Equal (not a token) in an ANTLR grammar. What does this mean?
What does the construct basename =
in the following rule?
tabname:
(ID'.')? basename = ID
;
开发者_如何学JAVAThere is this single occurrence of basename
in the grammar.
Thanks
Using equals in that syntax creates a variable called basename
that can then be referenced in actions:
tabname:
(ID '.')? basename=ID {
if ($basename.equals("CAT"))
System.out.println("CAT found");
};
It is used to name variables.
This can be very useful if you want to run some code during the parser.
Consider the java calculator example:
expr returns [float r]
{
float a,b;
r=0;
}
: #(PLUS a=expr b=expr) {r = a+b;}
| #(STAR a=expr b=expr) {r = a*b;}
| i:INT {r = (float)Integer.parseInt(i.getText());}
;
Here we say when we match a tree that has a PLUS or STAR token followed by 2 expressions, we'll match the expressions and name them a
and b
respectively.
After we'll use those variables we matched in a java statement. This statement is contained inside the {
and }
brackets. Here we use the java statements to actually do the calculation.
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