Lex: Gather all text not defined in rules - formatting

Question

I'm trying to gather all text that is not defined by a previous rule into a string and prefix it with a formatting string using lex. I'm wondering if there's a standard way of doing this.
For example, say I have the rules:
word1|word2|word3|word4 {printf("%s%s", "<>", yytext);}
[0-9]+ {printf("%s%s", "{}", yytext);}
everything else {printf("%s%s", "[]", yytext);}
And I attempt to lex the string:
word1 this is some other text ; word2 98 foo bar .
I would want this to produce the following when run through the lexer:
<>word1[] this is some other text ; <>word2[] {}98[] foo bar .
I attempted to do this using states, but realize I can't determine when to stop the check, like:
%x OTHER
%%
. {yymore(); BEGIN OTHER;}
<OTHER>.|\n yymore();
<OTHER>how to determine when to end? {printf("%s%s", "[]", yytex); BEGIN INITIAL;}
What is a good way to do this? Is there someway to continue as long as another rule isn't met?

Answer 1

AFAIK, there is no "standard" solution, but a simple one is to keep a bit of context (the prefix last printed) and use that to decide whether or not to print a new prefix. For example, you could use a custom printer like this:
enum OutputType { NO_TOKEN = 0, WORD, NUMBER, OTHER };
void print_with_prefix(enum OutputType type, const char* token) {
static enum OutputType prev = NO_TOKEN;
const char* prefix = "";
switch (type) {
case WORD: prefix = "<>"; break;
case NUMBER: prefix = "{}"; break;
case OTHER: if (prev != OTHER) prefix = "[]"; break;
default: assert(false);
}
prev = type;
printf("%s%s", prefix, token);
}
Then you just need to change the calls to printf to invoke print_with_prefix instead (and, as written, to supply an enum value instead of a string).
For the OTHER case, you then don't need to do anything special to accumulate the token. Just
. { print_with_prefix(OTHER, yytext); }
(I'm skating over the handling of whitespace and newlines, but it's just conceptual.)