The Practice of Programming

Question

At 1998, Brian Kernighan, while working on the book "The Practice of Programming", wanted to demonstrate realisation of regular expression engine. But struggled to find small engine, that cod could fit in the book.

So Brian Kernighan asked Rob Pike to write one for him, and Rob did it gracefully. Here is original source:

    /* match: search for regexp anywhere in text */
    int match(char *regexp, char *text)
    {
        if (regexp[0] == '^')
            return matchhere(regexp+1, text);
        do {    /* must look even if string is empty */
            if (matchhere(regexp, text))
                return 1;
        } while (*text++ != '\0');
        return 0;
    }

    /* matchhere: search for regexp at beginning of text */
    int matchhere(char *regexp, char *text)
    {
        if (regexp[0] == '\0')
            return 1;
        if (regexp[1] == '*')
            return matchstar(regexp[0], regexp+2, text);
        if (regexp[0] == '$' && regexp[1] == '\0')
            return *text == '\0';
        if (*text!='\0' && (regexp[0]=='.' || regexp[0]==*text))
            return matchhere(regexp+1, text+1);
        return 0;
    }

    /* matchstar: search for c*regexp at beginning of text */
    int matchstar(int c, char *regexp, char *text)
    {
        do {    /* a * matches zero or more instances */
            if (matchhere(regexp, text))
                return 1;
        } while (*text != '\0' && (*text++ == c || c == '.'));
        return 0;
    }

Rules

• Write regex engine that supports the same operations, as Rob's:
  • Any char (as symbol)
  • . to match any char
  • ^ to match start of the string
  • $ to match end of the string
  • * to match any count of char from zero
• Auxiliary code do not count (to accept input, for example)
• Make the shortest solution and beat Rob Pike!

Input

Two strings: one for regex, one for match.

Output

• True (in your language), if regex matches string
• False (in your language), if regex do not match string

Answer 1

Perl 6, 39 bytes

->\a{&{?/<{a}>/}}o{S:g/<-[.*$^]>/'$/'/}

Try it online!

Simply evaluates the input as a regex, adding quotes to avoid any special characters Perl 6 uses. This takes input curried, as f(regex)(string), though it could be a lot shorter if I can just return a regex object.