digit_nonzero = "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ; digit = "0" | digit_nonzero ; integer = "0" | ( ["-"] , digit_nonzero , { digit } ) ;
real = ["-"] , digit , { digit } , "." , digit , { digit } ;
boolean_literal = "true" | "false" ;
letter_lower = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" ; letter_upper = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" ; letter = letter_lower | letter_upper ; name_lower = letter_lower , { letter | digit | "-" | "_" } ; name_upper = letter_upper , { letter | digit | "-" | "_" } ;