Allow a bare expression that will be evaluated and echo'd to stdin

rust/src/main.rs

@@ -10,7 +10,7 @@ fn repl() {
         let mut line = String::new();
         io::stdin().read_line(&mut line).unwrap();
         let tree = parser::parse_stmt(&line);
-        println!("{:?}", tree);
+        println!("{:#?}", tree);
     }
 }
 

rust/src/parser.rs

@@ -3,6 +3,7 @@ pub enum Stmt {
     Assignment(String, Expr),
     Funcall(Expr),
     Conditional(Vec<Expr>, Option<Expr>),
+    ReplPrint(Expr),
 }
 
 #[derive(Debug,PartialEq,Clone)]
@@ -34,7 +35,8 @@ peg::parser! {
         pub rule stmt() -> Stmt
             = a:assignment() { a } /
             f:funcall() stop() { Stmt::Funcall(f) } /
-            c:conditional() { c }
+            c:conditional() { c } /
+            e:expr() stop() { Stmt::ReplPrint(e) }
         rule expr() -> Expr = precedence! {
             e1:(@) "+" _ e2:@ { Expr::Plus(Box::new(e1), Box::new(e2)) }
             e1:(@) "-" _ e2:@ { Expr::Minus(Box::new(e1), Box::new(e2)) }