add example app showing nfa OR dfa in rust

Author: chyyuu-tsinghua-cs

.gitignore

@@ -1,5 +1,6 @@
 *.iml
 dist/
+Cargo.lock
 target/
 .idea
 lex.yy.c

rust/show-nfa-dfa/Cargo.toml

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+[package]
+name = "showfa"
+version = "0.1.0"
+authors = ["Yu Chen <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+smallvec = "0.6.9"
+nom = "5.0"
+bitset = { git = "https://github.com/MashPlant/bitset" }
+re2dfa = { git = "https://github.com/MashPlant/re2dfa" }
+clap = "2.33.0"

rust/show-nfa-dfa/README.md

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+# Example
+convert a Regular Expression to NFA(Nondeterministic Finite Automata) to DFA(Deterministic Finite Automata) 
+
+## pre-requirement
+rust toolchain (nightly OR 1.39+) is installed.
+
+## usage
+tested on ubuntu 19.10 x86-64
+
+```
+# run the example with help
+cargo run -- -h
+
+# run the example for RE to NFA
+cargo run -- --nfa nfa.dot "(1|0)*1*0*10(1|0)*"
+
+# show the figure of NFA
+xdot nfa.dot
+
+# run the example for RE to NFA to raw DFA
+cargo run -- --raw_dfa raw_dfa.dot "(1|0)*1*0*10(1|0)*"
+
+# show the figure of raw DFA
+xdot raw_dfa.dot
+
+# run the example for RE to NFA to raw DFA to small DFA
+cargo run -- --dfa dfa.dot "(1|0)*1*0*10(1|0)*"
+
+# show the figure of small DFA
+xdot dfa.dot
+```

rust/show-nfa-dfa/src/main.rs

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+use re2dfa::*;
+use clap::{App, Arg};
+use std::{io, fs, process};
+
+fn main() -> io::Result<()> {
+  let m = App::new("show_fa")
+    .arg(Arg::with_name("input").required(true))
+    .arg(Arg::with_name("nfa").long("nfa").takes_value(true))
+    .arg(Arg::with_name("raw_dfa").long("raw_dfa").takes_value(true).help("show the dfa directly converted from nfa"))
+    .arg(Arg::with_name("dfa").long("dfa").takes_value(true).help("show the minimized dfa"))
+    .get_matches();
+  let input = m.value_of("input").unwrap();
+  let re = parse(input).unwrap_or_else(|e| {
+    eprintln!("Invalid regex `{}`: {}", input, e);
+    process::exit(1);
+  });
+  let nfa = Nfa::from_re(&re);
+  if let Some(path) = m.value_of("nfa") { fs::write(path, nfa.print_dot())?; }
+  let dfa = Dfa::from_nfa(&nfa, 0);
+  if let Some(path) = m.value_of("raw_dfa") { fs::write(path, dfa.print_dot())?; }
+  let dfa = dfa.minimize();
+  if let Some(path) = m.value_of("dfa") { fs::write(path, dfa.print_dot())?; }
+  Ok(())
+}