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Regex

Why

Provides regular expression matching via the system POSIX regex.h. Uses extended regex syntax (REG_EXTENDED). No extra libraries needed beyond what the OS provides.

Types

  • Regex (ADDRESS) -- Opaque compiled pattern handle.
  • Match -- Record with start: CARDINAL (byte offset) and len: CARDINAL (match length).
  • Status -- Ok, NoMatch, BadPattern, Error.

Constants

  • MaxMatches = 32 -- Maximum number of matches returned by FindAll.
  • MaxErrorLen = 256 -- Maximum error message length.

Procedures

Lifecycle

  • PROCEDURE Compile(pattern: ARRAY OF CHAR; VAR re: Regex): Status Compile a regex pattern. Returns BadPattern if the pattern is invalid.

  • PROCEDURE Free(VAR re: Regex) Free a compiled pattern.

Matching

  • PROCEDURE Test(re: Regex; text: ARRAY OF CHAR): BOOLEAN Test whether text matches the pattern. Returns TRUE/FALSE.

  • PROCEDURE Find(re: Regex; text: ARRAY OF CHAR; VAR m: Match): Status Find the first match in text. Fills m with the match position.

  • PROCEDURE FindAll(re: Regex; text: ARRAY OF CHAR; VAR matches: ARRAY OF Match; maxMatches: CARDINAL; VAR count: CARDINAL): Status Find all non-overlapping matches. Returns up to maxMatches results.

Error Handling

  • PROCEDURE GetError(VAR buf: ARRAY OF CHAR) Copy the last error message into buf.

Example

MODULE RegexDemo;

FROM InOut IMPORT WriteString, WriteLn, WriteCard;
FROM Regex IMPORT Regex, Match, Status, Compile, Find, Free, Ok;

VAR
  re: Regex;
  m: Match;
  s: Status;

BEGIN
  s := Compile("[0-9]+", re);
  IF s = Ok THEN
    s := Find(re, "version 42 released", m);
    IF s = Ok THEN
      WriteString("found at offset ");
      WriteCard(m.start, 0);
      WriteString(", length ");
      WriteCard(m.len, 0);
      WriteLn
    END;
    Free(re)
  END
END RegexDemo.