Add parser (and etc.) support for print statements.

src/syntax/ast.rs

@@ -3,12 +3,12 @@ use crate::syntax::token_stream::Location;
 #[derive(Debug, PartialEq)]
 pub struct Program {
     pub statements: Vec<Statement>,
-    pub result: Expression,
 }
 
 #[derive(Debug, PartialEq)]
 pub enum Statement {
     Binding(Location, String, Expression),
+    Print(Location, String),
     Expr(Location, Expression),
 }