Start working on bnf()

src/bnf.rs

@@ -1 +1,4 @@
-pub struct Bnf {}
+#[derive(Debug, Clone)]
+pub enum Bnf {
+    Production,
+}

src/parser.rs

@@ -147,6 +147,10 @@ impl<'a, I: ParserInput, O, E> Parser<I, O, E> for BoxedParser<'a, I, O, E> {
     fn parse(&self, input: I) -> ParseResult<I, O, E> {
         self.inner.parse(input)
     }
+
+    fn bnf(&self) -> Option<Bnf> {
+        self.inner.bnf()
+    }
 }
 
 impl<I: ParserInput, O, E, F> Parser<I, O, E> for F
@@ -158,6 +162,19 @@ where
     }
 }
 
+impl<I: ParserInput, O, E, F> Parser<I, O, E> for (F, Bnf)
+where
+    F: Fn(I) -> ParseResult<I, O, E>,
+{
+    fn parse(&self, input: I) -> ParseResult<I, O, E> {
+        self.0(input)
+    }
+
+    fn bnf(&self) -> Option<Bnf> {
+        Some(self.1.clone())
+    }
+}
+
 impl<I, O, E, T> Parser<I, O, E> for Rc<T>
 where
     I: ParserInput,
@@ -166,4 +183,8 @@ where
     fn parse(&self, input: I) -> ParseResult<I, O, E> {
         self.as_ref().parse(input)
     }
+
+    fn bnf(&self) -> Option<Bnf> {
+        self.as_ref().bnf()
+    }
 }