Pears - A parser combinator library for Gleam

Installation

gleam add pears

Usage

import pears.{type Parser}
import pears/chars.{type Char, natural}
import pears/combinators.{between, lazy, map, or, sep_by0, token}

pub type Tree(a) {
  Leaf(a)
  Node(List(Tree(a)))
}

fn tree_parser(p: Parser(Char, a)) -> Parser(Char, Tree(a)) {
  let tree = lazy(fn() { tree_parser(p) })
  let leaf = map(p, Leaf)
  let node =
    tree
    |> sep_by0(token(","))
    |> between(token("["), token("]"))
    |> map(Node)
  or(leaf, node)
}

pub fn main() {
  let assert Ok(Node([Leaf(1), Node([Leaf(2), Leaf(3)]), Leaf(4)])) =
    pears.parse_string_all("[1,[2,3],4]", tree_parser(natural()))
}

chars.format_error turns a ParseError into a message:

let source = "[1,[2,3],4]x"
let assert Error(error) = pears.parse_string_all(source, tree_parser(natural()))

chars.format_error(error, source)
// => line 1, column 12: expected end of input, found "x"

Further documentation can be found at https://hexdocs.pm/pears.

See the test directory for more examples.

Development

gleam test               # Run the tests, including doc examples (via gleedoc)
gleam run -m pears_bench # Run the benchmarks
gleam shell              # Run an Erlang shell

Add --target javascript to run the tests or benchmarks on JavaScript.