README.md — sigil-peg

1# sigil-peg

PEG (Parsing Expression Grammar) library for [Sigil](https://codeberg.org/sigil/sigil). Represent patterns as S-expressions with a capture stack for structured output. Inspired by Janet's PEG module.

5## Usage

7```scheme

8(import (sigil peg))

10;; Match a literal string

11(peg/match '(seq "hello" " " "world") "hello world")

12; => #<peg-match 0..11 ()>

14;; Capture matched text

15(peg-match-captures (peg/match '(<- (* (char-set char-alphabetic?))) "hello"))

16; => ("hello")

18;; Define a grammar with named rules

19(define-grammar csv

20 (main (* (seq 'field (? (seq "," 'field)) 'newline))

21 (field (<- (+ (! ",") (! "\n") any-char)))

22 (newline (/ "\n" (input-end))))

23```

25## Pattern Language

27- **Atomic:** `"literal"`, `#\char`, `'rule-ref`, `any-char`, `(char-range #\a #\z)`, `(char-set char-alphabetic?)`

- **Combinators:** `(seq p ...)`, `(/ p ...)`, `(* p)`, `(+ p)`, `(? p)`, `(! p)`, `(& p)`, `(to p)`, `(thru p)`, `(between min max p)`

- **Captures:** `(<- p)`, `(<- p tag)`, `(group p)`, `(position)`, `(constant val)`, `(cmt p fn)`, `(drop p)`, `(backref tag)`, `(replace p val)`

30- **Anchors:** `(line-start)`, `(line-end)`, `(input-start)`, `(input-end)`

32## Dependencies

34- sigil-stdlib

36## Build

38```sh

39sigil build

40sigil test

41```

43## License

45BSD-3-Clause