JSON representation of arithmetic expression

__tests__/expression_evaluator.test.js

@@ -2,22 +2,22 @@
 const {evaluate} = require("../expression/expression_evaluator");
 const {tAdd, tSub, tMul, tDiv, tInt} = require('../expression/expression_ast');
 
-test('1 + 1 == 2', () => {
+test('1 + 1 ==> 2', () => {
     const e = tAdd(tInt(1), tInt(1));
     expect(evaluate(e)).toBe(2);
 });
 
-test('1 + 2 + 3 == 7', () => {
-    const e = tAdd(tInt(1), tInt(1));
-    expect(evaluate(e)).toBe(2);
+test('1 + 2 + 3 ==> 6', () => {
+    const e = tAdd(tInt(1), tAdd(tInt(2), tInt(3)));
+    expect(evaluate(e)).toBe(6);
 });
 
-test('1 - 1 == 0', () => {
+test('1 - 1 ==> 0', () => {
     const e = tSub(tInt(1), tInt(1));
     expect(evaluate(e)).toBe(0);
 });
 
-test('1 - 2 == 0', () => {
+test('1 - 2 ==> -1', () => {
     const e = tSub(tInt(1), tInt(2));
     expect(evaluate(e)).toBe(-1);
 });

__tests__/expression_json_evaluator.test.js

@@ -0,0 +1,62 @@
+"use strict";
+const {evaluateJson} = require("../expression/expression_json_evaluator");
+
+test('1 + 1 ==> 2', () => {
+    const e =  `["+", 1, 1]`;
+    expect(evaluateJson(e)).toBe(2);
+});
+
+test('1 + 2 + 3 ==> 7', () => {
+    const e = `["+", 1, ["+", 2, 3]]`;
+    expect(evaluateJson(e)).toBe(6);
+});
+
+test('1 - 1 ==> 0', () => {
+    const e = `["-", 1, 1]`;
+    expect(evaluateJson(e)).toBe(0);
+});
+
+test('1 - 2 ==> -1', () => {
+    const e = `["-", 1, 2]`;
+    expect(evaluateJson(e)).toBe(-1);
+});
+
+test('1 * 1 ==> 1', () => {
+    const e = `["*", 1, 1]`;
+    expect(evaluateJson(e)).toBe(1);
+});
+
+test('1 * 0 ==> 0', () => {
+    const e = `["*", 1, 0]`;
+    expect(evaluateJson(e)).toBe(0);
+});
+
+test('2 * 2 ==> 4', () => {
+    const e = `["*", 2, 2]`;
+    expect(evaluateJson(e)).toBe(4);
+});
+
+test('0 / 1 ==> 0', () => {
+    const e = `["/", 0, 1]`;
+    expect(evaluateJson(e)).toBe(0);
+});
+
+test('2 / 1 ==> 2', () => {
+    const e = `["/", 2, 1]`;
+    expect(evaluateJson(e)).toBe(2);
+});
+
+test('6 / 2 ==> 3', () => {
+    const e = `["/", 6, 2]`;
+    expect(evaluateJson(e)).toBe(3);
+});
+
+test('(1 + (2 * 3) - 1) / 2 == 3', () => {
+    const e =
+        `["/", 
+            ["-", 
+                ["+", 1, ["*", 2, 3]], 
+                1], 
+            2]`
+    expect(evaluateJson(e)).toBe(3);
+});

expression/expression_json_evaluator.js

@@ -0,0 +1,20 @@
+const {BinExpr, Int} = require('./expression_ast');
+const {evaluate} = require('./expression_evaluator');
+function translateToAst(json) {
+    if(typeof(json) === 'number') {
+        return new Int(json);
+    } else if(Array.isArray(json)) {
+        const op = json[0];
+        const lhs = translateToAst(json[1]);
+        const rhs = translateToAst(json[2]);
+        return new BinExpr(op, lhs, rhs);
+    } else {
+        throw new Error("Not implemented for: " + JSON.stringify(json));
+    }
+}
+function evaluateJson(jsonString) {
+    const e = JSON.parse(jsonString);
+    const ast = translateToAst(e);
+    return evaluate(ast);
+}
+module.exports = {evaluateJson};