mirror of https://github.com/helix-editor/helix
Add a parser-combinator crate
Parser-combinators are one of the simpler tools for building ad-hoc parsers. They're a good fit because they are... * Small: each parser / parser-combinator is around 10 LOC. * Functional: helix_core strives to be a functional set of utilities usable throughout the rest of the editor. * Flexible: use them to build any sort of ad-hoc parser. In the child commit, we'll parse LSP Snippet syntax using these new parser combinators. Why not use an existing parser-combinator crate? Existing popular parser-combinator crates have histories of making breaking changes (for example nom and combine). > Implementation note: I tried to not introduce a new trait since the > types can be expressed in terms of `impl Fn`s. The trait is necessary > to build `seq` implementations without a proc macro though, and also > allows us to use `&'static str`s very conveniently: see the trait > implementation for `&'static str`.pull/5465/merge
Michael Davis
2 years ago
committed by
Blaž Hrastnik
parent
f976c004e2
commit
c8e6857aff
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[package]
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name = "helix-parsec"
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version = "0.6.0"
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authors = ["Blaž Hrastnik <blaz@mxxn.io>"]
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edition = "2021"
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license = "MPL-2.0"
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description = "Parser combinators for Helix"
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categories = ["editor"]
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repository = "https://github.com/helix-editor/helix"
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homepage = "https://helix-editor.com"
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include = ["src/**/*", "README.md"]
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[dependencies]
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regex = "1"
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@ -0,0 +1,560 @@
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//! Parser-combinator functions
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//!
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//! This module provides parsers and parser combinators which can be used
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//! together to build parsers by functional composition.
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use regex::Regex;
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// This module implements parser combinators following https://bodil.lol/parser-combinators/.
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// `sym` (trait implementation for `&'static str`), `map`, `pred` (filter), `one_or_more`,
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// `zero_or_more`, as well as the `Parser` trait originate mostly from that post.
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// The remaining parsers and parser combinators are either based on
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// https://github.com/archseer/snippets.nvim/blob/a583da6ef130d2a4888510afd8c4e5ffd62d0dce/lua/snippet/parser.lua#L5-L138
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// or are novel.
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// When a parser matches the input successfully, it returns `Ok((next_input, some_value))`
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// where the type of the returned value depends on the parser. If the parser fails to match,
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// it returns `Err(input)`.
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type ParseResult<'a, Output> = Result<(&'a str, Output), &'a str>;
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/// A parser or parser-combinator.
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///
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/// Parser-combinators compose multiple parsers together to parse input.
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/// For example, two basic parsers (`&'static str`s) may be combined with
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/// a parser-combinator like [or] to produce a new parser.
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///
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/// ```
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/// use helix_parsec::{or, Parser};
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/// let foo = "foo"; // matches "foo" literally
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/// let bar = "bar"; // matches "bar" literally
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/// let foo_or_bar = or(foo, bar); // matches either "foo" or "bar"
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/// assert_eq!(Ok(("", "foo")), foo_or_bar.parse("foo"));
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/// assert_eq!(Ok(("", "bar")), foo_or_bar.parse("bar"));
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/// assert_eq!(Err("baz"), foo_or_bar.parse("baz"));
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/// ```
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pub trait Parser<'a> {
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type Output;
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fn parse(&self, input: &'a str) -> ParseResult<'a, Self::Output>;
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}
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// Most parser-combinators are written as higher-order functions which take some
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// parser(s) as input and return a new parser: a function that takes input and returns
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// a parse result. The underlying implementation of [Parser::parse] for these functions
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// is simply application.
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#[doc(hidden)]
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impl<'a, F, T> Parser<'a> for F
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where
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F: Fn(&'a str) -> ParseResult<T>,
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{
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type Output = T;
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fn parse(&self, input: &'a str) -> ParseResult<'a, Self::Output> {
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self(input)
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}
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}
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/// A parser which matches the string literal exactly.
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///
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/// This parser succeeds if the next characters in the input are equal to the given
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/// string literal.
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///
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/// Note that [str::parse] interferes with calling [Parser::parse] on string literals
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/// directly; this trait implementation works when used within any parser combinator
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/// but does not work on its own. To call [Parser::parse] on a parser for a string
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/// literal, use the [token] parser.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{or, Parser};
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/// let parser = or("foo", "bar");
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/// assert_eq!(Ok(("", "foo")), parser.parse("foo"));
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/// assert_eq!(Ok(("", "bar")), parser.parse("bar"));
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/// assert_eq!(Err("baz"), parser.parse("baz"));
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/// ```
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impl<'a> Parser<'a> for &'static str {
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type Output = &'a str;
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fn parse(&self, input: &'a str) -> ParseResult<'a, Self::Output> {
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match input.get(0..self.len()) {
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Some(actual) if actual == *self => Ok((&input[self.len()..], &input[0..self.len()])),
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_ => Err(input),
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}
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}
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}
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// Parsers
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/// A parser which matches the given string literally.
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///
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/// This function is a convenience for interpreting string literals as parsers
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/// and is only necessary to avoid conflict with [str::parse]. See the documentation
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/// for the `&'static str` implementation of [Parser].
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{token, Parser};
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/// let parser = token("foo");
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/// assert_eq!(Ok(("", "foo")), parser.parse("foo"));
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/// assert_eq!(Err("bar"), parser.parse("bar"));
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/// ```
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pub fn token<'a>(literal: &'static str) -> impl Parser<'a, Output = &'a str> {
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literal
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}
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/// A parser which matches the pattern described by the given regular expression.
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///
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/// The pattern must match from the beginning of the input as if the regular expression
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/// included the `^` anchor. Using a `^` anchor in the regular expression is
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/// recommended in order to reduce any work done by the regex on non-matching input.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{pattern, Parser};
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/// use regex::Regex;
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/// let regex = Regex::new(r"Hello, \w+!").unwrap();
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/// let parser = pattern(®ex);
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/// assert_eq!(Ok(("", "Hello, world!")), parser.parse("Hello, world!"));
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/// assert_eq!(Err("Hey, you!"), parser.parse("Hey, you!"));
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/// assert_eq!(Err("Oh Hello, world!"), parser.parse("Oh Hello, world!"));
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/// ```
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pub fn pattern<'a>(regex: &'a Regex) -> impl Parser<'a, Output = &'a str> {
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move |input: &'a str| match regex.find(input) {
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Some(match_) if match_.start() == 0 => {
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Ok((&input[match_.end()..], &input[0..match_.end()]))
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}
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_ => Err(input),
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}
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}
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/// A parser which matches all values until the specified pattern is found.
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///
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/// If the pattern is not found, this parser does not match. The input up to the
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/// character which returns `true` is returned but not that character itself.
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///
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/// If the pattern function returns true on the first input character, this
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/// parser fails.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{take_until, Parser};
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/// let parser = take_until(|c| c == '.');
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/// assert_eq!(Ok((".bar", "foo")), parser.parse("foo.bar"));
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/// assert_eq!(Err(".foo"), parser.parse(".foo"));
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/// assert_eq!(Err("foo"), parser.parse("foo"));
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/// ```
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pub fn take_until<'a, F>(pattern: F) -> impl Parser<'a, Output = &'a str>
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where
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F: Fn(char) -> bool,
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{
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move |input: &'a str| match input.find(&pattern) {
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Some(index) if index != 0 => Ok((&input[index..], &input[0..index])),
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_ => Err(input),
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}
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}
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// Variadic parser combinators
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/// A parser combinator which matches a sequence of parsers in an all-or-nothing fashion.
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///
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/// The returned value is a tuple containing the outputs of all parsers in order. Each
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/// parser in the sequence may be typed differently.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{seq, Parser};
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/// let parser = seq!("<", "a", ">");
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/// assert_eq!(Ok(("", ("<", "a", ">"))), parser.parse("<a>"));
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/// assert_eq!(Err("<b>"), parser.parse("<b>"));
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/// ```
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#[macro_export]
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macro_rules! seq {
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($($parsers: expr),+ $(,)?) => {
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($($parsers),+)
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}
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}
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// Seq is implemented using trait-implementations of Parser for various size tuples.
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// This allows sequences to be typed heterogeneously.
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macro_rules! seq_impl {
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($($parser:ident),+) => {
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#[allow(non_snake_case)]
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impl<'a, $($parser),+> Parser<'a> for ($($parser),+)
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where
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$($parser: Parser<'a>),+
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{
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type Output = ($($parser::Output),+);
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fn parse(&self, input: &'a str) -> ParseResult<'a, Self::Output> {
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let ($($parser),+) = self;
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seq_body_impl!(input, input, $($parser),+ ; )
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}
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}
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}
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}
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macro_rules! seq_body_impl {
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($input:expr, $next_input:expr, $head:ident, $($tail:ident),+ ; $(,)? $($acc:ident),*) => {
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match $head.parse($next_input) {
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Ok((next_input, $head)) => seq_body_impl!($input, next_input, $($tail),+ ; $($acc),*, $head),
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Err(_) => Err($input),
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}
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};
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($input:expr, $next_input:expr, $last:ident ; $(,)? $($acc:ident),*) => {
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match $last.parse($next_input) {
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Ok((next_input, last)) => Ok((next_input, ($($acc),+, last))),
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Err(_) => Err($input),
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}
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}
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}
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seq_impl!(A, B);
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seq_impl!(A, B, C);
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seq_impl!(A, B, C, D);
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seq_impl!(A, B, C, D, E);
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seq_impl!(A, B, C, D, E, F);
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seq_impl!(A, B, C, D, E, F, G);
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seq_impl!(A, B, C, D, E, F, G, H);
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seq_impl!(A, B, C, D, E, F, G, H, I);
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seq_impl!(A, B, C, D, E, F, G, H, I, J);
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/// A parser combinator which chooses the first of the input parsers which matches
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/// successfully.
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///
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/// All input parsers must have the same output type. This is a variadic form for [or].
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{choice, or, Parser};
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/// let parser = choice!("foo", "bar", "baz");
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/// assert_eq!(Ok(("", "foo")), parser.parse("foo"));
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/// assert_eq!(Ok(("", "bar")), parser.parse("bar"));
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/// assert_eq!(Err("quiz"), parser.parse("quiz"));
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/// ```
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#[macro_export]
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macro_rules! choice {
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($parser: expr $(,)?) => {
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$parser
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};
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($parser: expr, $($rest: expr),+ $(,)?) => {
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or($parser, choice!($($rest),+))
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}
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}
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// Ordinary parser combinators
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/// A parser combinator which takes a parser as input and maps the output using the
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/// given transformation function.
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///
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/// This corresponds to [Result::map]. The value is only mapped if the input parser
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/// matches against input.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{map, Parser};
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/// let parser = map("123", |s| s.parse::<i32>().unwrap());
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/// assert_eq!(Ok(("", 123)), parser.parse("123"));
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/// assert_eq!(Err("abc"), parser.parse("abc"));
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/// ```
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pub fn map<'a, P, F, T>(parser: P, map_fn: F) -> impl Parser<'a, Output = T>
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where
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P: Parser<'a>,
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F: Fn(P::Output) -> T,
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{
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move |input| {
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parser
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.parse(input)
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.map(|(next_input, result)| (next_input, map_fn(result)))
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}
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}
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/// A parser combinator which succeeds if the given parser matches the input and
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/// the given `filter_map_fn` returns `Some`.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{filter_map, take_until, Parser};
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/// let parser = filter_map(take_until(|c| c == '.'), |s| s.parse::<i32>().ok());
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/// assert_eq!(Ok((".456", 123)), parser.parse("123.456"));
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/// assert_eq!(Err("abc.def"), parser.parse("abc.def"));
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/// ```
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pub fn filter_map<'a, P, F, T>(parser: P, filter_map_fn: F) -> impl Parser<'a, Output = T>
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where
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P: Parser<'a>,
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F: Fn(P::Output) -> Option<T>,
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{
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move |input| match parser.parse(input) {
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Ok((next_input, value)) => match filter_map_fn(value) {
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Some(value) => Ok((next_input, value)),
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None => Err(input),
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},
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Err(_) => Err(input),
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}
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}
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/// A parser combinator which succeeds if the first given parser matches the input and
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/// the second given parse also matches.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{reparse_as, take_until, one_or_more, Parser};
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/// let parser = reparse_as(take_until(|c| c == '/'), one_or_more("a"));
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/// assert_eq!(Ok(("/bb", vec!["a", "a"])), parser.parse("aa/bb"));
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/// ```
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pub fn reparse_as<'a, P1, P2, T>(parser1: P1, parser2: P2) -> impl Parser<'a, Output = T>
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where
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P1: Parser<'a, Output = &'a str>,
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P2: Parser<'a, Output = T>,
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{
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filter_map(parser1, move |str| {
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parser2.parse(str).map(|(_, value)| value).ok()
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})
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}
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/// A parser combinator which only matches the input when the predicate function
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/// returns true.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{filter, take_until, Parser};
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/// let parser = filter(take_until(|c| c == '.'), |s| s == &"123");
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/// assert_eq!(Ok((".456", "123")), parser.parse("123.456"));
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/// assert_eq!(Err("456.123"), parser.parse("456.123"));
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/// ```
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pub fn filter<'a, P, F, T>(parser: P, pred_fn: F) -> impl Parser<'a, Output = T>
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where
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P: Parser<'a, Output = T>,
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F: Fn(&P::Output) -> bool,
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{
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move |input| {
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if let Ok((next_input, value)) = parser.parse(input) {
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if pred_fn(&value) {
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return Ok((next_input, value));
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}
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}
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Err(input)
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}
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}
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/// A parser combinator which matches either of the input parsers.
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///
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/// Both parsers must have the same output type. For a variadic form which
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/// can take any number of parsers, use `choice!`.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{or, Parser};
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/// let parser = or("foo", "bar");
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/// assert_eq!(Ok(("", "foo")), parser.parse("foo"));
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/// assert_eq!(Ok(("", "bar")), parser.parse("bar"));
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/// assert_eq!(Err("baz"), parser.parse("baz"));
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/// ```
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pub fn or<'a, P1, P2, T>(parser1: P1, parser2: P2) -> impl Parser<'a, Output = T>
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where
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P1: Parser<'a, Output = T>,
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P2: Parser<'a, Output = T>,
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{
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move |input| match parser1.parse(input) {
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ok @ Ok(_) => ok,
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Err(_) => parser2.parse(input),
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}
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}
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/// A parser combinator which attempts to match the given parser, returning a
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/// `None` output value if the parser does not match.
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///
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/// The parser produced with this combinator always succeeds. If the given parser
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/// succeeds, `Some(value)` is returned where `value` is the output of the given
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/// parser. Otherwise, `None`.
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///
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/// # Examples
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///
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/// ```
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/// use helix_parsec::{optional, Parser};
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/// let parser = optional("foo");
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/// assert_eq!(Ok(("bar", Some("foo"))), parser.parse("foobar"));
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/// assert_eq!(Ok(("bar", None)), parser.parse("bar"));
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/// ```
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pub fn optional<'a, P, T>(parser: P) -> impl Parser<'a, Output = Option<T>>
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where
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P: Parser<'a, Output = T>,
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{
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move |input| match parser.parse(input) {
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Ok((next_input, value)) => Ok((next_input, Some(value))),
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Err(_) => Ok((input, None)),
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}
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}
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/// A parser combinator which runs the given parsers in sequence and returns the
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/// value of `left` if both are matched.
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///
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/// This is useful for two-element sequences in which you only want the output
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/// value of the `left` parser.
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///
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/// # Examples
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||||
///
|
||||
/// ```
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/// use helix_parsec::{left, Parser};
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/// let parser = left("foo", "bar");
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/// assert_eq!(Ok(("", "foo")), parser.parse("foobar"));
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/// ```
|
||||
pub fn left<'a, L, R, T>(left: L, right: R) -> impl Parser<'a, Output = T>
|
||||
where
|
||||
L: Parser<'a, Output = T>,
|
||||
R: Parser<'a>,
|
||||
{
|
||||
map(seq!(left, right), |(left_value, _)| left_value)
|
||||
}
|
||||
|
||||
/// A parser combinator which runs the given parsers in sequence and returns the
|
||||
/// value of `right` if both are matched.
|
||||
///
|
||||
/// This is useful for two-element sequences in which you only want the output
|
||||
/// value of the `right` parser.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use helix_parsec::{right, Parser};
|
||||
/// let parser = right("foo", "bar");
|
||||
/// assert_eq!(Ok(("", "bar")), parser.parse("foobar"));
|
||||
/// ```
|
||||
pub fn right<'a, L, R, T>(left: L, right: R) -> impl Parser<'a, Output = T>
|
||||
where
|
||||
L: Parser<'a>,
|
||||
R: Parser<'a, Output = T>,
|
||||
{
|
||||
map(seq!(left, right), |(_, right_value)| right_value)
|
||||
}
|
||||
|
||||
/// A parser combinator which matches the given parser against the input zero or
|
||||
/// more times.
|
||||
///
|
||||
/// This parser always succeeds and returns the empty Vec when it matched zero
|
||||
/// times.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use helix_parsec::{zero_or_more, Parser};
|
||||
/// let parser = zero_or_more("a");
|
||||
/// assert_eq!(Ok(("", vec![])), parser.parse(""));
|
||||
/// assert_eq!(Ok(("", vec!["a"])), parser.parse("a"));
|
||||
/// assert_eq!(Ok(("", vec!["a", "a"])), parser.parse("aa"));
|
||||
/// assert_eq!(Ok(("bb", vec![])), parser.parse("bb"));
|
||||
/// ```
|
||||
pub fn zero_or_more<'a, P, T>(parser: P) -> impl Parser<'a, Output = Vec<T>>
|
||||
where
|
||||
P: Parser<'a, Output = T>,
|
||||
{
|
||||
move |mut input| {
|
||||
let mut values = Vec::new();
|
||||
|
||||
while let Ok((next_input, value)) = parser.parse(input) {
|
||||
input = next_input;
|
||||
values.push(value);
|
||||
}
|
||||
|
||||
Ok((input, values))
|
||||
}
|
||||
}
|
||||
|
||||
/// A parser combinator which matches the given parser against the input one or
|
||||
/// more times.
|
||||
///
|
||||
/// This parser combinator acts the same as [zero_or_more] but must match at
|
||||
/// least once.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use helix_parsec::{one_or_more, Parser};
|
||||
/// let parser = one_or_more("a");
|
||||
/// assert_eq!(Err(""), parser.parse(""));
|
||||
/// assert_eq!(Ok(("", vec!["a"])), parser.parse("a"));
|
||||
/// assert_eq!(Ok(("", vec!["a", "a"])), parser.parse("aa"));
|
||||
/// assert_eq!(Err("bb"), parser.parse("bb"));
|
||||
/// ```
|
||||
pub fn one_or_more<'a, P, T>(parser: P) -> impl Parser<'a, Output = Vec<T>>
|
||||
where
|
||||
P: Parser<'a, Output = T>,
|
||||
{
|
||||
move |mut input| {
|
||||
let mut values = Vec::new();
|
||||
|
||||
match parser.parse(input) {
|
||||
Ok((next_input, value)) => {
|
||||
input = next_input;
|
||||
values.push(value);
|
||||
}
|
||||
Err(err) => return Err(err),
|
||||
}
|
||||
|
||||
while let Ok((next_input, value)) = parser.parse(input) {
|
||||
input = next_input;
|
||||
values.push(value);
|
||||
}
|
||||
|
||||
Ok((input, values))
|
||||
}
|
||||
}
|
||||
|
||||
/// A parser combinator which matches one or more instances of the given parser
|
||||
/// interspersed with the separator parser.
|
||||
///
|
||||
/// Output values of the separator parser are discarded.
|
||||
///
|
||||
/// This is typically used to parse function arguments or list items.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```rust
|
||||
/// use helix_parsec::{sep, Parser};
|
||||
/// let parser = sep("a", ",");
|
||||
/// assert_eq!(Ok(("", vec!["a", "a", "a"])), parser.parse("a,a,a"));
|
||||
/// ```
|
||||
pub fn sep<'a, P, S, T>(parser: P, separator: S) -> impl Parser<'a, Output = Vec<T>>
|
||||
where
|
||||
P: Parser<'a, Output = T>,
|
||||
S: Parser<'a>,
|
||||
{
|
||||
move |mut input| {
|
||||
let mut values = Vec::new();
|
||||
|
||||
match parser.parse(input) {
|
||||
Ok((next_input, value)) => {
|
||||
input = next_input;
|
||||
values.push(value);
|
||||
}
|
||||
Err(err) => return Err(err),
|
||||
}
|
||||
|
||||
loop {
|
||||
match separator.parse(input) {
|
||||
Ok((next_input, _)) => input = next_input,
|
||||
Err(_) => break,
|
||||
}
|
||||
|
||||
match parser.parse(input) {
|
||||
Ok((next_input, value)) => {
|
||||
input = next_input;
|
||||
values.push(value);
|
||||
}
|
||||
Err(_) => break,
|
||||
}
|
||||
}
|
||||
|
||||
Ok((input, values))
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue