public StepResult(int cost, Func <Result <T> > nextResultFuture, SyntaxError err = null)
{
Cost = cost;
m_nextResultFuture = nextResultFuture;
m_error = err;
MyErrors = Enumerable.Empty <SyntaxError>();
}
public override Parse <TFuture> BuildParse <TFuture>(Future <string, TFuture> future)
{
Parse <TFuture> parse = null;
parse = scanner =>
{
// 保存读取当前单词之前的位置
ForkableScanner prevScanner = scanner.Fork();
Lexeme l = scanner.Read();
if (l.TokenIndex == m_token.Index)
{
return(new StepResult <TFuture>(0, () => future(l.Value.Content)(scanner)));
}
Lexeme recovery = l.GetErrorCorrectionLexeme(m_token.Index, m_token.Description);
SyntaxError insertionErr = Grammar.RecoverByInsertion(recovery);
if (l.IsEndOfStream)
{
// 已经到了输入的末尾
// 插入预期的Token进行恢复
return(new StepResult <TFuture>(1,
() => future(recovery.Value.Content)(prevScanner), insertionErr));
}
else
{
// 同时尝试插入预期的Token，以及删除当前字符
// 在未来的解析中选取更好的路线
return(Grammar.Best(
new StepResult <TFuture>(1, () => future(recovery.Value.Content)(prevScanner), insertionErr),
new StepResult <TFuture>(1, () => parse(scanner), Grammar.RecoverByDeletion(l))));
}
};
return(parse);
}