Add variable resolution; the error behavior is pretty bad here.

src/syntax/ast.rs

@@ -31,7 +31,6 @@ where
 pub enum Statement {
     Binding(Location, String, Expression),
     Print(Location, String),
-    Expr(Location, Expression),
 }
 
 impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Statement
@@ -51,7 +50,6 @@ where
                 .text("print")
                 .append(allocator.space())
                 .append(allocator.text(var.to_string())),
-            Statement::Expr(_, expr) => expr.pretty(allocator),
         }
     }
 }