// pest. The Elegant Parser // Copyright (c) 2018 Dragoș Tiselice // // Licensed under the Apache License, Version 2.0 // or the MIT // license , at your // option. All files in the project carrying such notice may not be copied, // modified, or distributed except according to those terms. //! # pest. The Elegant Parser //! //! pest is a general purpose parser written in Rust with a focus on accessibility, correctness, //! and performance. It uses parsing expression grammars (or [PEG]) as input, which are similar in //! spirit to regular expressions, but which offer the enhanced expressivity needed to parse //! complex languages. //! //! [PEG]: https://en.wikipedia.org/wiki/Parsing_expression_grammar //! //! ## Getting started //! //! The recommended way to start parsing with pest is to read the official [book]. //! //! Other helpful resources: //! //! * API reference on [docs.rs] //! * play with grammars and share them on our [fiddle] //! * leave feedback, ask questions, or greet us on [Gitter] //! //! [book]: https://pest-parser.github.io/book //! [docs.rs]: https://docs.rs/pest //! [fiddle]: https://pest-parser.github.io/#editor //! [Gitter]: https://gitter.im/dragostis/pest //! //! ## `.pest` files //! //! Grammar definitions reside in custom `.pest` files located in the `src` directory. Their path is //! relative to `src` and is specified between the `derive` attribute and empty `struct` that //! `Parser` will be derived on. //! //! ```ignore //! #[derive(Parser)] //! #[grammar = "path/to/my_grammar.pest"] // relative to src //! struct MyParser; //! ``` //! //! ## Inline grammars //! //! Grammars can also be inlined by using the `#[grammar_inline = "..."]` attribute. //! //! ## Grammar //! //! A grammar is a series of rules separated by whitespace, possibly containing comments. //! //! ### Comments //! //! Comments start with `//` and end at the end of the line. //! //! ```text //! // a comment //! ``` //! //! ### Rules //! //! Rules have the following form: //! //! ```ignore //! name = optional_modifier { expression } //! ``` //! //! The name of the rule is formed from alphanumeric characters or `_` with the condition that the //! first character is not a digit and is used to create token pairs. When the rule starts being //! parsed, the starting part of the token is being produced, with the ending part being produced //! when the rule finishes parsing. //! //! The following token pair notation `a(b(), c())` denotes the tokens: start `a`, start `b`, end //! `b`, start `c`, end `c`, end `a`. //! //! #### Modifiers //! //! Modifiers are optional and can be one of `_`, `@`, `$`, or `!`. These modifiers change the //! behavior of the rules. //! //! 1. Silent (`_`) //! //! Silent rules do not create token pairs during parsing, nor are they error-reported. //! //! ```ignore //! a = _{ "a" } //! b = { a ~ "b" } //! ``` //! //! Parsing `"ab"` produces the token pair `b()`. //! //! 2. Atomic (`@`) //! //! Atomic rules do not accept whitespace or comments within their expressions and have a //! cascading effect on any rule they call. I.e. rules that are not atomic but are called by atomic //! rules behave atomically. //! //! Any rules called by atomic rules do not generate token pairs. //! //! ```ignore //! a = { "a" } //! b = @{ a ~ "b" } //! //! WHITESPACE = _{ " " } //! ``` //! //! Parsing `"ab"` produces the token pair `b()`, while `"a b"` produces an error. //! //! 3. Compound-atomic (`$`) //! //! Compound-atomic are identical to atomic rules with the exception that rules called by them are //! not forbidden from generating token pairs. //! //! ```ignore //! a = { "a" } //! b = ${ a ~ "b" } //! //! WHITESPACE = _{ " " } //! ``` //! //! Parsing `"ab"` produces the token pairs `b(a())`, while `"a b"` produces an error. //! //! 4. Non-atomic (`!`) //! //! Non-atomic are identical to normal rules with the exception that they stop the cascading effect //! of atomic and compound-atomic rules. //! //! ```ignore //! a = { "a" } //! b = !{ a ~ "b" } //! c = @{ b } //! //! WHITESPACE = _{ " " } //! ``` //! //! Parsing both `"ab"` and `"a b"` produce the token pairs `c(a())`. //! //! #### Expressions //! //! Expressions can be either terminals or non-terminals. //! //! 1. Terminals //! //! | Terminal | Usage | //! |------------|----------------------------------------------------------------| //! | `"a"` | matches the exact string `"a"` | //! | `^"a"` | matches the exact string `"a"` case insensitively (ASCII only) | //! | `'a'..'z'` | matches one character between `'a'` and `'z'` | //! | `a` | matches rule `a` | //! //! Strings and characters follow //! [Rust's escape mechanisms](https://doc.rust-lang.org/reference/tokens.html#byte-escapes), while //! identifiers can contain alphanumeric characters and underscores (`_`), as long as they do not //! start with a digit. //! //! 2. Non-terminals //! //! | Non-terminal | Usage | //! |-----------------------|------------------------------------------------------------| //! | `(e)` | matches `e` | //! | `e1 ~ e2` | matches the sequence `e1` `e2` | //! | e1 \| e2 | matches either `e1` or `e2` | //! | `e*` | matches `e` zero or more times | //! | `e+` | matches `e` one or more times | //! | `e{n}` | matches `e` exactly `n` times | //! | `e{, n}` | matches `e` at most `n` times | //! | `e{n,} ` | matches `e` at least `n` times | //! | `e{m, n}` | matches `e` between `m` and `n` times inclusively | //! | `e?` | optionally matches `e` | //! | `&e` | matches `e` without making progress | //! | `!e` | matches if `e` doesn't match without making progress | //! | `PUSH(e)` | matches `e` and pushes it's captured string down the stack | //! //! where `e`, `e1`, and `e2` are expressions. //! //! Expressions can modify the stack only if they match the input. For example, //! if `e1` in the compound expression `e1 | e2` does not match the input, then //! it does not modify the stack, so `e2` sees the stack in the same state as //! `e1` did. Repetitions and optionals (`e*`, `e+`, `e{, n}`, `e{n,}`, //! `e{m,n}`, `e?`) can modify the stack each time `e` matches. The `!e` and `&e` //! expressions are a special case; they never modify the stack. //! //! ## Special rules //! //! Special rules can be called within the grammar. They are: //! //! * `WHITESPACE` - runs between rules and sub-rules //! * `COMMENT` - runs between rules and sub-rules //! * `ANY` - matches exactly one `char` //! * `SOI` - (start-of-input) matches only when a `Parser` is still at the starting position //! * `EOI` - (end-of-input) matches only when a `Parser` has reached its end //! * `POP` - pops a string from the stack and matches it //! * `POP_ALL` - pops the entire state of the stack and matches it //! * `PEEK` - peeks a string from the stack and matches it //! * `PEEK[a..b]` - peeks part of the stack and matches it //! * `PEEK_ALL` - peeks the entire state of the stack and matches it //! * `DROP` - drops the top of the stack (fails to match if the stack is empty) //! //! `WHITESPACE` and `COMMENT` should be defined manually if needed. All other rules cannot be //! overridden. //! //! ## `WHITESPACE` and `COMMENT` //! //! When defined, these rules get matched automatically in sequences (`~`) and repetitions //! (`*`, `+`) between expressions. Atomic rules and those rules called by atomic rules are exempt //! from this behavior. //! //! These rules should be defined so as to match one whitespace character and one comment only since //! they are run in repetitions. //! //! If both `WHITESPACE` and `COMMENT` are defined, this grammar: //! //! ```ignore //! a = { b ~ c } //! ``` //! //! is effectively transformed into this one behind the scenes: //! //! ```ignore //! a = { b ~ WHITESPACE* ~ (COMMENT ~ WHITESPACE*)* ~ c } //! ``` //! //! ## `PUSH`, `POP`, `DROP`, and `PEEK` //! //! `PUSH(e)` simply pushes the captured string of the expression `e` down a stack. This stack can //! then later be used to match grammar based on its content with `POP` and `PEEK`. //! //! `PEEK` always matches the string at the top of stack. So, if the stack contains `["b", "a"]` //! (`"a"` being on top), this grammar: //! //! ```ignore //! a = { PEEK } //! ``` //! //! is effectively transformed into at parse time: //! //! ```ignore //! a = { "a" } //! ``` //! //! `POP` works the same way with the exception that it pops the string off of the stack if the //! match worked. With the stack from above, if `POP` matches `"a"`, the stack will be mutated //! to `["b"]`. //! //! `DROP` makes it possible to remove the string at the top of the stack //! without matching it. If the stack is nonempty, `DROP` drops the top of the //! stack. If the stack is empty, then `DROP` fails to match. //! //! ### Advanced peeking //! //! `PEEK[start..end]` and `PEEK_ALL` allow to peek deeper into the stack. The syntax works exactly //! like Rust’s exclusive slice syntax. Additionally, negative indices can be used to indicate an //! offset from the top. If the end lies before or at the start, the expression matches (as does //! a `PEEK_ALL` on an empty stack). With the stack `["c", "b", "a"]` (`"a"` on top): //! //! ```ignore //! fill = PUSH("c") ~ PUSH("b") ~ PUSH("a") //! v = { PEEK_ALL } = { "a" ~ "b" ~ "c" } // top to bottom //! w = { PEEK[..] } = { "c" ~ "b" ~ "a" } // bottom to top //! x = { PEEK[1..2] } = { PEEK[1..-1] } = { "b" } //! y = { PEEK[..-2] } = { PEEK[0..1] } = { "a" } //! z = { PEEK[1..] } = { PEEK[-2..3] } = { "c" ~ "b" } //! n = { PEEK[2..-2] } = { PEEK[2..1] } = { "" } //! ``` //! //! For historical reasons, `PEEK_ALL` matches from top to bottom, while `PEEK[start..end]` matches //! from bottom to top. There is currently no syntax to match a slice of the stack top to bottom. //! //! ## `Rule` //! //! All rules defined or used in the grammar populate a generated `enum` called `Rule`. This //! implements `pest`'s `RuleType` and can be used throughout the API. //! //! ## `Built-in rules` //! //! Pest also comes with a number of built-in rules for convenience. They are: //! //! * `ASCII_DIGIT` - matches a numeric character from 0..9 //! * `ASCII_NONZERO_DIGIT` - matches a numeric character from 1..9 //! * `ASCII_BIN_DIGIT` - matches a numeric character from 0..1 //! * `ASCII_OCT_DIGIT` - matches a numeric character from 0..7 //! * `ASCII_HEX_DIGIT` - matches a numeric character from 0..9 or a..f or A..F //! * `ASCII_ALPHA_LOWER` - matches a character from a..z //! * `ASCII_ALPHA_UPPER` - matches a character from A..Z //! * `ASCII_ALPHA` - matches a character from a..z or A..Z //! * `ASCII_ALPHANUMERIC` - matches a character from a..z or A..Z or 0..9 //! * `ASCII` - matches a character from \x00..\x7f //! * `NEWLINE` - matches either "\n" or "\r\n" or "\r" #![doc(html_root_url = "https://docs.rs/pest_derive")] extern crate pest_generator; extern crate proc_macro; use proc_macro::TokenStream; #[proc_macro_derive(Parser, attributes(grammar, grammar_inline))] pub fn derive_parser(input: TokenStream) -> TokenStream { pest_generator::derive_parser(input.into(), true).into() }