Multiple lex scanners? How?

[Bob Proulx]

Multiple flex generated scanners are giving me trouble with duplicate
symbols.  I am using automake-1.10.

What is the best practice for organizing a program that includes
multiple lex generated scanners?

I am using the recommended practice of using defines to rename all of
the yacc/lex symbols as described in the automake manual
(e.g. "#define yylex c_lex", "#define yyerror c_error", etc.) for the
yacc generated parser.  The problem I encounter is that yyin is hard
to get redefined.  Flex outputs a definition for it before outputing
my define for it in the top of the scan.l file.

Basically what I have looks like this:

  myprog_SOURCES = parse.y scan.l
  BUILT_SOURCES = parse.c parse.h scan.c
  AM_YFLAGS = -d

That is all well and good but then yyin is a global symbol defined by
the flex generated scanner.  This appears before I can redefine it
inside the source.

I guess I can add an AM_CPPFLAGS=-Dyyin=myprogin and list out all of
the symbols to redefine there.  But that fails to work if I have two
flex generated scanners in the same directory.  I would rather find a
more general solution.

If I add an option to flex to rename the symbols like this then the
scanner flex generates renames the symbols for me.

  AM_LFLAGS = -l -Pmyprog

But in this case ylwrap fails because -P also renames the output file
to lex.myprog.c and ylwrap fails to find the produced file.  And it
has the same problem of failing if there are two flex generated
scanners in the same directory.

I am about ready to write a custom rule to sed the generated file.  I
am sure that will work but I must be missing something obvious since
this is a common enough problem that there must be a standard
solution that I am missing.

Thanks
Bob