Empty

The Empty token in RCParsing matches zero characters at the current position and always succeeds. It’s a zero-width token used for placeholder or anchoring purposes in parsing.

Overview

The Empty token does not consume any input and succeeds immediately, producing no intermediate value by default. It’s useful for marking positions or enabling optional parsing without affecting the input.

Example

Here’s an example of using the Empty token as a placeholder:

var builder = new ParserBuilder();

builder.CreateToken("empty")
    .Empty();

var parser = builder.Build();
var result = parser.MatchToken("empty", "text"); // Succeeds at position 0

Use Cases

• Placeholder: Use in sequences where a token is optional but a position must be marked.
• Anchoring: Anchor rules or tokens without consuming input.
• Default Cases: Provide a no-op token in choice constructs.

Intermediate Values

The Empty token produces no intermediate value unless wrapped with a combinator:

builder.CreateToken("empty")
    .Return(b => b.Empty(), true);

var parser = builder.Build();
var result = parser.MatchToken("empty", "text");
var value = result.GetIntermediateValue<bool>(); // true

Notes

• Zero-Width: Does not consume any input.
• Always Succeeds: Never fails, making it safe for optional positions.

Related Tutorials

• Sequence Token
• Optional Token
• Return Token