ANTLR Grammar for Recognizing Exponential Notation Numbers and Identifiers

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I’m designing an ANTLR grammar that needs to at least recognize numbers in exponential notation, variable identifiers, and strings. I’m running into an issue where the grammar recognizes 1E4 as if E starts an identifier, instead of recognizing it as a number in exponential notation. I’m testing this on ANTLR Lab (lab.antlr.org).

Here’s the test grammar I’m using:

grammar prueba;

// Parser rules
program : (numeric_constant | identifier)* EOF;

numeric_constant   : sign? number (EXPONENT sign? integer)? ;
number             : integer ('.' integer?)? ;
integer            : DIGIT+ ;
sign               : PLUS_SIGN | MINUS_SIGN ;
identifier         : LETTER (LETTER | DIGIT)* ;

// Lexer rules
EXPONENT           : 'E' ;
PLUS_SIGN          : '+' ;
MINUS_SIGN         : '-' ;
LETTER             : [A-Za-z] ;
DIGIT              : [0-9] ;

And I’m testing it with the input: 1E4, I’m getting the following error:

1:0 mismatched input '1' expecting {, '+', '-', ',', ';'}

Any insights on why it doesn’t recognize 1E4 as a number and how to fix it?

What I tried:

I designed the grammar with the goal of identifying numbers in exponential notation like 1E4. I expected the grammar to recognize 1E4 as a numeric_constant, but instead, it seems to be treating E as the start of an identifier.

What I expected:

Given the input 1E4, I expected it to be parsed as a numeric_constant. However, the parser appears to be treating it as the beginning of an identifier, which isn’t what I intended.

Click on the “Lexer” tab in the top-left in ANTLR Lab and delete the content.

You’re specifying a combined lexer/parser grammar, but that Lexer spec is interfering.

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