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Jan Lindemann
a3a8313ce8
First time parsing doesn't error out with a syntax error. No usable AST is produced, strings are not returned from lexer, and AST lists aren't lists, really. TEXT:="Hello world!"; had to be excluded from the example, because I don't get how this could be parsed with the given syntax. There's a special sequence "all visible characters", but any lexer regex I could think of will also match the types defining "alphabetic character" and return the respective tokens (e.g. T_A) or vice-versa, depending on the order in the lexer input file. I suppose, the only sensible way to handle this, is to define "all visible characters" by defining the tokens for the missing characters, and then use them along T_A ... T_Z or their derived types. Signed-off-by: Jan Lindemann <jan@janware.com>
16 lines
859 B
EBNF
16 lines
859 B
EBNF
(* a simple program syntax in EBNF − Wikipedia *)
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program = 'PROGRAM', white space, identifier, white space,
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'BEGIN', white space,
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{ assignment, ";", white space },
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'END.', [ white space ];
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identifier = alphabetic character, { alphabetic character | digit } ;
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number = [ "-" ], digit, { digit } ;
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string = '"' , { all characters }, '"' ;
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assignment = identifier , ":=" , ( number | identifier | string ) ;
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alphabetic character = "A" | "B" | "C" | "D" | "E" | "F" | "G"
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| "H" | "I" | "J" | "K" | "L" | "M" | "N"
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| "O" | "P" | "Q" | "R" | "S" | "T" | "U"
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| "V" | "W" | "X" | "Y" | "Z" ;
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digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
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white space = ? white space characters ? ;
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all characters = ? all visible characters ? ;
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