Add TODO notes

Author: ax0

src/backends/mock_main.rs

@@ -408,6 +408,8 @@ impl MainPod for MockMainPod {
             .is_some();
         // check that all `input_statements` of type `ValueOf` with origin=SELF have unique keys
         // (no duplicates)
+        // TODO: Instead of doing this, do a uniqueness check when verifying the output of a
+        // `NewValue` operation.
         let value_ofs_unique = {
             let key_id_pairs = input_statements
                 .into_iter()

src/middleware.rs

@@ -377,6 +377,7 @@ impl ToFields for StatementArg {
     }
 }
 
+// TODO: Replace this with a more stringly typed enum as in the Devcon implementation.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Statement(pub NativeStatement, pub Vec<StatementArg>);
 
@@ -471,6 +472,7 @@ impl OperationArg {
     }
 }
 
+// TODO: Replace this with a more stringly typed enum as in the Devcon implementation.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Operation(pub NativeOperation, pub Vec<OperationArg>);
 
@@ -482,6 +484,7 @@ impl Operation {
         &self.1
     }
     // TODO: Argument checking.
+    // TODO: Use `Err` for all type mismatches rather than `false`.
     /// Checks the given operation against a statement.
     pub fn check(&self, output_statement: Statement) -> Result<bool> {
         use NativeOperation::*;