Keyword

The Keyword token in RCParsing matches a specific string but fails if it’s followed by certain characters, such as letters or digits. It’s used for parsing keywords that must not be part of a larger word.

Overview

The Keyword token ensures that the matched string is not followed by characters that would make it part of a larger identifier. It uses predicates to define forbidden trailing characters and produces the construction-specified string as its intermediate value.

Example

Here’s an example of parsing a keyword:

var builder = new ParserBuilder();

builder.CreateToken("var")
    .Keyword("var");

var parser = builder.Build();
var result1 = parser.MatchToken("var", "var"); // Succeeds
var result2 = parser.MatchToken("var", "var "); // Succeeds
var result3 = parser.MatchToken("var", "var;"); // Succeeds
var result4 = parser.MatchToken("var", "variable"); // Fails

With a custom predicate:

builder.CreateToken("var")
    .Keyword("var", c => char.IsDigit(c)); // Fails if followed by a digit

var parser = builder.Build();
var result = parser.MatchToken("var", "var1"); // Fails

Use Cases

• Language Keywords: Match var, if, or while as distinct tokens.
• Boundary Enforcement: Ensure keywords are not part of larger words.
• Custom Constraints: Use predicates to define specific trailing character rules.

Intermediate Values

The Keyword token produces the original string that was specified in construction as its intermediate value:

builder.CreateToken("if")
    .KeywordIgnoreCase("iF");

var parser = builder.Build();
var result = parser.MatchToken("if", "If");
var value = result.GetIntermediateValue<string>(); // "iF"

Notes

• Default Predicates: Uses ASCII or Unicode identifier predicates by default.
• Case Sensitivity: Supports StringComparison for case-insensitive matching.

Related Tutorials

• KeywordChoice Token
• Literal Token
• Identifier Token