@parser-generator/grammar-interpreter/lib/esm/__tests__/arithmetic/lr/ast.js

A Parser Generator that supports LL,SLR,LR1,LALR

import { Single } from "../lexer";
/*
E-> E+E | E-E | E*E | E/E | (E) |digit
*/
export class Expr {
    constructor(eles) {
        this.children = eles;
    }
    eval() {
        let first = this.children[0];
        if (this.children.length == 3) {
            //(E)
            if (first instanceof Single) {
                return this.children[1].eval();
            }
            //E op E
            else {
                let left = this.children[0];
                let op = this.children[1].value();
                let right = this.children[2];
                switch (op) {
                    case "+":
                        return left.eval() + right.eval();
                    case "-":
                        return left.eval() - right.eval();
                    case "*":
                        return left.eval() * right.eval();
                    case "/":
                        return left.eval() / right.eval();
                    default:
                        throw new Error(`Unknown token :${op}`);
                }
            }
        }
        //NUM
        else {
            return first.value();
        }
    }
}
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