kit

json_frontend.ebnf (2185B)

---

 // JSON front end: the realistic JSON grammar (RFC 8259) with the two sub-lexers
 // a real frontend uses to turn leaf lexemes into values. The parser yields whole
 // NUMBER / STRING tokens; the value-channel actions then point a sub-lexer at the
 // token's own bytes to decode it — NUMBER via the `number` sub-lexer (classify
 // int vs float, read the integer value), STRING via the `strescape` sub-lexer
 // (unescape into raw UTF-8). Driven by test/realistic/test_json_frontend.c, which
 // reaches the sub-lexers through gramgen_lexer_grammar_at / gramgen_find_lexer.
 //
 // The main lexer + parser are the ordinary JSON grammar, written with inline
 // string literals ("[", "true", ...) exactly like test/realistic/json.ebnf — the
 // `strescape` sub-lexer's catch-all SCHARS = [^"\\]+ does NOT shadow them, because
 // parser literals are scoped to the parser-feeding (main) lexer and never
 // injected into a sub-lexer.
 %lex {
   %skip WS = [ \t\r\n] [ \t\r\n]*;
 
   // string = quote ( unescaped | '\' escape )* quote
   STRING = "\"" ( [^"\\] | "\\" ( ["\\/bfnrt] | "u" [0-9A-Fa-f] [0-9A-Fa-f] [0-9A-Fa-f] [0-9A-Fa-f] ) )* "\"";
 
   // number = -? int frac? exp?    (no leading zeros, per the spec)
   NUMBER = "-"? ( "0" | [1-9] [0-9]* ) ( "." [0-9]+ )? ( [eE] [+\-]? [0-9]+ )?;
 }
 
 // NUMBER payload -> sign / integer / fraction / exponent parts.
 %lex number {
   %def digit = [0-9];
   NSIGN = "-";
   NINT  = digit+;
   NFRAC = "." digit+;
   NEXP  = [eE] [+\-]? digit+;
 }
 
 // STRING payload -> quotes, literal runs, and one escape atom per escape. The
 // catch-all SCHARS would have collided with the parser's "[" / "true" / ... if
 // parser literals were shared across lexers — they are not.
 %lex strescape {
   SQUOTE = "\"";
   SESC   = "\\" ( ["\\/bfnrt] | "u" [0-9A-Fa-f] [0-9A-Fa-f] [0-9A-Fa-f] [0-9A-Fa-f] );
   SCHARS = [^"\\]+;
 }
 
 %token TRUE  = "true";
 %token FALSE = "false";
 %token NULL  = "null";
 
 value   = object | array | STRING | NUMBER | "true" | "false" | "null";
 
 object  = "{" members? "}";
 members = member member_tail*;
 member_tail = "," member;
 member  = STRING ":" value;
 
 array   = "[" elements? "]";
 elements = value element_tail*;
 element_tail = "," value;