test

.gitignore

@@ -0,0 +1 @@
+/target

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "aut"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/main.rs

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+#[derive(Debug,Clone)]
+enum RegExp {
+    Char(char),
+    Empt,
+    Epsilon,
+    Union(Box<RegExp>, Box<RegExp>),
+    Concat(Box<RegExp>, Box<RegExp>),
+    Kleene(Box<RegExp>),
+}
+
+fn is_nullable (r : &RegExp) -> bool {
+    match r {
+        RegExp::Epsilon => true,
+        RegExp::Kleene(_) => true,
+        RegExp::Union(r1, r2) => is_nullable(&*r1) | is_nullable(&*r2),
+        RegExp::Concat(r1, r2) => is_nullable(&*r1) & is_nullable(&*r2),
+        _ => false,
+    }
+}
+
+fn derivative(r : &RegExp, a : char) -> RegExp {
+    match r {
+        RegExp::Empt => RegExp::Empt,
+        RegExp::Epsilon => RegExp::Empt,
+        RegExp::Char(c) => if *c == a {
+            RegExp::Epsilon
+        } else { RegExp::Empt },
+        RegExp::Union(r1, r2) =>
+            RegExp::Union(Box::new(derivative(&*r1, a)), Box::new(derivative(&*r2, a))),
+        RegExp::Kleene(r) =>
+            RegExp::Concat(Box::new(derivative(&*r, a)),
+                           Box::new(RegExp::Kleene(Box::new(*r.clone())))),
+        RegExp::Concat(r1, r2) => {
+            let r : RegExp = RegExp::Concat(Box::new(derivative(&*r1, a)),
+                                            Box::new(*r2.clone()));
+            if is_nullable(&*r1) {
+                RegExp::Union(Box::new(derivative(&*r2, a)), Box::new(r))
+            } else {
+                r
+            }
+        }
+        _ => RegExp::Empt,
+    }
+}
+
+fn regexp_match(r : RegExp, s : &String) -> bool {
+    let chrs = s.chars();
+    let mut rs : RegExp = r;
+    for c in chrs {
+        println!("Computing der({:?}, {:?}) ...", rs, c);
+        rs = derivative(&rs, c); 
+    }
+    println!("Result: {:?}", rs);
+    is_nullable(&rs)
+}
+
+fn main() {
+    let r1 = RegExp::Concat(Box::new( RegExp::Char('a')), Box::new( RegExp::Char('b')));
+    let r2 = RegExp::Kleene(Box::new(r1.clone()));
+    let r3 = RegExp::Concat(Box::new(RegExp::Union(Box::new(r1.clone()), Box::new(RegExp::Char('c')))), Box::new(r2.clone()));
+    let inp = String::from("c");
+    let res = regexp_match(r3.clone(), &inp);
+    println!("match {:?}, {:?} = {:?}", r3, inp, res);
+}