in midst of refactor

orchid-base/src/combine.rs

@@ -0,0 +1,24 @@
+//! The concept of a fallible merger
+
+use never::Never;
+
+/// Fallible, type-preserving variant of [std::ops::Add] implemented by a
+/// variety of types for different purposes. Very broadly, if the operation
+/// succeeds, the result should represent _both_ inputs.
+pub trait Combine: Sized {
+  /// Information about the failure
+  type Error;
+
+  /// Merge two values into a value that represents both, if this is possible.
+  fn combine(self, other: Self) -> Result<Self, Self::Error>;
+}
+
+impl Combine for Never {
+  type Error = Never;
+  fn combine(self, _: Self) -> Result<Self, Self::Error> { match self {} }
+}
+
+impl Combine for () {
+  type Error = Never;
+  fn combine(self, (): Self) -> Result<Self, Self::Error> { Ok(()) }
+}