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
use crate::combinator::trace;
use crate::error::{ErrMode, ErrorKind, ParserError};
use crate::stream::Stream;
use crate::*;

#[doc(inline)]
pub use crate::dispatch;

/// Helper trait for the [`alt()`] combinator.
///
/// This trait is implemented for tuples of up to 21 elements
pub trait Alt<I, O, E> {
    /// Tests each parser in the tuple and returns the result of the first one that succeeds
    fn choice(&mut self, input: &mut I) -> PResult<O, E>;
}

/// Pick the first successful parser
///
/// To stop on an error, rather than trying further cases, see
/// [`cut_err`][crate::combinator::cut_err] ([example][crate::_tutorial::chapter_6]).
///
/// For tight control over the error when no match is found, add a final case using [`fail`][crate::combinator::fail].
/// Alternatively, with a [custom error type][crate::_topic::error], it is possible to track all
/// errors or return the error of the parser that went the farthest in the input data.
///
/// When the alternative cases have unique prefixes, [`dispatch`] can offer better performance.
///
/// # Example
///
/// ```rust
/// # use winnow::{error::ErrMode, error::InputError,error::ErrorKind, error::Needed};
/// # use winnow::prelude::*;
/// use winnow::ascii::{alpha1, digit1};
/// use winnow::combinator::alt;
/// # fn main() {
/// fn parser(input: &str) -> IResult<&str, &str> {
///   alt((alpha1, digit1)).parse_peek(input)
/// };
///
/// // the first parser, alpha1, recognizes the input
/// assert_eq!(parser("abc"), Ok(("", "abc")));
///
/// // the first parser returns an error, so alt tries the second one
/// assert_eq!(parser("123456"), Ok(("", "123456")));
///
/// // both parsers failed, and with the default error type, alt will return the last error
/// assert_eq!(parser(" "), Err(ErrMode::Backtrack(InputError::new(" ", ErrorKind::Slice))));
/// # }
/// ```
#[doc(alias = "choice")]
pub fn alt<Input: Stream, Output, Error, Alternatives>(
    mut alternatives: Alternatives,
) -> impl Parser<Input, Output, Error>
where
    Alternatives: Alt<Input, Output, Error>,
    Error: ParserError<Input>,
{
    trace("alt", move |i: &mut Input| alternatives.choice(i))
}

/// Helper trait for the [`permutation()`] combinator.
///
/// This trait is implemented for tuples of up to 21 elements
pub trait Permutation<I, O, E> {
    /// Tries to apply all parsers in the tuple in various orders until all of them succeed
    fn permutation(&mut self, input: &mut I) -> PResult<O, E>;
}

/// Applies a list of parsers in any order.
///
/// Permutation will succeed if all of the child parsers succeeded.
/// It takes as argument a tuple of parsers, and returns a
/// tuple of the parser results.
///
/// To stop on an error, rather than trying further permutations, see
/// [`cut_err`][crate::combinator::cut_err] ([example][crate::_tutorial::chapter_6]).
///
/// # Example
///
/// ```rust
/// # use winnow::{error::ErrMode,error::{InputError, ErrorKind}, error::Needed};
/// # use winnow::prelude::*;
/// use winnow::ascii::{alpha1, digit1};
/// use winnow::combinator::permutation;
/// # fn main() {
/// fn parser(input: &str) -> IResult<&str, (&str, &str)> {
///   permutation((alpha1, digit1)).parse_peek(input)
/// }
///
/// // permutation recognizes alphabetic characters then digit
/// assert_eq!(parser("abc123"), Ok(("", ("abc", "123"))));
///
/// // but also in inverse order
/// assert_eq!(parser("123abc"), Ok(("", ("abc", "123"))));
///
/// // it will fail if one of the parsers failed
/// assert_eq!(parser("abc;"), Err(ErrMode::Backtrack(InputError::new(";", ErrorKind::Slice))));
/// # }
/// ```
///
/// The parsers are applied greedily: if there are multiple unapplied parsers
/// that could parse the next slice of input, the first one is used.
/// ```rust
/// # use winnow::{error::ErrMode, error::{InputError, ErrorKind}};
/// # use winnow::prelude::*;
/// use winnow::combinator::permutation;
/// use winnow::token::any;
///
/// fn parser(input: &str) -> IResult<&str, (char, char)> {
///   permutation((any, 'a')).parse_peek(input)
/// }
///
/// // any parses 'b', then char('a') parses 'a'
/// assert_eq!(parser("ba"), Ok(("", ('b', 'a'))));
///
/// // any parses 'a', then char('a') fails on 'b',
/// // even though char('a') followed by any would succeed
/// assert_eq!(parser("ab"), Err(ErrMode::Backtrack(InputError::new("b", ErrorKind::Tag))));
/// ```
///
pub fn permutation<I: Stream, O, E: ParserError<I>, List: Permutation<I, O, E>>(
    mut l: List,
) -> impl Parser<I, O, E> {
    trace("permutation", move |i: &mut I| l.permutation(i))
}

impl<const N: usize, I: Stream, O, E: ParserError<I>, P: Parser<I, O, E>> Alt<I, O, E> for [P; N] {
    fn choice(&mut self, input: &mut I) -> PResult<O, E> {
        let mut error: Option<E> = None;

        let start = input.checkpoint();
        for branch in self {
            input.reset(&start);
            match branch.parse_next(input) {
                Err(ErrMode::Backtrack(e)) => {
                    error = match error {
                        Some(error) => Some(error.or(e)),
                        None => Some(e),
                    };
                }
                res => return res,
            }
        }

        match error {
            Some(e) => Err(ErrMode::Backtrack(e.append(input, &start, ErrorKind::Alt))),
            None => Err(ErrMode::assert(input, "`alt` needs at least one parser")),
        }
    }
}

impl<I: Stream, O, E: ParserError<I>, P: Parser<I, O, E>> Alt<I, O, E> for &mut [P] {
    fn choice(&mut self, input: &mut I) -> PResult<O, E> {
        let mut error: Option<E> = None;

        let start = input.checkpoint();
        for branch in self.iter_mut() {
            input.reset(&start);
            match branch.parse_next(input) {
                Err(ErrMode::Backtrack(e)) => {
                    error = match error {
                        Some(error) => Some(error.or(e)),
                        None => Some(e),
                    };
                }
                res => return res,
            }
        }

        match error {
            Some(e) => Err(ErrMode::Backtrack(e.append(input, &start, ErrorKind::Alt))),
            None => Err(ErrMode::assert(input, "`alt` needs at least one parser")),
        }
    }
}

macro_rules! alt_trait(
  ($first:ident $second:ident $($id: ident)+) => (
    alt_trait!(__impl $first $second; $($id)+);
  );
  (__impl $($current:ident)*; $head:ident $($id: ident)+) => (
    alt_trait_impl!($($current)*);

    alt_trait!(__impl $($current)* $head; $($id)+);
  );
  (__impl $($current:ident)*; $head:ident) => (
    alt_trait_impl!($($current)*);
    alt_trait_impl!($($current)* $head);
  );
);

macro_rules! alt_trait_impl(
  ($($id:ident)+) => (
    impl<
      I: Stream, Output, Error: ParserError<I>,
      $($id: Parser<I, Output, Error>),+
    > Alt<I, Output, Error> for ( $($id),+ ) {

      fn choice(&mut self, input: &mut I) -> PResult<Output, Error> {
        let start = input.checkpoint();
        match self.0.parse_next(input) {
          Err(ErrMode::Backtrack(e)) => alt_trait_inner!(1, self, input, start, e, $($id)+),
          res => res,
        }
      }
    }
  );
);

macro_rules! succ (
  (0, $submac:ident ! ($($rest:tt)*)) => ($submac!(1, $($rest)*));
  (1, $submac:ident ! ($($rest:tt)*)) => ($submac!(2, $($rest)*));
  (2, $submac:ident ! ($($rest:tt)*)) => ($submac!(3, $($rest)*));
  (3, $submac:ident ! ($($rest:tt)*)) => ($submac!(4, $($rest)*));
  (4, $submac:ident ! ($($rest:tt)*)) => ($submac!(5, $($rest)*));
  (5, $submac:ident ! ($($rest:tt)*)) => ($submac!(6, $($rest)*));
  (6, $submac:ident ! ($($rest:tt)*)) => ($submac!(7, $($rest)*));
  (7, $submac:ident ! ($($rest:tt)*)) => ($submac!(8, $($rest)*));
  (8, $submac:ident ! ($($rest:tt)*)) => ($submac!(9, $($rest)*));
  (9, $submac:ident ! ($($rest:tt)*)) => ($submac!(10, $($rest)*));
  (10, $submac:ident ! ($($rest:tt)*)) => ($submac!(11, $($rest)*));
  (11, $submac:ident ! ($($rest:tt)*)) => ($submac!(12, $($rest)*));
  (12, $submac:ident ! ($($rest:tt)*)) => ($submac!(13, $($rest)*));
  (13, $submac:ident ! ($($rest:tt)*)) => ($submac!(14, $($rest)*));
  (14, $submac:ident ! ($($rest:tt)*)) => ($submac!(15, $($rest)*));
  (15, $submac:ident ! ($($rest:tt)*)) => ($submac!(16, $($rest)*));
  (16, $submac:ident ! ($($rest:tt)*)) => ($submac!(17, $($rest)*));
  (17, $submac:ident ! ($($rest:tt)*)) => ($submac!(18, $($rest)*));
  (18, $submac:ident ! ($($rest:tt)*)) => ($submac!(19, $($rest)*));
  (19, $submac:ident ! ($($rest:tt)*)) => ($submac!(20, $($rest)*));
  (20, $submac:ident ! ($($rest:tt)*)) => ($submac!(21, $($rest)*));
);

macro_rules! alt_trait_inner(
  ($it:tt, $self:expr, $input:expr, $start:ident, $err:expr, $head:ident $($id:ident)+) => ({
    $input.reset(&$start);
    match $self.$it.parse_next($input) {
      Err(ErrMode::Backtrack(e)) => {
        let err = $err.or(e);
        succ!($it, alt_trait_inner!($self, $input, $start, err, $($id)+))
      }
      res => res,
    }
  });
  ($it:tt, $self:expr, $input:expr, $start:ident, $err:expr, $head:ident) => ({
    Err(ErrMode::Backtrack($err.append($input, &$start, ErrorKind::Alt)))
  });
);

alt_trait!(Alt2 Alt3 Alt4 Alt5 Alt6 Alt7 Alt8 Alt9 Alt10 Alt11 Alt12 Alt13 Alt14 Alt15 Alt16 Alt17 Alt18 Alt19 Alt20 Alt21 Alt22);

// Manually implement Alt for (A,), the 1-tuple type
impl<I: Stream, O, E: ParserError<I>, A: Parser<I, O, E>> Alt<I, O, E> for (A,) {
    fn choice(&mut self, input: &mut I) -> PResult<O, E> {
        self.0.parse_next(input)
    }
}

macro_rules! permutation_trait(
  (
    $name1:ident $ty1:ident $item1:ident
    $name2:ident $ty2:ident $item2:ident
    $($name3:ident $ty3:ident $item3:ident)*
  ) => (
    permutation_trait!(__impl $name1 $ty1 $item1, $name2 $ty2 $item2; $($name3 $ty3 $item3)*);
  );
  (
    __impl $($name:ident $ty:ident $item:ident),+;
    $name1:ident $ty1:ident $item1:ident $($name2:ident $ty2:ident $item2:ident)*
  ) => (
    permutation_trait_impl!($($name $ty $item),+);
    permutation_trait!(__impl $($name $ty $item),+ , $name1 $ty1 $item1; $($name2 $ty2 $item2)*);
  );
  (__impl $($name:ident $ty:ident $item:ident),+;) => (
    permutation_trait_impl!($($name $ty $item),+);
  );
);

macro_rules! permutation_trait_impl(
  ($($name:ident $ty:ident $item:ident),+) => (
    impl<
      I: Stream, $($ty),+ , Error: ParserError<I>,
      $($name: Parser<I, $ty, Error>),+
    > Permutation<I, ( $($ty),+ ), Error> for ( $($name),+ ) {

      fn permutation(&mut self, input: &mut I) -> PResult<( $($ty),+ ), Error> {
        let mut res = ($(Option::<$ty>::None),+);

        loop {
          let mut err: Option<Error> = None;
          let start = input.checkpoint();
          permutation_trait_inner!(0, self, input, start, res, err, $($name)+);

          // If we reach here, every iterator has either been applied before,
          // or errored on the remaining input
          if let Some(err) = err {
            // There are remaining parsers, and all errored on the remaining input
            input.reset(&start);
            return Err(ErrMode::Backtrack(err.append(input, &start, ErrorKind::Alt)));
          }

          // All parsers were applied
          match res {
            ($(Some($item)),+) => return Ok(($($item),+)),
            _ => unreachable!(),
          }
        }
      }
    }
  );
);

macro_rules! permutation_trait_inner(
  ($it:tt, $self:expr, $input:ident, $start:ident, $res:expr, $err:expr, $head:ident $($id:ident)*) => (
    if $res.$it.is_none() {
      $input.reset(&$start);
      match $self.$it.parse_next($input) {
        Ok(o) => {
          $res.$it = Some(o);
          continue;
        }
        Err(ErrMode::Backtrack(e)) => {
          $err = Some(match $err {
            Some(err) => err.or(e),
            None => e,
          });
        }
        Err(e) => return Err(e),
      };
    }
    succ!($it, permutation_trait_inner!($self, $input, $start, $res, $err, $($id)*));
  );
  ($it:tt, $self:expr, $input:ident, $start:ident, $res:expr, $err:expr,) => ();
);

permutation_trait!(
  P1 O1 o1
  P2 O2 o2
  P3 O3 o3
  P4 O4 o4
  P5 O5 o5
  P6 O6 o6
  P7 O7 o7
  P8 O8 o8
  P9 O9 o9
  P10 O10 o10
  P11 O11 o11
  P12 O12 o12
  P13 O13 o13
  P14 O14 o14
  P15 O15 o15
  P16 O16 o16
  P17 O17 o17
  P18 O18 o18
  P19 O19 o19
  P20 O20 o20
  P21 O21 o21
);