Add patched regex-automata

Cargo.toml

@@ -4,3 +4,8 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+anyhow = "1.0.86"
+regex-automata = "0.4.7"
+
+[patch.crates-io]
+regex-automata = { git = 'https://github.com/f-forcher/regex', branch = 'expose-state-iter' }

src/main.rs

@@ -1,3 +1,34 @@
-fn main() {
-    println!("Hello, world!");
+use anyhow::Result;
+use regex_automata::{
+    dfa::{dense, Automaton},
+    Anchored, Input,
+};
+
+fn main() -> Result<()> {
+    let dfa = dense::DFA::new(r"[0-9]*\.?[0-9]*")?;
+    let haystack = "1.34";
+
+    // The start state is determined by inspecting the position and the
+    // initial bytes of the haystack.
+    let mut state = dfa.start_state_forward(&Input::new(haystack).anchored(Anchored::Yes))?;
+    // Walk all the bytes in the haystack.
+    for &b in haystack.as_bytes().iter() {
+        state = dfa.next_state(state, b);
+    }
+
+    let states_num = dfa.tt.len();
+
+    println!("There are {} states in this dfa", states_num);
+
+    let states_ids: Vec<_> = dfa.tt.states().map(|state| state.id()).collect();
+
+    println!("Their IDs are {:?}", states_ids);
+
+    // DFAs in this crate require an explicit
+    // end-of-input transition if a search reaches
+    // the end of a haystack.
+    state = dfa.next_eoi_state(state);
+    assert!(dfa.is_match_state(state));
+
+    Ok(())
 }