wip: fix(dsl): maybe getting somewhere?

core/src/lib.rs

@@ -46,9 +46,9 @@ pub trait MaybeHas<T>: Send + Sync {
 /// May compute a `RetVal` from `Args`.
 pub trait Eval<Args, RetVal> {
     /// A custom operation on [Args] that may return [Result::Err] or [Option::None].
-    fn try_eval (&self, args: Args) -> Perhaps<RetVal>;
+    fn try_eval (&self, args: &Args) -> Perhaps<RetVal>;
     /// Invoke a custom operation, converting a `None` result to a custom `Box<dyn Error>`.
-    fn eval <E: Into<Box<dyn std::error::Error>>> (&self, args: Args, error: impl Fn()->E)
+    fn eval <E: Into<Box<dyn std::error::Error>>> (&self, args: &Args, error: impl Fn()->E)
         -> Usually<RetVal>
     {
         match self.try_eval(args)? {