Implement the while statement

fixes #8269

doc/15-language-reference.md

@@ -668,6 +668,20 @@ This example prints the log message "Taking the 'true' branch" and the `a` varia
 
 The value of an if/else construct is null if the condition evaluates to false and no else branch is given.
 
+## <a id="while-loops"></a> While Loops
+
+The `while` statement checks a condition and executes the loop body when the condition evaluates to `true`.
+This is repeated until the condition is no longer true.
+
+Example:
+
+    var num = 5
+
+    while (num > 5) {
+        log("Test")
+        num -= 1
+    }
+
 ## <a id="for-loops"></a> For Loops
 
 The `for` statement can be used to iterate over arrays and dictionaries.

lib/config/config_lexer.ll

@@ -204,6 +204,7 @@ return				return T_RETURN;
 for				return T_FOR;
 if				return T_IF;
 else				return T_ELSE;
+while				return T_WHILE;
 =\>				return T_FOLLOWS;
 \<\<				return T_SHIFT_LEFT;
 \>\>				return T_SHIFT_RIGHT;

lib/config/config_parser.yy

@@ -174,6 +174,7 @@ static void MakeRBinaryOp(Expression** result, Expression *left, Expression *rig
 %token T_FOR "for (T_FOR)"
 %token T_IF "if (T_IF)"
 %token T_ELSE "else (T_ELSE)"
+%token T_WHILE "while (T_WHILE)"
 %token T_FOLLOWS "=> (T_FOLLOWS)"
 
 %type <text> identifier
@@ -644,6 +645,13 @@ lterm: type
 		BindToScope(expr, ScopeLocal);
 		$$ = new SetExpression(expr, $3, $4, @$);
 	}
+	| T_WHILE '(' rterm ')' rterm_scope
+	{
+		DictExpression *aloop = dynamic_cast<DictExpression *>($5);
+		aloop->MakeInline();
+
+		$$ = new WhileExpression($3, aloop, @$);
+	}
 	| rterm_side_effect
 	;
 	

lib/config/expression.cpp

@@ -400,6 +400,14 @@ Value ConditionalExpression::DoEvaluate(ScriptFrame& frame, DebugHint *dhint) co
 	return Empty;
 }
 
+Value WhileExpression::DoEvaluate(ScriptFrame& frame, DebugHint *dhint) const
+{
+	while (m_Condition->Evaluate(frame, dhint).ToBool())
+		m_LoopBody->Evaluate(frame, dhint);
+
+	return Empty;
+}
+
 Value ReturnExpression::DoEvaluate(ScriptFrame& frame, DebugHint *dhint) const
 {
 	BOOST_THROW_EXCEPTION(InterruptExecutionError(m_Operand->Evaluate(frame)));

lib/config/expression.hpp

@@ -632,6 +632,28 @@ private:
 	Expression *m_FalseBranch;
 };
 
+class I2_CONFIG_API WhileExpression : public DebuggableExpression
+{
+public:
+	WhileExpression(Expression *condition, Expression *loop_body, const DebugInfo& debugInfo = DebugInfo())
+		: DebuggableExpression(debugInfo), m_Condition(condition), m_LoopBody(loop_body)
+	{ }
+
+	~WhileExpression(void)
+	{
+		delete m_Condition;
+		delete m_LoopBody;
+	}
+
+protected:
+	virtual Value DoEvaluate(ScriptFrame& frame, DebugHint *dhint) const;
+
+private:
+	Expression *m_Condition;
+	Expression *m_LoopBody;
+};
+
+
 class I2_CONFIG_API ReturnExpression : public UnaryExpression
 {
 public: