Many languages bound a string with some sort of quote, like this:
"Rob Malda is smart."
ANTLR 4 can match such a string with a lexer rule like this:
QuotedString : '"' .*? '"';
To use certain characters within the string, they must be escaped, perhaps like this:
"Rob \"Commander Taco\" Malda is smart."
ANTLR 4 can match this string as well;
EscapedString : '"' ('\\"|.)*? '"';
(taken from p96 of The Definitive ANTLR 4 Reference)
Here's my problem: Suppose that the character for escaping is the same character as the string delimiter. For example:
"Rob ""Commander Taco"" Malda is smart."
(This is perfectly legal in Powershell.)
What lexer rule would match this? I would think this would work:
EscapedString : '"' ('""'|.)*? '"';
But it doesn't. The lexer tokenizes the escape character " as the end of string delimiter.
Negate certain characters with the ~ operator:
EscapedString : '"' ( '""' | ~["] )* '"';
or, if there can't be line breaks in your string, do:
EscapedString : '"' ( '""' | ~["\r\n] )* '"';
You don't want to use the non-greedy operator, otherwise "" would never be consumed and "a""b" would be tokenized as "a" and "b" instead of a single token.
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