Add collection for expressions

Additionly type field was added to all Expression classes
Refs: metarhia#5

lib/expressions.js

@@ -5,22 +5,28 @@ const OPERATORS = require('./operators.js');
 const BOOL = {
   t: true,
   nil: false,
+  true: true,
+  false: false,
 };
 
 class BooleanExpression {
+  type = 'boolean';
+
   constructor(value) {
     if (!(value in BOOL)) {
       throw new Error(`Unknown boolean value: ${value}`);
     }
-    this.value = value;
+    this.value = BOOL[value];
   }
 
   interpret() {
-    return BOOL[this.value];
+    return this.value;
   }
 }
 
 class NumberExpression {
+  type = 'number';
+
   constructor(value) {
     this.value = parseFloat(value);
   }
@@ -31,6 +37,8 @@ class NumberExpression {
 }
 
 class VariableExpression {
+  type = 'variable';
+
   constructor(name) {
     this.name = name;
   }
@@ -44,6 +52,8 @@ class VariableExpression {
 }
 
 class OperationExpression {
+  type = 'operation';
+
   constructor(operator, operands) {
     this.operator = operator;
     this.operands = operands;
@@ -59,10 +69,34 @@ class OperationExpression {
   }
 }
 
+const expressions = {
+  number: NumberExpression,
+  variable: VariableExpression,
+  boolean: BooleanExpression,
+  operation: OperationExpression,
+};
+
+const expressionType = {
+  number: 'number',
+  variable: 'variable',
+  operation: 'operation',
+  boolean: 'boolean',
+};
+
+const getExpressionType = (token) => {
+  if (Array.isArray(token)) return expressionType.operation;
+  if (!isNaN(token)) return expressionType.number;
+  if (token in BOOL) return expressionType.boolean;
+  return expressionType.variable;
+};
+
 module.exports = {
   NumberExpression,
   VariableExpression,
   OperationExpression,
   BooleanExpression,
   BOOL,
+  expressions,
+  expressionType,
+  getExpressionType,
 };

lib/parser.js

@@ -1,11 +1,9 @@
 'use strict';
 
 const {
-  NumberExpression,
-  VariableExpression,
-  OperationExpression,
-  BooleanExpression,
-  BOOL,
+  expressions,
+  expressionType,
+  getExpressionType,
 } = require('./expressions.js');
 
 const tokenize = (source) => {
@@ -34,22 +32,16 @@ const tokenize = (source) => {
   return stack[0];
 };
 
-const expressionFactory = (token) => {
-  if (!isNaN(token)) return new NumberExpression(token);
-  if (token in BOOL) {
-    return new BooleanExpression(token);
-  }
-  return new VariableExpression(token);
-};
-
 const parse = (tokens) => {
-  if (!Array.isArray(tokens)) {
-    return expressionFactory(tokens);
+  const type = getExpressionType(tokens);
+  const Expression = expressions[type];
+  if (type !== expressionType.operation) {
+    return new Expression(tokens);
   }
   const operator = tokens[0];
   const operands = tokens.slice(1);
   const operandExpressions = operands.map((x) => parse(x));
-  return new OperationExpression(operator, operandExpressions);
+  return new Expression(operator, operandExpressions);
 };
 
 const evaluate = (input, context = {}) => {