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Token Alias Bug

From: Baum, Nathan I
Subject: Token Alias Bug
Date: Tue, 25 Sep 2001 15:46:13 +0100

I've noticed a bug in bison. Sadly, our eternally wise sysadmins won't let
us use CVS, so I can't find out if it's been fixed already...

Basically, I made a program (in flex) that went through a .y file looking
for "..."-tokens, and then outputed a %token
line for it. For single-character ""-tokens, I reasoned, I could just use
[%token 'A' "A"]. However, this causes Bison to output a [#define 'A' 65],
which cppp chokes on, not unreasonably. (And even if cppp didn't choke, I
obviously wouldn't want (char)'A' to be replaced with (int)65 throughout my

Bison normally forgoes outputing a #define for a character token. However,
it always outputs an aliased token -- even if the token is an alias for a
character token. We don't want that. The problem is in /output.c/, as I
recall. When it outputs the token definitions, it checks for a character
token, and then checks for an alias token. If the character token check is
placed after the alias check, then it works correctly.

Alias tokens seem to be something of a kludge. What about an [%alias "..."]

        %alias T_IF "IF"

Hmm. I can't help thinking... What about a --generate-lex option that
creates an .l file for the alias tokens used... (Or an option to make a
gperf file, etc...)


I've also noticed something, that whilst not *wrong*, is inconvienient: I
use the verbose mode to help find the causes of unresolved shift/reduce
conflicts. However, this mode insists on starting the .output file with a
list of *resolved* conflicts, something I find quite useless. Might it be
possible to define a -v mode, and a -vv mode -- Where the -vv mode shows
everything, but the -v mode only tells you what you need for examining
conflicts? (Or, perhaps, a "*** This state has N conflicts ***" marker above
each state with conflicts.)

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