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//! # Minimal Parsing Language (MPL)
//!
//! [](https://crates.io/crates/mpl)
//! [](https://docs.rs/mpl)
//!
//! This is minimal parser combinator of Minimal Parsing Language (MPL) like Top-Down Parsing Language (TDPL). It creates a abstract syntax tree (AST) for each input.
//!
//! ## Getting Started
//! 1. implement `Variable`
//! 2. insert each rule into `HashMap`
//! 3. `minimal_parse()`
//!
//! - Optional
//! - implement `Input`
//! - supports `[T]` and `str` by default
//! - implement `Position`
//! - supports `u*`, `i*`, and `f*` by default
//! - implement `Span`
//! - supports `StartAndLenSpan` by default
//! - implement `Terminal`
//! - supports `SliceTerminal`, `StrTerminal`, and `U8SliceTerminal` by default
//! - implement `Output`
//! - supports `()` by default
//! - implement `Rules`
//! - supports `HashMap` by default
//! - implement `Parse`
//! - supports `[T]`, `str`, and `[u8]` by default
//!
//! ### Example
//! ```rust
//! use crate::ParenthesesVariable::*;
//! use mpl::parser::Parser;
//! use mpl::rules::{RightRule, RightRuleKind::*, Rules};
//! use mpl::span::{StartAndLenSpan, Start, Len};
//! use mpl::output::Output;
//! use mpl::symbols::{StrTerminal, StrTerminal::*, Variable};
//! use mpl::trees::AST;
//! use std::collections::HashMap;
//!
//! #[derive(Clone, Debug, Hash, Eq, PartialEq)]
//! enum ParenthesesVariable {
//! Open,
//! Parentheses,
//! Close,
//! }
//!
//! impl Variable for ParenthesesVariable {}
//!
//! struct ParenthesesParser;
//!
//! impl<'i, V, P, L, R, O> Parser<'i, str, StrTerminal<'i>, V, StartAndLenSpan<P, L>, P, R, O>
//! for ParenthesesParser
//! where
//! V: Variable,
//! P: Start<str, L>,
//! L: Len<str, P>,
//! R: Rules<StrTerminal<'i>, V>,
//! O: Output<'i, str, V, StartAndLenSpan<P, L>>,
//! {
//! }
//!
//! /// ```
//! /// Open = '(' Parentheses / ()
//! /// Parentheses = Open Close / f
//! /// Close = ")" Open / f
//! /// ```
//! fn main() {
//! let parser = ParenthesesParser;
//! let mut rules = HashMap::new();
//!
//! rules.insert(
//! Open,
//! RightRule::from_right_rule_kind((T(Char('(')), V(Parentheses)), Empty),
//! );
//! rules.insert(
//! Parentheses,
//! RightRule::from_right_rule_kind((V(Open), V(Close)), Failure),
//! );
//! rules.insert(
//! Close,
//! RightRule::from_right_rule_kind((T(Str(")")), V(Open)), Failure),
//! );
//!
//! let input = "(()(()))";
//!
//! // all of the span
//! let all_of_the_span = StartAndLenSpan::<u32, u16>::from_start_len(0, input.len() as u16);
//!
//! let result: Result<
//! AST<ParenthesesVariable, StartAndLenSpan<u32, u16>, ()>,
//! AST<ParenthesesVariable, StartAndLenSpan<u32, u16>, ()>,
//! > = parser.parse(input, &rules, &Open, &all_of_the_span);
//!
//! if let Ok(ast) = result {
//! println!("{}", ast);
//! }
//! }
//! ```
//!
//! ### Test Examples
//! - [Number](tests/number.rs)
//! - [Parentheses](tests/parentheses.rs)
//! - [Wav Riff](tests/wav_riff.rs)
//!
//! ### Parsers written with MPL
//! - [WAV AST](https://github.com/kurotakazuki/wav_ast) : RIFF waveform Audio Format
//!
//! ## MPL
//! ### Definition of MPL grammar
//! A MPL grammar `G` is a tuple `G = (V, Σ, R, S)` in which:
//! - `V` is a finite set of variables.
//! - `Σ` is a finite set of original terminal symbols.
//! - `T` is an union of `Σ` or `M` (Σ ∪ M) (`M` (= {(), f}) is a finite set of metasymbols).
//! - `R` is a finite set of rules of the form
//! - `A = B C / D`
//! A in V (A ∈ V),
//! B, C, D in E (E = T ∪ V) (T ∩ V = ∅) (B, C, D ∈ E).
//! For any variable A there is exactly one rule with A to the left of `=`.
//! - S in V (S ∈ V) is the start variable.
//!
//! #### Empty
//! `()` is a metasymbol that always succeeds without consuming input.
//!
//! ```rust ignore
//! Empty = () () / ()
//! ```
//!
//! #### Failure
//! `f` is a metasymbol that always fails without consuming input.
//!
//! ```rust ignore
//! Failure = f f / f
//! ```
//!
//! ### Extended MPL
//! Since one of the goals of MPL is to create an AST, it also supports two features in terms of ease of use and speed.
//!
//! #### Any
//! `?` is a metasymbol representing any single input like wildcard character. This succeeds if there is any input left, and fails if there is no input left.
//!
//! ```rust ignore
//! Any = ? () / f
//! ```
//!
//! To extend the difinition of MPL grammar, let ? ∈ M.
//!
//! #### All
//! `*` is a metasymbol representing All remaining input like wildcard character. This will succeed even if the remaining inputs are zero.
//!
//! ```rust ignore
//! All = * () / f
//! ```
//!
//! Same as `All = ? All / ()`.
//!
//! To extend the difinition of MPL grammar, let * ∈ M.