gistfile1.rs

#![feature(collections)]
#![feature(box_patterns)]

#[derive(Clone, Debug)]
enum Regex {
    Term(RegexTerm),
    Or(RegexTerm, Box<Regex>),
}

impl Regex {
    pub fn matches<F: Fn(&str) -> bool>(&self, target : &str, matches_rest : &F) -> bool {
        match self {
            &Term(ref term) => term.matches(target, matches_rest),
            &Or(ref term, box ref r) =>
                term.matches(target, matches_rest) || r.matches(target, matches_rest),
        }
    }
}

#[derive(Clone, Debug)]
enum RegexTerm {
    Empty,
    Cons(RegexFactor, Box<RegexTerm>),
}

impl RegexTerm {
    pub fn matches<F: Fn(&str) -> bool>(&self, target : &str, matches_rest : &F) -> bool {
        match self {
            &Empty => matches_rest(target),
            &Cons(ref factor, box ref term) => {
                factor.matches(target, &|rest| {
                    term.matches(rest, matches_rest)
                })
            }
        }
    }
}

#[derive(Clone, Debug)]
enum RegexFactor {
    Star(RegexBase),
    Plus(RegexBase),
    Once(RegexBase),
}

impl RegexFactor {
    pub fn matches<F: Fn(&str) -> bool>(&self, target : &str, matches_rest : &F) -> bool {
        match self {
            &Star(ref base) => {
                // b*rest == bb*rest|rest
                matches_rest(target) || 
                    base.matches(target, &|rest| {
                        Star(base.clone()).matches(rest, matches_rest)
                    })
            },
            &Plus(ref base) => {
                // b+ == bb*
                base.matches(target, &|rest| {
                    Star(base.clone()).matches(rest, matches_rest)
                })
            },
            &Once(ref base) => base.matches(target, matches_rest),
        }
    }
}

#[derive(Clone, Debug)]
enum RegexBase {
    Paren(Box<Regex>),
    Char(char),
    Any(String),
    Dot,
}

impl RegexBase {
    pub fn matches<F: Fn(&str) -> bool>(&self, target : &str, matches_rest : &F) -> bool {
        match (self, target.slice_shift_char()) {
            (&Paren(box ref regex), _) =>
             regex.matches(target, matches_rest),
            (&Char(c), Some((tc, rest))) if tc == c => matches_rest(rest),
            (&Any(ref chars), Some((tc, rest)))
                if chars.contains_char(tc) => matches_rest(rest),
            (&Dot, Some((_, rest))) => matches_rest(rest),
            _ => false
        }
    }
}

use Regex::{Term, Or};
use RegexTerm::{Empty, Cons};
use RegexFactor::{Star, Plus, Once};
use RegexBase::{Char, Dot, Any, Paren};

fn parse_regex(regex : &str) -> (Regex, &str) {
    let (term, rest) = parse_term(regex);
    if rest.len() > 0 && rest.char_at(0) == '|' {
        let (r, rest2) = parse_regex(&rest[0..]);
        (Or(term, Box::new(r)), rest2)
    } else if rest.len() > 0 {
        panic!("Malformed regex {}", rest)
    } else {
        (Term(term), rest)
    }
}

fn parse_term(term : &str) -> (RegexTerm, &str) {
    if term.len() == 0 {
        (Empty, "")
    } else {
        let (factor, rest) = parse_factor(term);
        let (term, rest2) = parse_term(rest);
        (Cons(factor, Box::new(term)), rest2)
    }
}

fn parse_factor(factor : &str) -> (RegexFactor, &str)  {
    let (base, rest) = parse_base(factor);
    match rest.slice_shift_char() {
        Some(('*', _)) => (Star(base), &rest[1..]),
        Some(('+', _)) => (Plus(base), &rest[1..]),
        _ => (Once(base), rest),
    }
}

fn parse_base(factor : &str) -> (RegexBase, &str)  {
    match factor.slice_shift_char() {
        Some(('.', rest)) => {
            (Dot, rest)
        },
        Some(('[', rest)) => {
            let ind = rest.find(']').expect("Mismatched '['");
            (Any(String::from_str(&rest[..ind])), &rest[ind+1..])
        },
        Some(('(', rest)) => {
            let (x, r) = parse_regex(rest);
            (Paren(Box::new(x)), r)
        },
        Some((c, rest)) => {
            (Char(c), rest)
        },
        None => panic!("Malformed regex... parsing empty as base"),
    }
}

pub fn matches(regex : &str], target : &str) -> bool {
    let (regex, rest) = parse_regex(regex);
    if rest != "" {
        panic!("Malformed regex {:?}", regex)
    }
    regex.matches(target, &(|rest| rest.len() == 0))
}

#[test]
fn test_matches() {
    assert!(matches("asdf", "asdf"));
    assert!(!matches("asdf", "asdfg"));
    assert!(!matches("asdf", ""));
    assert!(!matches("asdf", "foo"));
    assert!(!matches("b", "a"));

    assert!(matches(".", "f"));
    assert!(matches(".", "a"));
    assert!(matches(".", "a"));

    assert!(matches(".*", ""));
    assert!(matches(".*", "anything"));
    assert!(matches("a*", "aaa"));
    assert!(matches("a*", "aaaaaa"));
    assert!(matches("a*", "a"));
    assert!(matches("a*", ""));
    assert!(matches("b*", "bbbb"));
    assert!(matches("aab*", "aabbbb"));
    assert!(matches("aab*", "aa"));

    assert!(matches(".*@.*", "trey@jellolabs.com"));
    assert!(matches(".*@.*", "@"));

    assert!(matches("a.c", "abc"));
    assert!(matches("a.c", "a1c"));
    assert!(!matches("a.c", "ac"));

    assert!(matches("a*a", "a"));
    assert!(matches("a*a", "aa"));
    assert!(matches("a*a", "aaaaaaa"));
    assert!(!matches("a*a", ""));

    assert!(matches(".*abc.*", "ababc"));
    assert!(matches(".*abc.*", "111abc222"));
    assert!(matches(".*abc.*", "abcab"));
}

#[test]
#[cfg(feature = "parsed")]
fn test_extended_features() {
    assert!(matches("[abc]", "a"));
    assert!(matches("[abc]", "b"));
    assert!(matches("[abc]*", "baccab"));

    assert!(matches("[abc]+", "baccab"));
    assert!(!matches("[abc]+", ""));
    assert!(matches("[abc]+xx", "abaxx"));

    assert!(matches("(abc)+", "abc"));
    assert!(matches("(abc)+", "abcabc"));
    assert!(matches("(ab+c)+", "abbbbcabbc"));

    assert!(matches("abc|d", "abc"));
    assert!(matches("abc|d", "d"));
    assert!(matches("(a*|d)e", "de"));
    assert!(matches("(a*|d)e", "aaae"));
    assert!(!matches("(a*|d)e", "aaade"));
    assert!(!matches("(a*|d)e", "aaa"));
}