CODEWITHSUNDEEP
regexjavacc
Alex R
Alex R

Reputation: 41

Javacc excluding tokens

I have the following piece of code and would like to exclude reserved words as identifiers in the | < ID : ()+("_")(<#DIGIT>)()* > . I understand that I can match one or more, zero or more but how can I possible exclude something from a regular expression. Any guidance would be greatly appreciated. 

TOKEN : /* Numbers and identifiers */
{
< INT : (<DIGIT>)+ >
| < #DIGIT : ["0" - "9"] >
| < ID : (<LETTER>)+("_")*(<#DIGIT>)*(<LETTER>)* >
| < #LETTER : ["a" - "z", "A" - "Z"] >
}


TOKEN : { /* RESERVED WORDS  */ 
 <VARIABLE: "variable">
|  <CONSTANT: "constant">
|  <RETURN: "return">
|  <INTEGER: "integer">
|  <BOOLEAN: "boolean">
|  <VOID: "void">
|  <MAIN: "main">
|  <IF: "if">
|  <ELSE : "else">
|  <TRUE: "true">
|  <FALSE: "false">
|  <WHILE: "while">
|  <BEGIN: "begin">
|  <END: "end">
|  <IS: "is">
|  <SKIP: "skip">
}

Upvotes: 2

Views: 503

Answers (1)

Theodore Norvell
Theodore Norvell

Reputation: 16221

When two regular expressions both match the longest match, the first one wins. (See the JavaCC FAQ.)

So the solution is easy: Reorder the productions:

TOKEN : { /* RESERVED WORDS  */ 
   <VARIABLE: "variable">
|  <CONSTANT: "constant">
|  <RETURN: "return">
|  <INTEGER: "integer">
|   ...
}

TOKEN : /* Numbers and identifiers */
{
  < INT : (<DIGIT>)+ >
| < #DIGIT : ["0" - "9"] >
| < ID : (<LETTER>)+("_")*(<#DIGIT>)*(<LETTER>)* >
| < #LETTER : ["a" - "z", "A" - "Z"] >
}

Upvotes: 2

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