Feature - Support plus binary expression for number and string

src/acorn-helpers/isType.ts

@@ -6,6 +6,7 @@ import {
   NumericLiteral,
   StringLiteral,
   Program,
+  BinaryExpression,
 } from './types';
 
 export function isProgram(node: Node): node is Program {
@@ -27,3 +28,7 @@ export function isNumericLiteral(node: Node): node is NumericLiteral {
 export function isStringLiteral(node: Node): node is StringLiteral {
   return isLiteral(node) && typeof node.value === 'string';
 }
+
+export function isBinaryExpression(node: Node): node is BinaryExpression {
+  return node.type === TypeStrings.BinaryExpression;
+}

src/acorn-helpers/types.ts

@@ -6,6 +6,7 @@ export enum TypeStrings {
   Program = 'Program',
   ExpressionStatement = 'ExpressionStatement',
   Literal = 'Literal',
+  BinaryExpression = 'BinaryExpression',
 }
 
 export interface Program extends Node {
@@ -18,7 +19,8 @@ export interface ExpressionStatement extends Node {
   expression: Expression;
 }
 
-export type Expression = Literal | Node;
+// TODO: Add more possible type of expressions here and remove generic node
+export type Expression = Literal | BinaryExpression | Node;
 
 export interface Literal extends Node {
   type: TypeStrings.Literal;
@@ -34,3 +36,11 @@ export interface StringLiteral extends Node {
   type: TypeStrings.Literal;
   value: string;
 }
+
+export interface BinaryExpression extends Node {
+  type: TypeStrings.BinaryExpression;
+  left: Literal;
+  right: Literal;
+  // TODO: Add actual possible operators here
+  operator: string;
+}

src/evaluate.ts

@@ -4,11 +4,13 @@ import {
   isNumericLiteral,
   isStringLiteral,
   isProgram,
+  isBinaryExpression,
 } from './acorn-helpers/isType';
 
 import {
   NormalCompletion,
   CompletionRecord,
+  v,
 } from './internal-types/CompletionRecord';
 
 import { NumberValue } from './language-types/NumberValue';
@@ -30,6 +32,22 @@ export function Evaluate(node: Node): CompletionRecord {
   } else if (isStringLiteral(node)) {
     // Handle StringLiteral
     return NormalCompletion(new StringValue(node.value));
+  } else if (isBinaryExpression(node)) {
+    if (node.operator === '+') {
+      // TODO - Forward completion record for abrupt completions
+      const leftVal = v(Evaluate(node.left));
+      const rightVal = v(Evaluate(node.right));
+      if (leftVal instanceof NumberValue && rightVal instanceof NumberValue) {
+        return NormalCompletion(
+          new NumberValue(leftVal.getValue() + rightVal.getValue())
+        );
+      }
+      if (leftVal instanceof StringValue && rightVal instanceof StringValue) {
+        return NormalCompletion(
+          new StringValue(leftVal.getValue() + rightVal.getValue())
+        );
+      }
+    }
   } else {
     // If not handled, throw error
     throwUnknownNode(node);

src/internal-types/CompletionRecord.ts

@@ -29,3 +29,13 @@ export class CompletionRecord implements TCompletionRecord {
 export function NormalCompletion(value?: TValue) {
   return new CompletionRecord('normal', value);
 }
+
+export function v(cr: CompletionRecord): LanguageType | undefined {
+  if (cr[TypeString] === 'normal') {
+    return cr[ValueString];
+  }
+  // TODO: Else, from call site, return same value
+  return undefined;
+}
+
+export class AbruptCompletion extends TypeError {}

src/language-types/NumberValue.ts

@@ -3,6 +3,7 @@ import { NumberString } from './typeNames';
 export interface TNumberValue {
   type: typeof NumberString;
   value: number;
+  getValue(): number;
 }
 
 export class NumberValue implements TNumberValue {
@@ -13,4 +14,8 @@ export class NumberValue implements TNumberValue {
     this.type = NumberString;
     this.value = value;
   }
+
+  getValue(): number {
+    return this.value;
+  }
 }

src/language-types/StringValue.ts

@@ -3,6 +3,7 @@ import { StringString } from './typeNames';
 export interface TStringValue {
   type: typeof StringString;
   value: string;
+  getValue(): string;
 }
 
 export class StringValue implements TStringValue {
@@ -13,4 +14,8 @@ export class StringValue implements TStringValue {
     this.type = StringString;
     this.value = value;
   }
+
+  getValue(): string {
+    return this.value;
+  }
 }