arithmetics.pegjs
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/*
* Simple Arithmetics Grammar
* ==========================
*
* Accepts expressions like "2 * (3 + 4)" and computes their value.
*/
{
function combine(first, rest, combiners) {
var result = first, i;
for (i = 0; i < rest.length; i++) {
result = combiners[rest[i][1]](result, rest[i][3]);
}
return result;
}
}
Expression
= first:Term rest:(_ ("+" / "-") _ Term)* {
return combine(first, rest, {
"+": function(left, right) { return left + right; },
"-": function(left, right) { return left - right; }
});
}
Term
= first:Factor rest:(_ ("*" / "/") _ Factor)* {
return combine(first, rest, {
"*": function(left, right) { return left * right; },
"/": function(left, right) { return left / right; }
});
}
Factor
= "(" _ expr:Expression _ ")" { return expr; }
/ Integer
Integer "integer"
= [0-9]+ { return parseInt(text(), 10); }
_ "whitespace"
= [ \t\n\r]*