Return

The Return token in RCParsing matches a child token and returns a fixed value, ignoring the child’s intermediate value. It’s useful for assigning constant values to specific matches.

Overview

The Return token wraps a single child token and returns a predefined value when the child matches, while not calculating the child's value. This is ideal for mapping specific tokens to fixed values, such as booleans or enums.

Example

Here’s an example of returning a boolean for a literal:

var builder = new ParserBuilder();

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

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

Use Cases

• Constant Values: Map keywords to booleans or enums.
• Simplified Parsing: Assign fixed values to specific tokens.
• Semantic Tokens: Represent specific tokens with constant meanings.

Intermediate Values

The Return token produces the fixed value specified, while instructs the child to not calculate intermediate value:

builder.CreateToken("number")
    .Return(b => b.Number<int>(), "yes, this is number");

var parser = builder.Build();
var result = parser.MatchToken("number", "123");
var value = result.GetIntermediateValue<string>(); // "yes, this is number"

Notes

• Fixed Value: The returned value is constant and ignores the child’s value.
• Single Child: Only one child token can be specified.
• No Rules: Tokens cannot reference rules, only other tokens.

Related Tutorials

• Map Token
• CaptureText Token
• Sequence Token