Re: [Flex-help] I really thank you for your advice. Arthur Schwarz.

[Arthur S. <asc...@at...>]

  I mean that for input streams "abcdefg", I want both pattern /abcd/  and
/bcd/ be active. 
 
  I know that lex/flex generates a token for input streams.
 
  I want multiple tokens be generated simultaneously(concurrently) for
input streams.

1: Token return is a developer concern. That is, flex allows recognition of
a lexeme, the developer provides a return value which is the representative
token.

2: Once /abcd/ is recognized then your choices are:
  a. return two tokens via something like 
     token[0] = value0; 
     token[1] = value1; 
     return token;

  b. backup 3 characters to reread "bcd" and then
     return token = "abcd"
     The caller must now call the lexer to get a token
     For "bcd".

3: The notion of 'active' does not apply. The lexer works by
   Reading an input stream until a pattern is matched, then
   entering the user code for handling the pattern. The user
   code decides on what to do with the pattern once seen. At
   the point that a pattern is being processed, we can say
   that the pattern in 'active', however this is not a 
   common way of addressing that the pattern has been
   accepted.

4: Someone else remarked that once /abcd/ has been accepted, 
   then by default the substring "bcd" is known. As seen in
   2 a) and 2 b) the user code capitalizes on this knowledge
   by generating the appropriate action, in 2 a) two tokens
   are return, in 2 b) one token is returned for "abcd" and
   after a call by the parser, another token is returned for
   "bcd"

5: Since "bcd" is a substring of "abcd" there is no real need
   for there to be two patterns, /abcd/ and /bcd/.

The issue of simultaneity is mystifying. If there is a single caller (the
parser), then that caller usually expects a single response, the return
value(s). Concurrency doesn't arise. If there are multiple tasks and the
lexer supports their activation depending on whether it sees "abcd" or
"bcd" and the desire is to activate two tasks (one for "abcd" and one for
"bcd" then the user code does this by using whatever primitives are
available. But there is no way in C++ to get true simultaneity. The actions
are serial, and even in a multitasking environment, the actions are serial
with pseudo-parallelism accomplished 'concurrently'.

If this is not the answer that suits your problem, please explain your
problem.

art