pegjs/examples/arithmetics.pegjs

/*
 * Classic example grammar, which recognizes simple arithmetic expressions like
 * "2*(3+4)". The parser generated from this grammar then computes their value.
 */

start             = additive

additive          = multiplicative "+" additive { return $1 + $3; }
                  / multiplicative

multiplicative    = primary "*" multiplicative { return $1 * $3; }
                  / primary

primary           = integer
                  / "(" additive ")" { return $2; }

integer "integer" = [0-9]+ { return parseInt($1.join(""), 10); }