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pegjs/examples/arithmetics.pegjs

31 lines
814 B
JavaScript

// Simple Arithmetics Grammar
// ==========================
//
// Accepts expressions like "2 * (3 + 4)" and computes their value.
Expression
= head:Term tail:(_ ("+" / "-") _ Term)* {
return tail.reduce(function(result, element) {
if (element[1] === "+") { return result + element[3]; }
if (element[1] === "-") { return result - element[3]; }
}, head);
}
Term
= head:Factor tail:(_ ("*" / "/") _ Factor)* {
return tail.reduce(function(result, element) {
if (element[1] === "*") { return result * element[3]; }
if (element[1] === "/") { return result / element[3]; }
}, head);
}
Factor
= "(" _ expr:Expression _ ")" { return expr; }
/ Integer
Integer "integer"
= _ [0-9]+ { return parseInt(text(), 10); }
_ "whitespace"
= [ \t\n\r]*