CODEWITHSUNDEEP
expressionantlrantlr4symbols
Henrik.A
Henrik.A

Reputation: 31

ANTLR4: Symbols '*' and '+' in the expressions

I am in the process of learning how to program a compiler through antlr. I looked around a bit to get some knowledge about it, so I ended up on this.

What I want to ask is that, what are each symbols doing? The '?', '+' and '*' in the expression, what are they doing?

FLOAT
 : [0-9]+ '.' {_input.LA(1) != '.'}?
 | [0-9]* '.' [0-9]+
 ;

INT
 : [0-9]+
 ;

Do any of you know where to start learning these expressions?

Upvotes: 0

Views: 655

Answers (1)

Roy Cohen
Roy Cohen

Reputation: 1570

These symbols are a part of regular expressions, see this tutorial about regular expression in python (it's very similar in all languages).
the * means match the previous thing zero or more times, for example, a* will match , a, aa, ...
the + means match the previous thing one or more times, for example, a+ will match a, aa, ...
the ? means match the previous thing zero or one times, for example, a? will match or a.

Upvotes: 2

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