Add ParserMatchesIterator

Author: ictrobot

crates/utils/src/parser/base.rs

@@ -3,7 +3,7 @@ use crate::parser::combinator::{
     Map, MapResult, Optional, Or, RepeatArrayVec, RepeatN, RepeatVec, WithPrefix, WithSuffix,
 };
 use crate::parser::error::{ParseError, WithErrorMsg};
-use crate::parser::iterator::ParserIterator;
+use crate::parser::iterator::{ParserIterator, ParserMatchesIterator};
 use crate::parser::simple::{Constant, Eol};
 use crate::parser::then::{Then, Then2, Unimplemented};
 
@@ -414,6 +414,29 @@ pub trait Parser: Sized {
             parser: self,
         }
     }
+
+    /// Create an iterator which returns matches only and skips over errors.
+    ///
+    /// This is intended for cases that require extracting matches out of the input.
+    /// Otherwise, [`parse_iterator`](Self::parse_iterator) should be used with a parser that can
+    /// match the entire input structure.
+    ///
+    /// # Examples
+    /// ```
+    /// # use utils::parser::{self, Parser};
+    /// assert_eq!(
+    ///     parser::u32()
+    ///         .matches_iterator("abc123d456efg7hi8jk9lmnop")
+    ///         .collect::<Vec<_>>(),
+    ///     vec![123, 456, 7, 8, 9]
+    /// );
+    /// ```
+    fn matches_iterator(self, input: &str) -> ParserMatchesIterator<Self> {
+        ParserMatchesIterator {
+            remaining: input.as_bytes(),
+            parser: self,
+        }
+    }
 }
 
 // Workaround to allow using methods which consume a parser in methods which take references.

crates/utils/src/parser/iterator.rs

@@ -36,3 +36,31 @@ impl<'a, P: Parser> Iterator for ParserIterator<'a, P> {
 }
 
 impl<P: Parser> FusedIterator for ParserIterator<'_, P> {}
+
+/// An iterator which returns successful parse outputs only, skipping over errors.
+///
+/// See [`Parser::matches_iterator`].
+#[derive(Copy, Clone)]
+#[must_use = "iterators are lazy and do nothing unless consumed"]
+pub struct ParserMatchesIterator<'a, P> {
+    pub(super) remaining: &'a [u8],
+    pub(super) parser: P,
+}
+
+impl<'a, P: Parser> Iterator for ParserMatchesIterator<'a, P> {
+    type Item = P::Output<'a>;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        while !self.remaining.is_empty() {
+            if let Ok((v, remaining)) = self.parser.parse(self.remaining) {
+                self.remaining = remaining;
+                return Some(v);
+            }
+            self.remaining = &self.remaining[1..];
+        }
+        None
+    }
+}
+
+impl<P: Parser> FusedIterator for ParserMatchesIterator<'_, P> {}

crates/utils/src/parser/mod.rs

@@ -12,7 +12,7 @@ mod then;
 
 pub use base::*;
 pub use error::ParseError;
-pub use iterator::ParserIterator;
+pub use iterator::{ParserIterator, ParserMatchesIterator};
 pub use number::{i128, i16, i32, i64, i8, number_range, u128, u16, u32, u64, u8};
 pub use one_of::one_of;
 pub use simple::{byte, byte_range, constant, eof, eol, noop, take_while, take_while1};

crates/year2024/src/day03.rs

@@ -7,32 +7,31 @@ pub struct Day03 {
     part2: u32,
 }
 
+enum Instruction {
+    Mul(u32, u32),
+    Do,
+    Dont,
+}
+
 impl Day03 {
     pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let matches = parser::parse_tree!(
+            ("mul(", a @ parser::u32(), ",", b @ parser::u32(), ")") => Instruction::Mul(a, b),
+            ("don't()") => Instruction::Dont,
+            ("do()") => Instruction::Do,
+        )
+        .matches_iterator(input);
+
         let (mut part1, mut part2) = (0, 0);
         let mut enabled = true;
-
-        let mut input = input.as_bytes();
-        while !input.is_empty() {
-            if let Ok(([a, b], remaining)) = parser::u32()
-                .repeat_n(b',')
-                .with_prefix("mul(")
-                .with_suffix(")")
-                .parse(input)
-            {
-                part1 += a * b;
-                if enabled {
-                    part2 += a * b;
+        for instruction in matches {
+            match instruction {
+                Instruction::Mul(a, b) => {
+                    part1 += a * b;
+                    part2 += if enabled { a * b } else { 0 };
                 }
-                input = remaining;
-            } else if let Some(remaining) = input.strip_prefix(b"do()") {
-                enabled = true;
-                input = remaining;
-            } else if let Some(remaining) = input.strip_prefix(b"don't()") {
-                enabled = false;
-                input = remaining;
-            } else {
-                input = &input[1..];
+                Instruction::Do => enabled = true,
+                Instruction::Dont => enabled = false,
             }
         }