41 lines
859 B
Plaintext
41 lines
859 B
Plaintext
|
/*
|
||
|
|
* Simple Arithmetics Grammar
|
||
|
|
* ==========================
|
||
|
|
*
|
||
|
|
* Accepts expressions like "2 * (3 + 4)" and computes their value.
|
||
|
|
*/
|
||
|
|
|
||
|
|
Expression
|
||
|
|
= head:Term tail:(_ ("+" / "-") _ Term)* {
|
||
|
|
var result = head, i;
|
||
|
|
|
||
|
|
for (i = 0; i < tail.length; i++) {
|
||
|
|
if (tail[i][1] === "+") { result += tail[i][3]; }
|
||
|
|
if (tail[i][1] === "-") { result -= tail[i][3]; }
|
||
|
|
}
|
||
|
|
|
||
|
|
return result;
|
||
|
|
}
|
||
|
|
|
||
|
|
Term
|
||
|
|
= head:Factor tail:(_ ("*" / "/") _ Factor)* {
|
||
|
|
var result = head, i;
|
||
|
|
|
||
|
|
for (i = 0; i < tail.length; i++) {
|
||
|
|
if (tail[i][1] === "*") { result *= tail[i][3]; }
|
||
|
|
if (tail[i][1] === "/") { result /= tail[i][3]; }
|
||
|
|
}
|
||
|
|
|
||
|
|
return result;
|
||
|
|
}
|
||
|
|
|
||
|
|
Factor
|
||
|
|
= "(" _ expr:Expression _ ")" { return expr; }
|
||
|
|
/ Integer
|
||
|
|
|
||
|
|
Integer "integer"
|
||
|
|
= [0-9]+ { return parseInt(text(), 10); }
|
||
|
|
|
||
|
|
_ "whitespace"
|
||
|
|
= [ \t\n\r]*
|