libripgrep: initial commit introducing libripgrep

libripgrep is not any one library, but rather, a collection of libraries
that roughly separate the following key distinct phases in a grep
implementation:

  1. Pattern matching (e.g., by a regex engine).
  2. Searching a file using a pattern matcher.
  3. Printing results.

Ultimately, both (1) and (3) are defined by de-coupled interfaces, of
which there may be multiple implementations. Namely, (1) is satisfied by
the `Matcher` trait in the `grep-matcher` crate and (3) is satisfied by
the `Sink` trait in the `grep2` crate. The searcher (2) ties everything
together and finds results using a matcher and reports those results
using a `Sink` implementation.

grep-matcher/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "grep-matcher"
+version = "0.0.1"  #:version
+authors = ["Andrew Gallant <jamslam@gmail.com>"]
+description = """
+A trait for regular expressions, with a focus on line oriented search.
+"""
+documentation = "https://docs.rs/grep-matcher"
+homepage = "https://github.com/BurntSushi/ripgrep"
+repository = "https://github.com/BurntSushi/ripgrep"
+readme = "README.md"
+keywords = ["regex", "pattern", "trait"]
+license = "Unlicense/MIT"
+autotests = false
+
+[dependencies]
+memchr = "2"
+
+[dev-dependencies]
+regex = "1"
+
+[[test]]
+name = "integration"
+path = "tests/tests.rs"

grep-matcher/LICENSE-MIT

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Andrew Gallant
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

grep-matcher/README.md

@@ -0,0 +1,4 @@
+grep
+----
+This is a *library* that provides grep-style line-by-line regex searching (with
+comparable performance to `grep` itself).

grep-matcher/UNLICENSE

@@ -0,0 +1,24 @@
+This is free and unencumbered software released into the public domain.
+
+Anyone is free to copy, modify, publish, use, compile, sell, or
+distribute this software, either in source code form or as a compiled
+binary, for any purpose, commercial or non-commercial, and by any
+means.
+
+In jurisdictions that recognize copyright laws, the author or authors
+of this software dedicate any and all copyright interest in the
+software to the public domain. We make this dedication for the benefit
+of the public at large and to the detriment of our heirs and
+successors. We intend this dedication to be an overt act of
+relinquishment in perpetuity of all present and future rights to this
+software under copyright law.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
+
+For more information, please refer to <http://unlicense.org/>

grep-matcher/src/interpolate.rs

@@ -0,0 +1,328 @@
+use std::str;
+
+use memchr::memchr;
+
+/// Interpolate capture references in `replacement` and write the interpolation
+/// result to `dst`. References in `replacement` take the form of $N or $name,
+/// where `N` is a capture group index and `name` is a capture group name. The
+/// function provided, `name_to_index`, maps capture group names to indices.
+///
+/// The `append` function given is responsible for writing the replacement
+/// to the `dst` buffer. That is, it is called with the capture group index
+/// of a capture group reference and is expected to resolve the index to its
+/// corresponding matched text. If no such match exists, then `append` should
+/// not write anything to its given buffer.
+pub fn interpolate<A, N>(
+    mut replacement: &[u8],
+    mut append: A,
+    mut name_to_index: N,
+    dst: &mut Vec<u8>,
+) where
+    A: FnMut(usize, &mut Vec<u8>),
+    N: FnMut(&str) -> Option<usize>
+{
+    while !replacement.is_empty() {
+        match memchr(b'$', replacement) {
+            None => break,
+            Some(i) => {
+                dst.extend(&replacement[..i]);
+                replacement = &replacement[i..];
+            }
+        }
+        if replacement.get(1).map_or(false, |&b| b == b'$') {
+            dst.push(b'$');
+            replacement = &replacement[2..];
+            continue;
+        }
+        debug_assert!(!replacement.is_empty());
+        let cap_ref = match find_cap_ref(replacement) {
+            Some(cap_ref) => cap_ref,
+            None => {
+                dst.push(b'$');
+                replacement = &replacement[1..];
+                continue;
+            }
+        };
+        replacement = &replacement[cap_ref.end..];
+        match cap_ref.cap {
+            Ref::Number(i) => append(i, dst),
+            Ref::Named(name) => {
+                if let Some(i) = name_to_index(name) {
+                    append(i, dst);
+                }
+            }
+        }
+    }
+    dst.extend(replacement);
+}
+
+/// `CaptureRef` represents a reference to a capture group inside some text.
+/// The reference is either a capture group name or a number.
+///
+/// It is also tagged with the position in the text immediately proceding the
+/// capture reference.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+struct CaptureRef<'a> {
+    cap: Ref<'a>,
+    end: usize,
+}
+
+/// A reference to a capture group in some text.
+///
+/// e.g., `$2`, `$foo`, `${foo}`.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+enum Ref<'a> {
+    Named(&'a str),
+    Number(usize),
+}
+
+impl<'a> From<&'a str> for Ref<'a> {
+    fn from(x: &'a str) -> Ref<'a> {
+        Ref::Named(x)
+    }
+}
+
+impl From<usize> for Ref<'static> {
+    fn from(x: usize) -> Ref<'static> {
+        Ref::Number(x)
+    }
+}
+
+/// Parses a possible reference to a capture group name in the given text,
+/// starting at the beginning of `replacement`.
+///
+/// If no such valid reference could be found, None is returned.
+fn find_cap_ref(replacement: &[u8]) -> Option<CaptureRef> {
+    let mut i = 0;
+    if replacement.len() <= 1 || replacement[0] != b'$' {
+        return None;
+    }
+    let mut brace = false;
+    i += 1;
+    if replacement[i] == b'{' {
+        brace = true;
+        i += 1;
+    }
+    let mut cap_end = i;
+    while replacement.get(cap_end).map_or(false, is_valid_cap_letter) {
+        cap_end += 1;
+    }
+    if cap_end == i {
+        return None;
+    }
+    // We just verified that the range 0..cap_end is valid ASCII, so it must
+    // therefore be valid UTF-8. If we really cared, we could avoid this UTF-8
+    // check with an unchecked conversion or by parsing the number straight
+    // from &[u8].
+    let cap = str::from_utf8(&replacement[i..cap_end])
+        .expect("valid UTF-8 capture name");
+    if brace {
+        if !replacement.get(cap_end).map_or(false, |&b| b == b'}') {
+            return None;
+        }
+        cap_end += 1;
+    }
+    Some(CaptureRef {
+        cap: match cap.parse::<u32>() {
+            Ok(i) => Ref::Number(i as usize),
+            Err(_) => Ref::Named(cap),
+        },
+        end: cap_end,
+    })
+}
+
+/// Returns true if and only if the given byte is allowed in a capture name.
+fn is_valid_cap_letter(b: &u8) -> bool {
+    match *b {
+        b'0' ... b'9' | b'a' ... b'z' | b'A' ... b'Z' | b'_' => true,
+        _ => false,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{CaptureRef, find_cap_ref, interpolate};
+
+    macro_rules! find {
+        ($name:ident, $text:expr) => {
+            #[test]
+            fn $name() {
+                assert_eq!(None, find_cap_ref($text.as_bytes()));
+            }
+        };
+        ($name:ident, $text:expr, $capref:expr) => {
+            #[test]
+            fn $name() {
+                assert_eq!(Some($capref), find_cap_ref($text.as_bytes()));
+            }
+        };
+    }
+
+    macro_rules! c {
+        ($name_or_number:expr, $pos:expr) => {
+            CaptureRef { cap: $name_or_number.into(), end: $pos }
+        };
+    }
+
+    find!(find_cap_ref1, "$foo", c!("foo", 4));
+    find!(find_cap_ref2, "${foo}", c!("foo", 6));
+    find!(find_cap_ref3, "$0", c!(0, 2));
+    find!(find_cap_ref4, "$5", c!(5, 2));
+    find!(find_cap_ref5, "$10", c!(10, 3));
+    find!(find_cap_ref6, "$42a", c!("42a", 4));
+    find!(find_cap_ref7, "${42}a", c!(42, 5));
+    find!(find_cap_ref8, "${42");
+    find!(find_cap_ref9, "${42 ");
+    find!(find_cap_ref10, " $0 ");
+    find!(find_cap_ref11, "$");
+    find!(find_cap_ref12, " ");
+    find!(find_cap_ref13, "");
+
+    // A convenience routine for using interpolate's unwieldy but flexible API.
+    fn interpolate_string(
+        mut name_to_index: Vec<(&'static str, usize)>,
+        caps: Vec<&'static str>,
+        replacement: &str,
+    ) -> String {
+        name_to_index.sort_by_key(|x| x.0);
+
+        let mut dst = vec![];
+        interpolate(
+            replacement.as_bytes(),
+            |i, dst| {
+                if let Some(&s) = caps.get(i) {
+                    dst.extend(s.as_bytes());
+                }
+            },
+            |name| -> Option<usize> {
+                name_to_index
+                    .binary_search_by_key(&name, |x| x.0)
+                    .ok()
+                    .map(|i| name_to_index[i].1)
+            },
+            &mut dst,
+        );
+        String::from_utf8(dst).unwrap()
+    }
+
+    macro_rules! interp {
+        ($name:ident, $map:expr, $caps:expr, $hay:expr, $expected:expr $(,)*) => {
+            #[test]
+            fn $name() {
+                assert_eq!($expected, interpolate_string($map, $caps, $hay));
+            }
+        }
+    }
+
+    interp!(
+        interp1,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test $foo test",
+        "test xxx test",
+    );
+
+    interp!(
+        interp2,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test$footest",
+        "test",
+    );
+
+    interp!(
+        interp3,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test${foo}test",
+        "testxxxtest",
+    );
+
+    interp!(
+        interp4,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test$2test",
+        "test",
+    );
+
+    interp!(
+        interp5,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test${2}test",
+        "testxxxtest",
+    );
+
+    interp!(
+        interp6,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test $$foo test",
+        "test $foo test",
+    );
+
+    interp!(
+        interp7,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "test $foo",
+        "test xxx",
+    );
+
+    interp!(
+        interp8,
+        vec![("foo", 2)],
+        vec!["", "", "xxx"],
+        "$foo test",
+        "xxx test",
+    );
+
+    interp!(
+        interp9,
+        vec![("bar", 1), ("foo", 2)],
+        vec!["", "yyy", "xxx"],
+        "test $bar$foo",
+        "test yyyxxx",
+    );
+
+    interp!(
+        interp10,
+        vec![("bar", 1), ("foo", 2)],
+        vec!["", "yyy", "xxx"],
+        "test $ test",
+        "test $ test",
+    );
+
+    interp!(
+        interp11,
+        vec![("bar", 1), ("foo", 2)],
+        vec!["", "yyy", "xxx"],
+        "test ${} test",
+        "test ${} test",
+    );
+
+    interp!(
+        interp12,
+        vec![("bar", 1), ("foo", 2)],
+        vec!["", "yyy", "xxx"],
+        "test ${ } test",
+        "test ${ } test",
+    );
+
+    interp!(
+        interp13,
+        vec![("bar", 1), ("foo", 2)],
+        vec!["", "yyy", "xxx"],
+        "test ${a b} test",
+        "test ${a b} test",
+    );
+
+    interp!(
+        interp14,
+        vec![("bar", 1), ("foo", 2)],
+        vec!["", "yyy", "xxx"],
+        "test ${a} test",
+        "test  test",
+    );
+}

grep-matcher/tests/test_matcher.rs

@@ -0,0 +1,208 @@
+use grep_matcher::{Captures, Match, Matcher};
+use regex::bytes::Regex;
+
+use util::{RegexMatcher, RegexMatcherNoCaps};
+
+fn matcher(pattern: &str) -> RegexMatcher {
+    RegexMatcher::new(Regex::new(pattern).unwrap())
+}
+
+fn matcher_no_caps(pattern: &str) -> RegexMatcherNoCaps {
+    RegexMatcherNoCaps(Regex::new(pattern).unwrap())
+}
+
+fn m(start: usize, end: usize) -> Match {
+    Match::new(start, end)
+}
+
+#[test]
+fn find() {
+    let matcher = matcher(r"(\w+)\s+(\w+)");
+    assert_eq!(matcher.find(b" homer simpson ").unwrap(), Some(m(1, 14)));
+}
+
+#[test]
+fn find_iter() {
+    let matcher = matcher(r"(\w+)\s+(\w+)");
+    let mut matches = vec![];
+    matcher.find_iter(b"aa bb cc dd", |m| {
+        matches.push(m);
+        true
+    }).unwrap();
+    assert_eq!(matches, vec![m(0, 5), m(6, 11)]);
+
+    // Test that find_iter respects short circuiting.
+    matches.clear();
+    matcher.find_iter(b"aa bb cc dd", |m| {
+        matches.push(m);
+        false
+    }).unwrap();
+    assert_eq!(matches, vec![m(0, 5)]);
+}
+
+#[test]
+fn try_find_iter() {
+    #[derive(Clone, Debug, Eq, PartialEq)]
+    struct MyError;
+
+    let matcher = matcher(r"(\w+)\s+(\w+)");
+    let mut matches = vec![];
+    let err = matcher.try_find_iter(b"aa bb cc dd", |m| {
+        if matches.is_empty() {
+            matches.push(m);
+            Ok(true)
+        } else {
+            Err(MyError)
+        }
+    }).unwrap().unwrap_err();
+    assert_eq!(matches, vec![m(0, 5)]);
+    assert_eq!(err, MyError);
+}
+
+#[test]
+fn shortest_match() {
+    let matcher = matcher(r"a+");
+    // This tests that the default impl isn't doing anything smart, and simply
+    // defers to `find`.
+    assert_eq!(matcher.shortest_match(b"aaa").unwrap(), Some(3));
+    // The actual underlying regex is smarter.
+    assert_eq!(matcher.re.shortest_match(b"aaa"), Some(1));
+}
+
+#[test]
+fn captures() {
+    let matcher = matcher(r"(?P<a>\w+)\s+(?P<b>\w+)");
+    assert_eq!(matcher.capture_count(), 3);
+    assert_eq!(matcher.capture_index("a"), Some(1));
+    assert_eq!(matcher.capture_index("b"), Some(2));
+    assert_eq!(matcher.capture_index("nada"), None);
+
+    let mut caps = matcher.new_captures().unwrap();
+    assert!(matcher.captures(b" homer simpson ", &mut caps).unwrap());
+    assert_eq!(caps.get(0), Some(m(1, 14)));
+    assert_eq!(caps.get(1), Some(m(1, 6)));
+    assert_eq!(caps.get(2), Some(m(7, 14)));
+}
+
+#[test]
+fn captures_iter() {
+    let matcher = matcher(r"(?P<a>\w+)\s+(?P<b>\w+)");
+    let mut caps = matcher.new_captures().unwrap();
+    let mut matches = vec![];
+    matcher.captures_iter(b"aa bb cc dd", &mut caps, |caps| {
+        matches.push(caps.get(0).unwrap());
+        matches.push(caps.get(1).unwrap());
+        matches.push(caps.get(2).unwrap());
+        true
+    }).unwrap();
+    assert_eq!(matches, vec![
+        m(0, 5), m(0, 2), m(3, 5),
+        m(6, 11), m(6, 8), m(9, 11),
+    ]);
+
+    // Test that captures_iter respects short circuiting.
+    matches.clear();
+    matcher.captures_iter(b"aa bb cc dd", &mut caps, |caps| {
+        matches.push(caps.get(0).unwrap());
+        matches.push(caps.get(1).unwrap());
+        matches.push(caps.get(2).unwrap());
+        false
+    }).unwrap();
+    assert_eq!(matches, vec![
+        m(0, 5), m(0, 2), m(3, 5),
+    ]);
+}
+
+#[test]
+fn try_captures_iter() {
+    #[derive(Clone, Debug, Eq, PartialEq)]
+    struct MyError;
+
+    let matcher = matcher(r"(?P<a>\w+)\s+(?P<b>\w+)");
+    let mut caps = matcher.new_captures().unwrap();
+    let mut matches = vec![];
+    let err = matcher.try_captures_iter(b"aa bb cc dd", &mut caps, |caps| {
+        if matches.is_empty() {
+            matches.push(caps.get(0).unwrap());
+            matches.push(caps.get(1).unwrap());
+            matches.push(caps.get(2).unwrap());
+            Ok(true)
+        } else {
+            Err(MyError)
+        }
+    }).unwrap().unwrap_err();
+    assert_eq!(matches, vec![m(0, 5), m(0, 2), m(3, 5)]);
+    assert_eq!(err, MyError);
+}
+
+// Test that our default impls for capturing are correct. Namely, when
+// capturing isn't supported by the underlying matcher, then all of the
+// various capturing related APIs fail fast.
+#[test]
+fn no_captures() {
+    let matcher = matcher_no_caps(r"(?P<a>\w+)\s+(?P<b>\w+)");
+    assert_eq!(matcher.capture_count(), 0);
+    assert_eq!(matcher.capture_index("a"), None);
+    assert_eq!(matcher.capture_index("b"), None);
+    assert_eq!(matcher.capture_index("nada"), None);
+
+    let mut caps = matcher.new_captures().unwrap();
+    assert!(!matcher.captures(b"homer simpson", &mut caps).unwrap());
+
+    let mut called = false;
+    matcher.captures_iter(b"homer simpson", &mut caps, |_| {
+        called = true;
+        true
+    }).unwrap();
+    assert!(!called);
+}
+
+#[test]
+fn replace() {
+    let matcher = matcher(r"(\w+)\s+(\w+)");
+    let mut dst = vec![];
+    matcher.replace(b"aa bb cc dd", &mut dst, |_, dst| {
+        dst.push(b'z');
+        true
+    }).unwrap();
+    assert_eq!(dst, b"z z");
+
+    // Test that replacements respect short circuiting.
+    dst.clear();
+    matcher.replace(b"aa bb cc dd", &mut dst, |_, dst| {
+        dst.push(b'z');
+        false
+    }).unwrap();
+    assert_eq!(dst, b"z cc dd");
+}
+
+#[test]
+fn replace_with_captures() {
+    let matcher = matcher(r"(\w+)\s+(\w+)");
+    let haystack = b"aa bb cc dd";
+    let mut caps = matcher.new_captures().unwrap();
+    let mut dst = vec![];
+    matcher.replace_with_captures(haystack, &mut caps, &mut dst, |caps, dst| {
+        caps.interpolate(
+            |name| matcher.capture_index(name),
+            haystack,
+            b"$2 $1",
+            dst,
+        );
+        true
+    }).unwrap();
+    assert_eq!(dst, b"bb aa dd cc");
+
+    // Test that replacements respect short circuiting.
+    dst.clear();
+    matcher.replace_with_captures(haystack, &mut caps, &mut dst, |caps, dst| {
+        caps.interpolate(
+            |name| matcher.capture_index(name),
+            haystack,
+            b"$2 $1",
+            dst,
+        );
+        false
+    }).unwrap();
+    assert_eq!(dst, b"bb aa cc dd");
+}

grep-matcher/tests/tests.rs

@@ -0,0 +1,6 @@
+extern crate grep_matcher;
+extern crate regex;
+
+mod util;
+
+mod test_matcher;

grep-matcher/tests/util.rs

@@ -0,0 +1,104 @@
+use std::collections::HashMap;
+use std::result;
+
+use grep_matcher::{Captures, Match, Matcher, NoCaptures, NoError};
+use regex::bytes::{CaptureLocations, Regex};
+
+#[derive(Debug)]
+pub struct RegexMatcher {
+    pub re: Regex,
+    pub names: HashMap<String, usize>,
+}
+
+impl RegexMatcher {
+    pub fn new(re: Regex) -> RegexMatcher {
+        let mut names = HashMap::new();
+        for (i, optional_name) in re.capture_names().enumerate() {
+            if let Some(name) = optional_name {
+                names.insert(name.to_string(), i);
+            }
+        }
+        RegexMatcher {
+            re: re,
+            names: names,
+        }
+    }
+}
+
+type Result<T> = result::Result<T, NoError>;
+
+impl Matcher for RegexMatcher {
+    type Captures = RegexCaptures;
+    type Error = NoError;
+
+    fn find_at(
+        &self,
+        haystack: &[u8],
+        at: usize,
+    ) -> Result<Option<Match>> {
+        Ok(self.re
+            .find_at(haystack, at)
+            .map(|m| Match::new(m.start(), m.end())))
+    }
+
+    fn new_captures(&self) -> Result<RegexCaptures> {
+        Ok(RegexCaptures(self.re.capture_locations()))
+    }
+
+    fn captures_at(
+        &self,
+        haystack: &[u8],
+        at: usize,
+        caps: &mut RegexCaptures,
+    ) -> Result<bool> {
+        Ok(self.re.captures_read_at(&mut caps.0, haystack, at).is_some())
+    }
+
+    fn capture_count(&self) -> usize {
+        self.re.captures_len()
+    }
+
+    fn capture_index(&self, name: &str) -> Option<usize> {
+        self.names.get(name).map(|i| *i)
+    }
+
+    // We purposely don't implement any other methods, so that we test the
+    // default impls. The "real" Regex impl for Matcher provides a few more
+    // impls. e.g., Its `find_iter` impl is faster than what we can do here,
+    // since the regex crate avoids synchronization overhead.
+}
+
+#[derive(Debug)]
+pub struct RegexMatcherNoCaps(pub Regex);
+
+impl Matcher for RegexMatcherNoCaps {
+    type Captures = NoCaptures;
+    type Error = NoError;
+
+    fn find_at(
+        &self,
+        haystack: &[u8],
+        at: usize,
+    ) -> Result<Option<Match>> {
+        Ok(self.0
+            .find_at(haystack, at)
+            .map(|m| Match::new(m.start(), m.end())))
+    }
+
+    fn new_captures(&self) -> Result<NoCaptures> {
+        Ok(NoCaptures::new())
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct RegexCaptures(CaptureLocations);
+
+impl Captures for RegexCaptures {
+    fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    fn get(&self, i: usize) -> Option<Match> {
+        self.0.pos(i).map(|(s, e)| Match::new(s, e))
+    }
+}