private static EvalValue CalcWhile(IEnvironment env, AstWhile ast)
{
// 返回值为最后一条语句或表达式的值
var ret = new EvalValue();
while (true)
{
var cond = ast.condition.Eval(env);
if (cond.type == EvalValueType.INT && cond.intVal > 0)
{
// 当条件满足时执行代码块中的每一条子语句
foreach (var item in ast)
{
ret = item.Eval(env);
}
}
else if (cond.type == EvalValueType.STRING)
{
throw new RunTimeException("条件表达式不能为字符串", ast.condition);
}
else
{
break;
}
}
return(ret);
}
static AstNode RemoveUnreachableCode(AstWhile whileStatement)
{
if (TypeConverter.ToBoolean(whileStatement.Condition.ConstValue() ?? AstTrue.Instance))
{
return(whileStatement);
}
var declarations = GetDeclarations(whileStatement.Body);
return(declarations ?? Remove);
}
/// <summary>
/// 解析语句state
/// </summary>
/// <returns></returns>
private AstStatement DoStatement()
{
// state ::== <while><expr><do>{<expr>|<state>}<end>';'
// | <if><expr><do>{<expr>|<state>}<end>';'
// | <return><expr>';'
if (Is("while", TokenType.KEYWORD))
{
// while语句
Pass("while", TokenType.KEYWORD);
AstExpression condition = DoExpression();
Pass("do", TokenType.KEYWORD);
List <AstNode> list = DoBlock();
Pass("end", TokenType.KEYWORD);
Pass(";", TokenType.SEPERATOR);
var ret = new AstWhile(list, condition);
Utils.LogDebug("[P] while语句: {0}", ret.ToString());
return(ret);
}
if (Is("if", TokenType.KEYWORD))
{
// if语句
Pass("if", TokenType.KEYWORD);
AstExpression condition = DoExpression();
Pass("do", TokenType.KEYWORD);
List <AstNode> list = DoBlock();
List <AstNode> elseList = null;
if (Is("else", TokenType.KEYWORD))
{
// 有else块
Pass("else", TokenType.KEYWORD);
elseList = DoBlock();
}
Pass("end", TokenType.KEYWORD);
Pass(";", TokenType.SEPERATOR);
var ret = new AstIf(list, condition, elseList);
Utils.LogDebug("[P] if语句: {0}", ret.ToString());
return(ret);
}
if (Is("return", TokenType.KEYWORD))
{
// return语句
Pass("return", TokenType.KEYWORD);
AstExpression expr = DoExpression();
var ret = new AstReturn(new List <AstNode>(), expr);
Utils.LogDebug("[P] return语句: {0}", ret.ToString());
return(ret);
}
throw new ParseException(m_scanner.Peek(0), "未知语句");
}
private void CompileWhile(AstWhile node, Syt syt, StringBuilder sb)
{
var lblWhile = Id("WHILE");
var lblTrue = Id("WHILE_TRUE");
var lblEnd = Id("WHILE_END");
sb.AppendLine("label " + lblWhile);
CompileRecursive(node.exprCond, syt, sb);
sb.AppendLine("if-goto " + lblTrue);
sb.AppendLine("goto " + lblEnd);
sb.AppendLine("label " + lblTrue);
CompileRecursive(node.rgstm, syt, sb);
sb.AppendLine("goto " + lblWhile);
sb.AppendLine("label " + lblEnd);
}