ParseIt

Description

This library provides a very simple and lightweight parser (recursive descendant ll(1)) to combine and express a grammar.

The library uses Logos as a lexical analyzer and tokenizer.

The premise

This library major incentives were:

• lightweight : very small and does not require a deep dive
• transparency : literally 3 structs with a handful of methods
• speed : good speed (with a gratitude to Logos)

The steps to implement

Create a set of tokens using Logos

Add logos to dependency

cargo logos = "*"

```rust use logos::Logos;

[derive(Logos, Debug, PartialEq)]

enum Token { // Tokens can be literal strings, of any length. #[token("fast")] Fast,

#[token(".")]
Period,

// Or regular expressions.
#[regex("[a-zA-Z]+")]
Text,

// Logos requires one token variant to handle errors,
// it can be named anything you wish.
#[error]
// We can also use this variant to define whitespace,
// or any other matches we wish to skip.
#[regex(r"[ \t\n\f]+", logos::skip)]
Error,

} ```

Create a parser that will be able to parse the given set of tokens

The library provides ParseIt<'a,T> instance that encompasses a set of tokens and auxiliary methods

```rust

struct Parser<'a> { inner: ParseIt<'a, Token<'a>>, }

```

Implement a parsing functions using ParseIt instance and auxiliary methods from the Step

The helpers:

• the macros token! that alleviates comparing and matching single tokens
• methods then, then_zip and others from Step
• methods one_or_more, zero_or_more from ParseIt

Transform the result into Result<Structure, ParserError<'a>>

rust fn text(&self, pos: usize) -> Result<Vec<Sentence<'a>>, ParseError<'a>> { self.inner.zero_or_more(pos, |p| self.sentence(p)).into() }

Complete example

```rust use crate::parser::ParseIt; use crate::token; use crate::step::Step; use crate::parser::EmptyToken; use crate::error::ParseError; use logos::Logos;

[derive(Logos, Debug, Copy, Clone, PartialEq)]

pub enum Token<'a> { #[regex(r"[a-zA-Z-]+")] Word(&'a str),

#[token(",")]
Comma,
#[token(".")]
Dot,

#[token("!")]
Bang,
#[token("?")]
Question,

#[regex(r"[ \t\r\n\u000C\f]+", logos::skip)]
Whitespace,
#[error]
Error,

}

[derive(Debug, Copy, Clone, PartialEq)]

enum Item<'a> { Word(&'a str), Comma, }

[derive(Debug, Clone, PartialEq)]

enum Sentence<'a> { Sentence(Vec>), Question(Vec>), Exclamation(Vec>), }

struct Parser<'a> { inner: ParseIt<'a, Token<'a>>, }

impl<'a> Parser<'a> { fn new(text: &'a str) -> Parser<'a> { let delegate: ParseIt = ParseIt::new(text).unwrap(); Parser { inner: delegate } }

fn sentence(&self, pos: usize) -> Step<'a, Sentence<'a>> {
    let items = |p| self.inner.one_or_more(p, |p| self.word(p));

    let sentence = |p| items(p)
        .then_zip(|p| token!(self.inner.token(p) => Token::Dot))
        .take_left()
        .map(Sentence::Sentence);

    let exclamation = |p| items(p)
        .then_zip(|p| token!(self.inner.token(p) => Token::Bang))
        .take_left()
        .map(Sentence::Exclamation);
    let question = |p| items(p)
        .then_zip(|p| token!(self.inner.token(p) => Token::Question))
        .take_left()
        .map(Sentence::Question);

    sentence(pos)
        .or_from(pos)
        .or(exclamation)
        .or(question)
        .into()
}
fn word(&self, pos: usize) -> Step<'a, Item<'a>> {
    token!(self.inner.token(pos) =>
                 Token::Word(v) => Item::Word(v),
                 Token::Comma => Item::Comma
        )
}
fn text(&self, pos: usize) -> Result<Vec<Sentence<'a>>, ParseError<'a>> {
    self.inner.zero_or_more(pos, |p| self.sentence(p)).into()
}

}

[test]

fn test() { let parser = Parser::new(r#" I have a strange addiction, It often sets off sparks! I really cannot seem to stop, Using exclamation marks! Anyone heard of the interrobang? The poem is for kids. "#);

let result = parser.text(0).unwrap();
println!("{:?}", result);

} ```

The base auxiliary methods

On parser

• token - gives a possibility to pull out a curren token
• one_or_more - gives a one or more semantic
• zero_or_more - gives a zero or more semantic
• validate_eof - ensure the parser reaches end of the input

Macros

• token! - parses the current token. In general, it is used the following token!(p.token(pos) => T::Bang => "!")
• wrap! - implements a simple pattern in grammar like left value right, for instance [1,2,3] or (a,b)
  • can handle the default value like wrap!(0 => left; value or default; right)
  • can handle the option value like wrap!(0 => left; value ?; right)
• seq! - implements a simple pattern of sequence like el sep el ..., for instance 1,2,3
  • can have a , at the end signaling the separator can be at the ned of the seq like 1,2,3 (,)?

On step

To alternate

• or - gives an alternative in a horizon of one token
• or_from - gives a backtracking option

To combine

• then - gives a basic combination with a next rule omitting the current one
• then_zip - combines a current result and a next one into a pair
• then_skip - parses the next one but drops the result keeping only current one
• then_or_none -combines a next one in an option with a current one or return a none otherwise

To collect

• take_left - drops a right value from a pair
• take_right - drops a left value from a pair
• merge - merge a value into a list
• to_map - transforms a list of pairs into a map

To transform

• or_val - replaces a value with a default value if it is not presented
• or_none - replaces a value with a none if it is not presented

To work with value

• ok - transforms a value into an option
• error - transforms an error into an option
• map - transforms a value
• combine - combines a value with another value from a given step
• validate - validates a given value and transforms into an error if a validation failed

To print

• print - print a step
• print_with - print a step with a given prefix
• print_as - print a step with a transformation of value
• print_with_as - print a step with a transformation of value with a given prefix
• parit.env - Prints a position and env from the source text(with a radius 2 and '>>' '<<' separating the offending token )

Testing

Lexer

To test a lexer there are methods from crate::parsit::test::lexer_test::* for service

```rust use logos::Logos; use crate::parsit::test::lexer_test::*;

[derive(Logos, Debug, PartialEq)]

pub enum T<'a> { #[regex(r"[a-zA-Z-]+")] Word(&'a str),

#[token(",")]
Comma,
#[token(".")]
Dot,

#[token("!")]
Bang,
#[token("?")]
Question,

#[regex(r"[ \t\r\n]+", logos::skip)]
Whitespace,
#[error]
Error,

}

[test]

fn test() { expect::("abc, bcs!", vec![T::Word("abc"), T::Comma, T::Word("bcs"), T::Bang]); expectsucceed::("abc, bcs!"); expectfailed::("abc, bcs >> !"); expectfailedwith::("abc, bcs > !", |e| e.isbadtoken_on(">")); } ```

Parser

To test a parser there are methods from crate::parsit::test::parser_test::* for service

```rust use logos::Logos; use crate::parsit::test::parsertest::fail; use crate::parsit::test::parsertest::parsit; use crate::parsit::token; use crate::parsit::parser::ParseIt; use crate::parsit::step::Step;

[derive(Logos, Debug, PartialEq)]

pub enum T<'a> { #[regex(r"[a-zA-Z-]+")] Word(&'a str),

#[token(",")]
Comma,
#[token(".")]
Dot,

#[token("!")]
Bang,
#[token("?")]
Question,

#[regex(r"[ \t\r\n]+", logos::skip)]
Whitespace,
#[error]
Error,

}

[test]

fn testexpect() { let p = parsit("abc!"); let bang = |pos: usize| token!(p.token(pos) => T::Bang => "!"); let word = |pos: usize| token!(p.token(pos) => T::Word(v) => *v); let step = word(0) .thenorvalzip(bang, "") .map(|(a, b)| format!("{}{}", a, b));

expect(step, "abc!".to_string());

}

[test]

fn testpos() { let p = parsit("abc!"); let bang = |pos: usize| token!(p.token(pos) => T::Bang => "!"); let word = |pos: usize| token!(p.token(pos) => T::Word(v) => v); let step = word(0).thenorvalzip(bang, "");

expect_pos(step, 2); // the next position to parse

}

[test]

fn testfail() { let p = parsit("abc?!"); let bang = |pos: usize| token!(p.token(pos) => T::Bang => "!"); let word = |pos: usize| token!(p.token(pos) => T::Word(v) => v); let step = word(0).thenzip(bang);

fail(step);

}

[test]

fn testfailon() { let p = parsit("abc?!"); let bang = |pos: usize| token!(p.token(pos) => T::Bang => "!"); let word = |pos: usize| token!(p.token(pos) => T::Word(v) => v); let step = word(0).then_zip(bang);

fail_on(step, 1);

}

```