SeparatedRepeat

The SeparatedRepeat rule in RCParsing matches a child rule or token multiple times, interleaved with a separator rule or token. It’s ideal for parsing lists with delimiters, such as comma-separated values.

Overview

A SeparatedRepeat rule allows you to specify a child rule to repeat, a separator rule, and options for minimum/maximum repetitions, trailing separators, and whether to include separators in the AST.

Example

Here’s an example of parsing a comma-separated list of identifiers:

var builder = new ParserBuilder();

builder.CreateRule("identifier_list")
    .OneOrMoreSeparated(
        b => b.Identifier(),
        s => s.Literal(",")
    );

var parser = builder.Build();
var result = parser.ParseRule("identifier_list", "a,b,c"); // Matches "a", "b", "c"

With trailing separator allowed:

builder.CreateRule("identifier_list")
    .OneOrMoreSeparated(
        b => b.Identifier(),
        s => s.Literal(","),
        allowTrailingSeparator: true
    );

var parser = builder.Build();
var result = parser.ParseRule("identifier_list", "a,b,c,"); // Matches with trailing comma

Use Cases

• Lists: Parse comma-separated arguments or array elements.
• Expressions: Handle operators in expressions, e.g., a + b + c.
• Configuration Files: Parse key-value pairs separated by delimiters.

Transformation

The SeparatedRepeat rule produces an array of the repeated children’s values, optionally including separators if includeSeparatorsInResult is true:

builder.CreateRule("identifier_list")
    .OneOrMoreSeparated(
        b => b.Identifier(),
        s => s.Literal(",")
    )
    .Transform(v => v.Children.Select(c => c.Text).ToArray());

var parser = builder.Build();
var result = parser.ParseRule("identifier_list", "a,b,c");
var identifiers = result.Value as string[]; // ["a", "b", "c"]

builder.CreateRule("plus_expression")
    .OneOrMoreSeparated(
        b => b.Number<int>(),
        s => s.LiteralChoice("+"),
        includeSeparatorsInResult: true
    )
    .TransformFoldLeft<int, string, int>((l, o, r) => o == "+" ? l + r : l - r);

var parser = builder.Build();
var result = parser.ParseRule("plus_expression", "1+2+3");
var value = result.Value as int; // 6

Notes

• Trailing Separators: Set allowTrailingSeparator: true to allow lists like a,b,c,.
• Separator Inclusion: Use includeSeparatorsInResult: true to include separators in the Children array.
• Variants: ZeroOrMoreSeparated and OneOrMoreSeparated simplify common cases.

Related Tutorials

• Repeat Rule
• Sequence Rule
• Choice Rule