From 9794c2f01c5953225f12454a317ace1d14df5e05 Mon Sep 17 00:00:00 2001
From: otya128 <otya128@users.noreply.github.com>
Date: Sun, 7 Jun 2015 21:03:55 +0900
Subject: [PATCH] =?UTF-8?q?RETURN=20without=20GOSUB=E3=81=99=E3=82=8B?=
 =?UTF-8?q?=E3=82=88=E3=81=86=E3=81=AB=E3=81=97=E3=81=9F?=
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---
 SMILEBASIC/VM.d    | 12 +++++++++++-
 SMILEBASIC/error.d |  9 ++++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/SMILEBASIC/VM.d b/SMILEBASIC/VM.d
index 9ce432f..f53f9e2 100644
--- a/SMILEBASIC/VM.d
+++ b/SMILEBASIC/VM.d
@@ -14,6 +14,7 @@ class VM
     Value[] stack;
     Value[] global;
     int[wstring] globalTable;
+    int bp;
     ValueType getType(wstring name)
     {
         wchar s = name[name.length - 1];
@@ -42,6 +43,7 @@ class VM
     }
     void run()
     {
+        bp = 0;//globalを実行なのでbaseは0(グローバル変数をスタックに取るようにしない限り)
         for(pc = 0; pc < this.code.length; pc++)
         {
             code[pc].execute(this);
@@ -55,9 +57,13 @@ class VM
     {
         stack[stacki++] = value;
     }
+    bool canPop()
+    {
+        return stacki > bp;
+    }
     void pop(out Value value)
     {
-        if(stacki <= 0)
+        if(stacki <= bp)
         {
             writeln("Stack underflow");
             readln();
@@ -462,6 +468,10 @@ class ReturnSubroutine : Code
     override void execute(VM vm)
     {
         Value pc;
+        if(!vm.canPop())
+        {
+            throw new ReturnWithoutGosub();
+        }
         vm.pop(pc);
         if(pc.type != ValueType.Integer || pc.integerValue < 0 || pc.integerValue >= vm.code.length)
         {
diff --git a/SMILEBASIC/error.d b/SMILEBASIC/error.d
index f3fadd2..f07023f 100644
--- a/SMILEBASIC/error.d
+++ b/SMILEBASIC/error.d
@@ -35,4 +35,11 @@ class DuplicateVariable : SmileBasicError
         super("Duplicate variable");
     }
 }
-
+class ReturnWithoutGosub : SmileBasicError
+{
+    this()
+    {
+        this.errnum = 30;
+        super("RETURN without GOSUB");
+    }
+}