1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
// pest. The Elegant Parser
// Copyright (c) 2018 Dragoș Tiselice
//
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. All files in the project carrying such notice may not be copied,
// modified, or distributed except according to those terms.
#![no_std]
#![doc(
    html_logo_url = "https://raw.githubusercontent.com/pest-parser/pest/master/pest-logo.svg",
    html_favicon_url = "https://raw.githubusercontent.com/pest-parser/pest/master/pest-logo.svg"
)]
#![warn(missing_docs, rust_2018_idioms, unused_qualifications)]
//! # 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]
//! * find previous common questions answered or ask questions on [GitHub Discussions]
//! * leave feedback, ask questions, or greet us on [Gitter] or [Discord]
//!
//! [book]: https://pest.rs/book
//! [docs.rs]: https://docs.rs/pest
//! [fiddle]: https://pest.rs/#editor
//! [Gitter]: https://gitter.im/pest-parser/pest
//! [Discord]: https://discord.gg/XEGACtWpT2
//! [GitHub Discussions]: https://github.com/pest-parser/pest/discussions
//!
//! ## Usage
//!
//! The core of pest is the trait [`Parser`], which provides an interface to the parsing
//! functionality.
//!
//! The accompanying crate `pest_derive` can automatically generate a [`Parser`] from a PEG
//! grammar. Using `pest_derive` is highly encouraged, but it is also possible to implement
//! [`Parser`] manually if required.
//!
//! ## `.pest` files
//!
//! Grammar definitions reside in custom `.pest` files located in the crate `src` directory.
//! Parsers are automatically generated from these files using `#[derive(Parser)]` and a special
//! `#[grammar = "..."]` attribute on a dummy struct.
//!
//! ```ignore
//! #[derive(Parser)]
//! #[grammar = "path/to/my_grammar.pest"] // relative to src
//! struct MyParser;
//! ```
//!
//! The syntax of `.pest` files is documented in the [`pest_derive` crate].
//!
//! ## Inline grammars
//!
//! Grammars can also be inlined by using the `#[grammar_inline = "..."]` attribute.
//!
//! [`Parser`]: trait.Parser.html
//! [`pest_derive` crate]: https://docs.rs/pest_derive/
//!
//! ## 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`                             |
//! | <code>e1 \| e2</code> | 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.
//!
//! Matching is greedy, without backtracking.  Note the difference in behavior for
//! these two rules in matching identifiers that don't end in an underscore:
//!
//! ```ignore
//! // input: ab_bb_b
//!
//! identifier = @{ "a" ~ ("b"|"_")* ~ "b" }
//! // matches:      a     b_bb_b       nothing -> error!      
//!
//! identifier = @{ "a" ~ ("_"* ~ "b")* }
//! // matches:      a     b, _bb, _b   in three repetitions
//! ```
//!
//! 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.
//! Many languages have "keyword" tokens (e.g. if, for, while) as well as general
//! tokens (e.g. identifier) that matches any word. In order to match a keyword,
//! generally, you may need to restrict that is not immediately followed by another
//! letter or digit (otherwise it would be matched as an identifier).
//!
//! ## 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")]

extern crate alloc;
#[cfg(feature = "std")]
extern crate std;

pub use crate::parser::Parser;
pub use crate::parser_state::{
    set_call_limit, set_error_detail, state, Atomicity, Lookahead, MatchDir, ParseResult,
    ParserState,
};
pub use crate::position::Position;
pub use crate::span::{merge_spans, Lines, LinesSpan, Span};
pub use crate::stack::Stack;
pub use crate::token::Token;
use core::fmt::Debug;
use core::hash::Hash;

pub mod error;
pub mod iterators;
mod macros;
mod parser;
mod parser_state;
mod position;
pub mod pratt_parser;
#[deprecated(
    since = "2.4.0",
    note = "Use `pest::pratt_parser` instead (it is an equivalent which also supports unary prefix/suffix operators).
While prec_climber is going to be kept in 2.x minor and patch releases, it may be removed in a future major release."
)]
pub mod prec_climber;
mod span;
mod stack;
mod token;

#[doc(hidden)]
pub mod unicode;

/// A trait which parser rules must implement.
///
/// This trait is set up so that any struct that implements all of its required traits will
/// automatically implement this trait as well.
///
/// This is essentially a [trait alias](https://github.com/rust-lang/rfcs/pull/1733). When trait
/// aliases are implemented, this may be replaced by one.
pub trait RuleType: Copy + Debug + Eq + Hash + Ord {}

impl<T: Copy + Debug + Eq + Hash + Ord> RuleType for T {}