parsing - An explanation of an ANTLR syntax required for JSON grammar -


at moment i'm investigating json antlr grammar antlr project wiki: http://www.antlr.org/wiki/display/antlr3/json+interpreter

string  :     '"' ( escapesequence | ~('\u0000'..'\u001f' | '\\' | '\"' ) )* '"'     ;  fragment escapesequence         :   '\\' (unicodeescape |'b'|'t'|'n'|'f'|'r'|'\"'|'\''|'\\')         ;

what cannot why negate \\ , \" in string rule? matched escapesequence anyway.

if change ~('\u0000'..'\u001f') should mean same.

what missing?

this serves disallowing single unescaped backslashes , single unescaped double quotes. note these appear '\\' , '\"', because @ least former disallowed in grammar literal well.

the escapesequence rule in contrast allows escaped backslashes , double quotes.

omitting exclusion of single unescaped double quote extend string tokenization last quote can found, should terminate @ first unescaped quote.

omitting exclusion of single unescaped backslash allow sequences beginning backslash, not supported escapesequences.


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