From 027fc4a5249b64b3cb44532ffd7cb34d46baac7d Mon Sep 17 00:00:00 2001
From: Victor <melnikukr@mail.ru>
Date: Thu, 16 Apr 2015 14:40:37 +0300
Subject: [PATCH] =?UTF-8?q?=D0=9F=D0=BE=D0=B4=D0=B4=D0=B5=D1=80=D0=B6?=
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 =?UTF-8?q?=20=D1=81=D0=BB=D0=BE=D0=B6=D0=B5=D0=BD=D0=B8=D1=8F=20=D0=B8=20?=
 =?UTF-8?q?=D0=B2=D1=8B=D1=87=D0=B8=D1=82=D0=B0=D0=BD=D0=B8=D1=8F?=
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---
 src/com/annimon/everlastingsummer/Parser.java | 21 +++++++++++-
 .../ast/BinaryExpression.java                 | 32 +++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 src/com/annimon/everlastingsummer/ast/BinaryExpression.java

diff --git a/src/com/annimon/everlastingsummer/Parser.java b/src/com/annimon/everlastingsummer/Parser.java
index 5eb4d4d..7b8b288 100644
--- a/src/com/annimon/everlastingsummer/Parser.java
+++ b/src/com/annimon/everlastingsummer/Parser.java
@@ -4,6 +4,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import com.annimon.everlastingsummer.ast.*;
+import com.annimon.everlastingsummer.ast.BinaryExpression.Operator;
 import android.text.TextUtils;
 
 /**
@@ -411,7 +412,25 @@ public final class Parser {
     }
     
     private Expression expression() {
-        return unary();
+        return additive();
+    }
+    
+    private Expression additive() {
+        Expression expression = unary();
+        
+        while (true) {
+            if (match(TokenType.PLUS)) {
+                expression = new BinaryExpression(Operator.ADD, expression, unary());
+                continue;
+            }
+            if (match(TokenType.MINUS)) {
+                expression = new BinaryExpression(Operator.SUBTRACT, expression, unary());
+                continue;
+            }
+            break;
+        }
+        
+        return expression;
     }
     
     private Expression unary() {
diff --git a/src/com/annimon/everlastingsummer/ast/BinaryExpression.java b/src/com/annimon/everlastingsummer/ast/BinaryExpression.java
new file mode 100644
index 0000000..a5c8e34
--- /dev/null
+++ b/src/com/annimon/everlastingsummer/ast/BinaryExpression.java
@@ -0,0 +1,32 @@
+package com.annimon.everlastingsummer.ast;
+
+/**
+ * @author aNNiMON
+ */
+public class BinaryExpression implements Expression {
+    
+    public static enum Operator {
+        ADD, SUBTRACT
+    }
+
+    public final Operator operator;
+    private final Expression left, right;
+
+    public BinaryExpression(Operator op, Expression left, Expression right) {
+        this.operator = op;
+        this.left = left;
+        this.right = right;
+    }
+
+    @Override
+    public double eval() {
+        final double leftVal = left.eval();
+        final double rightVal = right.eval();
+        switch (operator) {
+            case ADD: return leftVal + rightVal;
+            case SUBTRACT: return leftVal - rightVal;
+            default:
+                throw new RuntimeException("Неизвестный оператор " + operator.name());
+        }
+    }
+}