Question

Suppose I have keyword definitions (case insensitive):

CLASS    (c|C)(l|L)(a|A)(s|S){2}
IF       (i|I)(f|F)
...more....

Now I want to define a KEYWORD which consists of all the keywords:

KEYWORD   (CLASS|IF| ....more....)
IDENTIFIER     [^KEYWORD][a-zA-Z0-9]

However, doing this way, it will only treat CLASS as a string and is not substituted with previous definition. Furthermore,I want to use the KEYWORD definition in IDENTIFIER, is it valid (let’s assume KEYWORD is substituted)?

Answer 1

Ok I found out how to use the previous definition here: http://dinosaur.compilertools.net/flex/flex_6.html#SEC6

We must add {} around the previous definitions:

KEYWORD   ({CLASS}|{IF}| ....more....)
IDENTIFIER     [^{KEYWORD}][a-zA-Z0-9]

I answer myself for future reference from others.