asserteq!( parseinput("4x23x21\n22x29x19").unwrap(), vec![(4, 23, 21), (22, 29, 19)] ); ```

Patterns

The argument you need to pass to the parser! macro is a pattern; all aoc-parse does is match strings against your chosen pattern and convert them into Rust values.

Here are some examples of patterns:

```rust lines(i32) // matches a list of integers, one per line // converts them to a Vec

line(lower+) // matches a single line of one or more lowercase letters // converts them to a Vec

lines({ // matches lines made up of the characters < = > "<" => -1, // converts them to a Vec> filled with -1, 0, and 1 "=" => 0, ">" => 1 }+) ```

Here are the pieces that you can use in a pattern:

• i8, i16, i32, i64, i128, isize - These match an integer, written out using decimal digits, with an optional + or - sign at the start, like 0 or -11474.

  It's an error if the string contains a number too big to fit in the type you chose. For example, parser!(i8).parse("1000") is an error. (It matches the string, but fails during the "convert" phase.)

• u8, u16, u32, u64, u128, usize - The same, but without the sign.

• i8_bin, i16_bin, i32_bin, i64_bin, i128_bin, isize_bin, u8_bin, u16_bin, u32_bin, u64_bin, u128_bin, usize_bin, i8_hex, i16_hex, i32_hex, i64_hex, i128_hex, isize_hex, u8_hex, u16_hex, u32_hex, u64_hex, u128_hex, usize_hex - Match an integer in base 2 or base 16. The _hex parsers allow both uppercase and lowercase digits A-F.

• bool - Matches either true or false and converts it to the corresponding bool value.

• alpha, alnum, upper, lower - Match single characters of various categories. (These use the Unicode categories, even though Advent of Code historically sticks to ASCII.)

• digit, digit_bin, digit_hex - Match a single ASCII character that's a digit in base 10, base 2, or base 16, respectively. The digit is converted to its numeric value, as a usize.

• any_char: Match the next character, no matter what it is (like . in a regular expression, except that any_char matches newline characters).

• 'x' or "hello" - A Rust character or string, in quotes, is a pattern that matches that exact text only.

  Exact patterns don't produce a value.

• pattern1 pattern2 pattern3... - Patterns can be concatenated to form larger patterns. This is how parser!(u64 "x" u64 "x" u64) matches the string 4x23x21. It simply matches each subpattern in order. It converts the match to a tuple if there are two or more subpatterns that produce values.

• parser_var - You can use previously defined parsers that you've stored in local variables.

  For example, the amount parser below makes use of the fraction parser defined on the previous line.

  ``` let fraction = parser!(i64 "/" u64); let amount = parser!(fraction " tsp");

  assert_eq!(amount.parse("1/4 tsp").unwrap(), (1, 4)); ```

  An identifier can also refer to a string or character constant.

• string(pattern) - Matches the given pattern, but instead of converting it to some value, simply return the matched characters as a String.

  By default, alpha+ returns a Vec<char>, and sometimes that is handy in AoC, but often it's better to have it return a String.

Repeating patterns:

• pattern* - Any pattern followed by an asterisk matches that pattern zero or more times. It converts the results to a Vec. For example, parser!("A"*) matches the strings A, AA, AAAAAAAAAAAAAA, and so on, as well as the empty string.

• pattern+ - Matches the pattern one or more times, producing a Vec. parser!("A"+) matches A, AA, etc., but not the empty string.

• pattern? - Optional pattern, producing a Rust Option. For example, parser!("x=" i32?) matches x=123, producing Some(123); it also matches x=, producing the value None.

  These behave just like the *, +, and ? special characters in regular expressions.

• repeat_sep(pattern, separator) - Match the given pattern any number of times, separated by the separator. This converts only the bits that match pattern to Rust values, producing a Vec. Any parts of the string matched by separator are not converted.

Custom conversion:

• ... name1:pattern1 ... => expr - On successfully matching the patterns to the left of =>, evaluate the Rust expression expr to convert the results to a single Rust value.

  Use this to convert input to structs. For instance, suppose your puzzle input contains each elf's name and height:

  text Holly=33 Ivy=7 DouglasFir=1093

  and you'd like to turn this into a vector of struct Elf values. The code you need is:

  ``` struct Elf { name: String, height: u32, }

  let p = parser!(lines( elf:string(alpha+) '=' ht:u32 => Elf { name: elf, height: ht } )); ```

  The name elf applies to the pattern string(alpha+) and the name ht applies to the pattern i32. The bit after the => is plain old Rust code.

  The names are in scope only for the following expr in the same set of matching parentheses or braces.

Alternatives:

• {pattern1, pattern2, ...} - Matches any one of the patterns. First try matching pattern1; if it matches, stop. If not, try pattern2, and so on. All the patterns must produce the same type of Rust value.

  This is sort of like a Rust match expression.

  For example, parser!({"<" => -1, ">" => 1}) either matches <, returning the value -1, or matches >, returing 1.

  Alternatives are handy when you want to convert the input into an enum. For example, my puzzle input for December 23, 2015 was a list of instructions that looked (in part) like this:

  text jie a, +4 tpl a inc a jmp +2 hlf a jmp -7

  This can be easily parsed into a vector of beautiful enums, like so:

  ``` enum Reg { A, B, }

  enum Insn { Hlf(Reg), Tpl(Reg), Inc(Reg), Jmp(isize), Jie(Reg, isize), Jio(Reg, isize), }

  use Reg::; use Insn::;

  let reg = parser!({"a" => A, "b" => B}); let p = parser!(lines({ "hlf " r:reg => Hlf(r), "tpl " r:reg => Tpl(r), "inc " r:reg => Inc(r), "jmp " offset:isize => Jmp(offset), "jie " r:reg ", " offset:isize => Jie(r, offset), "jio " r:reg ", " offset:isize => Jio(r, offset), })); ```

Lines and sections:

• line(pattern) - Matches a single line of text that matches pattern, and the newline at the end of the line.

  This is like ^pattern\n in regular expressions, with two minor differences:

  • line(pattern) will only ever match exactly one line of text, even if pattern could match more newlines.

  • If your input does not end with a newline, line() can still match the non-newline-terminated "line" at the end.

  line(string(any_char+)) matches a line of text, strips off the newline character, and returns the rest as a String.

  line("") matches a blank line.

• lines(pattern) - Matches any number of lines of text matching pattern. Each line must be terminated by a newline, '\n'.

  Equivalent to line(pattern)*.

  let p = parser!(lines(repeat_sep(digit, " "))); assert_eq!( p.parse("1 2 3\n4 5 6\n").unwrap(), vec![vec![1, 2, 3], vec![4, 5, 6]], );

• section(pattern) - Matches zero or more nonblank lines, followed by either a blank line or the end of input. The nonblank lines must match pattern.

  section() consumes the blank line. pattern should not expect to see it.

  It's common for an AoC puzzle input to have several lines of data, then a blank line, and then a different kind of data. You can parse this with section(p1) section(p2).

  section(lines(u64)) matches a section that's a list of numbers, one per line.

• sections(pattern) - Matches any number of sections matching pattern. Equivalent to section(pattern)*

  Bringing it all together to parse a complex example:

  ``` let example = "\ Wiring Diagram #1: a->q->E->z->J D->f->D

  Wiring Diagram #2: g->r->f g->B ";

  let p = parser!(sections( line("Wiring Diagram #" usize ":") lines(repeatsep(alpha, "->")) )); asserteq!( p.parse(example).unwrap(), vec![ (1, vec![vec!['a', 'q', 'E', 'z', 'J'], vec!['D', 'f', 'D']]), (2, vec![vec!['g', 'r', 'f'], vec!['g', 'B']]), ], ); ```

License: MIT