TinyRegex

Small and portable Regular Expression (regex) library written in BeefLang, based on https://github.com/kokke/tiny-regex-c.

Supports a subset of the syntax and semantics of the Python standard library implementation (the re module).

Notable features and omissions

• Small code: ~500 SLOC.
• No use of dynamic memory allocation (i.e. no calls to new / delete).
• To avoid call-stack exhaustion, iterative searching is preferred over recursive by default.
• All groups are non-capturing groups, there's no support for capturing groups or named capture: (^P<name>group) etc.
  • Groups can be disabled altogether with the TR_NO_GROUPS pre-processor flag.
• Greedy quantifiers can't be used inside of groups.
• Thorough testing: exrex is used to randomly generate test-cases from regex patterns, which are fed into the regex code for verification.

API

This is the public API:

/// Indicates whether the regular expression finds a match in the input string.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match.
public static bool IsMatch(StringView regex, StringView text);

/// Searches an input string for a substring that matches a regular expression pattern.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match.
public static Result<Match, MatchError> Match(StringView regex, StringView text);

/// Lazily enumerates over all matches of a regular expression pattern.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match.
public static MatchEnumerator Matches(StringView regex, StringView text);

/// Replaces the first string that matches a regular expression pattern with a specified replacement string.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match and which will be modified.
/// @param replace The replacement string.
public static void Replace(StringView regex, String text, StringView replace);

/// Replaces the first string that matches a regular expression pattern using a custom function.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match and which will be modified.
/// @param replaceFunc A custom function that modifies the match.
public static void Replace<TFunc>(StringView regex, String text, TFunc replaceFunc)
  where TFunc : delegate void(String match);

/// Replaces strings that match a regular expression pattern with a specified replacement string.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match and which will be modified.
/// @param replace The replacement string.
public static void ReplaceAll(StringView regex, String text, StringView replace);

/// Replaces strings that match a regular expression pattern using a custom function.
/// @param regex The regular expression pattern to match.
/// @param text The string to search for a match and which will be modified.
/// @param replaceFunc A custom function that modifies each match.
public static void ReplaceAll<TFunc>(StringView regex, String text, TFunc replaceFunc)
  where TFunc : delegate void(String match);

Supported regex-operators

The following features / regex-operators are supported by this library.

• . Dot, matches any character
• ^ Start anchor, matches beginning of string
• $ End anchor, matches end of string
• * Asterisk, match zero or more (greedy)
• + Plus, match one or more (greedy)
• ? Question, match zero or one (greedy)
• {m,n} Quantifier, match from m to n (greedy if m != n)
• [abc] Character class, match if one of {'a', 'b', 'c'}
• [^abc] Inverted class, match if NOT one of {'a', 'b', 'c'}
• [a-zA-Z] Character ranges, the character set of the ranges { a-z | A-Z }
• (expr) Groups, they are non-capturing by default.
• \s Whitespace, \t \f \r \n \v and spaces
• \S Non-whitespace
• \w Alphanumeric, [a-zA-Z0-9_]
• \W Non-alphanumeric
• \d Digits, [0-9]
• \D Non-digits

Examples

Example of usage:

if (Regex.Match(@"[Hh]ello [Ww]orld\s*[!]?", "ahem.. 'hello world !' ..") case .Ok(let match))
{
  Console.WriteLine($"Matched '{match.Value}' at index {match.Index}, {match.Length} chars long.");
  // outputs: Matched 'hello world !' at index 8, 13 chars long.
}

String text = scope .("24h 0x043k 0x4384");
Regex.ReplaceAll("0x([0-9]{2}){1,2}", text,
  (match) => {
    int num = int.Parse(match);
    match.Clear();
    (++num).ToString(match);
  });
Console.WriteLine(text);
// outputs: 24h 53k 17285

For more usage examples I encourage you to look at the code in the Tests project.