An automaton-based regex implementation for [zig](http://ziglang.org/).

Note: This is still a work in progress and many things still need to be done.

 - [x] Capture group support
 - [ ] UTF-8 support
 - [ ] More tests (plus some automated tests/fuzzing)
 - [x] Add a PikeVM implementation
 - [ ] Literal optimizations and just general performance improvements.

Supports Zig 0.15.1.

## Usage

```zig
const debug = @import("std").debug;
const Regex = @import("regex").Regex;

test "example" {
    var re = try Regex.compile(debug.global_allocator, "\\w+");

    debug.assert(try re.match("hej") == true);
}
```

## Api

### Regex

```zig
fn compile(a: Allocator, re: []const u8) !Regex
```

Compiles a regex string, returning any errors during parsing/compiling.

---

```zig
pub fn match(re: *Regex, input: []const u8) !bool
```

Match a compiled regex against some input. The input must be matched in its
entirety and from the first index.

---

```zig
pub fn partialMatch(re: *Regex, input: []const u8) !bool
```

Match a compiled regex against some input. Unlike `match`, this matches the
leftmost and does not have to be anchored to the start of `input`.

---

```zig
pub fn captures(re: *Regex, input: []const u8) !?Captures
```

Match a compiled regex against some input. Returns a list of all matching
slices in the regex with the first (0-index) being the entire regex.

If no match was found, null is returned.

### Captures

```zig
pub fn sliceAt(captures: *const Captures, n: usize) ?[]const u8
```

Return the sub-slice for the numbered capture group. 0 refers to the entire
match.

```zig
pub fn boundsAt(captures: *const Captures, n: usize) ?Span
```

Return the lower and upper byte positions for the specified capture group.

We can retrieve the sub-slice using this function:

```zig
const span = caps.boundsAt(0)
debug.assert(mem.eql(u8, caps.sliceAt(0), input[span.lower..span.upper]));
```

---

## References

See the following useful sources:
 - https://swtch.com/~rsc/regexp/
 - [Rust Regex Library](https://github.com/rust-lang/regex)
 - [Go Regex Library](https://github.com/golang/go/tree/master/src/regexp)