Fail

The Fail token in RCParsing always fails without consuming input. It’s used to explicitly block a parsing path in a grammar.

Overview

The Fail token is a zero-width token that immediately fails, producing no intermediate value. It’s useful for enforcing constraints or preventing certain matches in Choice or other combinators.

Example

var builder = new ParserBuilder();

builder.CreateToken("no_match")
    .Fail();

var parser = builder.Build();
var result = parser.MatchToken("no_match", "anything"); // Fails

Use Cases

• Block Paths: Prevent specific branches in a Choice token.
• Constraints: Enforce parsing rules by failing invalid paths.
• Debugging: Test parser behavior by forcing failure.

Intermediate Values

The Fail token never succeeds, so it produces no intermediate value.

Notes

• Zero-Width: Does not consume any input.
• Always Fails: Useful for explicitly invalid patterns.

Related Tutorials

• Empty Token
• Choice Token
• Lookahead Token