ebnf

Chapter09/Cargo.toml

@@ -87,3 +87,7 @@ path = "debugging_assert.rs"
 [[bin]]
 name = "metaprogramming_grammar"
 path = "metaprogramming_grammar.rs"
+
+[[bin]]
+name = "metaprogramming_ebnf"
+path = "metaprogramming_ebnf.rs"

Chapter09/metaprogramming_ebnf.rs

@@ -0,0 +1,26 @@
+//this is a grammar sequence
+macro_rules! abc {
+  (a b c) => { println!("'a b c' is the only correct syntax.") };
+}
+
+//this is a grammar alternative
+macro_rules! a_or_b {
+  (a) => { println!("'a' is one correct syntax.") };
+  (b) => { println!("'b' is also correct syntax.") };
+}
+
+//this is a grammar alternative
+macro_rules! abc_or_aaa {
+  (a b c) => { println!("'a b c' is one correct syntax.") };
+  (a a a) => { println!("'a a a' is also correct syntax.") };
+}
+
+fn main() {
+   abc!(a b c);
+
+   a_or_b!(a);
+   a_or_b!(b);
+
+   abc_or_aaa!(a b c);
+   abc_or_aaa!(a a a);
+}