flex lexer - How do you declare this macro in lex? -

i'm new lex , i'm confused on how declare following macro, keyword. want keyword consist of either "if", "then", "else", or "while."

i typed in lex:

keyword                   "if" | "then" | "else" | "while" 

but compiler giving me "unrecognized rule error". when instead do

keyword                   "if" 

it compiles ok.

is limitation of lex? know in jflex can did above , it'll work fine. or doing incorrectly?

thanks

i can't test right now, off top of head:

try putting values in parentheses (before first %%)

keyword                   ("if"|"then"|"else"|"while") 

and use in rules (between %% , %%):

{keyword}   {//action} 

this how make class in lex, in rest of code can use {keyword} , recognized regex you've assigned in definition section (before first %%). also, can use class part of other regexs:

{keyword}\{[^\}]\}   {//action} 

this recognizes whole block of code. (but doesn't check syntax inside block, leave :) )