Repeat

The Repeat rule in RCParsing matches a child rule or token a specified number of times within a given range. It fails if the child does not match at least the minimum number of times. This rule is useful for parsing lists or repeated patterns.

Overview

A Repeat rule allows you to specify a minimum and optional maximum number of times a child rule or token should match. Variants like ZeroOrMore and OneOrMore simplify common cases.

Example

Here’s an example of a Repeat rule for parsing a list of identifiers:

var builder = new ParserBuilder();

builder.Settings.SkipWhitespaces();

builder.CreateRule("identifiers")
    .Repeat(b => b.Identifier(), min: 1, max: 3); // Matches 1 to 3 identifiers

var parser = builder.Build();
var result1 = parser.ParseRule("identifiers", "a b c"); // Matches "a", "b", "c"
var result2 = parser.ParseRule("identifiers", "d e f g"); // Matches "d", "e", "f"
var result3 = parser.ParseRule("identifiers", "d e 0 g"); // Matches "d", "e"

Using OneOrMore for a similar effect:

builder.CreateRule("identifiers")
    .OneOrMore(b => b.Identifier()); // Matches 1 or more identifiers

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

Use Cases

• Lists: Parse lists of items, such as variables or arguments.
• Repeated Patterns: Match repeated keywords or tokens, e.g., multiple else clauses.
• Flexible Counts: Allow a variable number of matches within a range.

Transformation

The Repeat rule produces an array of the children’s values:

builder.CreateRule("identifiers")
    .OneOrMore(b => b.Identifier())
    .Transform(v => v.Children.Select(c => c.Text).ToArray());

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

Notes

• Range Specification: Use min and max to control the number of matches. Omit max for unbounded repeats.
• Variants: ZeroOrMore (0 or more) and OneOrMore (1 or more) are shortcuts for common cases.
• Failure: Fails if fewer than min matches are found.

Related Tutorials

• SeparatedRepeat Rule
• Optional Rule
• Sequence Rule