定義の中で定数への代入演算を行うと core を
吐きます.

[muraken@dirac muraken]$ ruby -e "AHI=2; def a; ::AHI+=3; end"
-e:1: constant re-assignment
AHI=2; def a; ::AHI+=3; end
                       ^
-e:1: [BUG] Segmentation fault
ruby 1.8.1 (2003-12-23) [i686-linux]

Aborted (core dumped)
[muraken@dirac muraken]$ gdb ruby core.18415
GNU gdb 5.3
Copyright 2002 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 "i586-momonga-linux"...
(no debugging symbols found)...
Core was generated by `ruby -e AHI=2; def a; ::AHI+=3; end'.
Program terminated with signal 6, Aborted.
Reading symbols from /usr/local/cvs-ruby/lib/libruby.so.1.8...done.
Loaded symbols for /usr/local/cvs-ruby/lib/libruby.so.1.8
Reading symbols from /lib/libdl.so.2...done.
Loaded symbols for /lib/libdl.so.2
Reading symbols from /lib/libcrypt.so.1...done.
Loaded symbols for /lib/libcrypt.so.1
Reading symbols from /lib/libm.so.6...done.
Loaded symbols for /lib/libm.so.6
Reading symbols from /lib/libc.so.6...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/libpthread.so.0...done.
Loaded symbols for /lib/libpthread.so.0
Reading symbols from /lib/ld-linux.so.2...done.
Loaded symbols for /lib/ld-linux.so.2
#0  0x40155931 in kill () from /lib/libc.so.6
(gdb) where
#0  0x40155931 in kill () from /lib/libc.so.6
#1  0x4025dbfc in pthread_kill (thread=18415, signo=1076183884) at signals.c:65
#2  0x4025df45 in __pthread_raise (sig=6) at signals.c:187
#3  0x401556f5 in *__GI_raise (sig=1076258708)
    at ../linuxthreads/sysdeps/unix/sysv/linux/raise.c:34
#4  0x40156beb in *__GI_abort () at ../sysdeps/generic/abort.c:88
#5  0x40031884 in rb_bug (fmt=0x400b9744 "Segmentation fault") at error.c:199
#6  0x4008dd9f in sigsegv (sig=11) at signal.c:419
#7  0x402613fd in __pthread_sighandler (signo=11, ctx=
      {gs = 0, __gsh = 0, fs = 0, __fsh = 0, es = 43, __esh = 0, ds = 43, __dsh = 0, edi = 0, esi = 10193, ebp = 3221222472, esp = 3221222448, ebx = 1074512580, edx = 3221222656, ecx = 1, eax = 1074187394, trapno = 14, err = 4, eip = 1074215006, cs = 35, __csh = 0, eflags = 66054, esp_at_signal = 3221222448, ss = 43, __ssh = 0, fpstate = 0xbffff1b0, oldmask = 2147483648, cr2 = 10193})
    at sighandler.c:38
#8  <signal handler called>
#9  newline_node (node=0x27d1) at parse.y:4453
#10 0x4006cc93 in ruby_yyparse () at parse.y:383
#11 0x4006ff6e in yycompile (f=0x400b9391 "-e", line=1) at parse.y:2541
#12 0x4008c5ea in proc_options (argc=0, argv=0xbffffcd0) at ruby.c:773
#13 0x4008d838 in ruby_process_options (argc=3, argv=0xbffffcc4) at ruby.c:1115
#14 0x400354a2 in ruby_options (argc=3, argv=0xbffffcc4) at eval.c:1351
#15 0x08048ad5 in main ()
---Type <return> to continue, or q <return> to quit---
#16 0x40142fec in __libc_start_main (main=0x8048aa0 <main>, argc=3, 
    ubp_av=0xbffffcc4, init=0x8048dc0 <__libc_csu_init>, 
    fini=0x8048e10 <__libc_csu_fini>, rtld_fini=0x40013020 <_rtld_local>, 
    stack_end=0x40266794) at ../sysdeps/generic/libc-start.c:225
(gdb) 

-- 
1024D/2A3FDBE6 2001-08-26 Kenta MURATA (muraken) <muraken2 / nifty.com>
Key fingerprint = 622A 61D3 280F 4991 4833  5724 8E2D C5E1 2A3F DBE6