semblance of groovebox launches from edn layout!

layout/src/either.rs

@@ -0,0 +1,16 @@
+use crate::*;
+
+/// Show one item if a condition is true and another if the condition is false
+pub struct Either<A, B>(pub bool, pub A, pub B);
+
+impl<E: Output, A: Render<E>, B: Render<E>> Content<E> for Either<A, B> {
+    fn layout (&self, to: E::Area) -> E::Area {
+        let Self(cond, a, b) = self;
+        if *cond { a.layout(to) } else { b.layout(to) }
+    }
+    fn render (&self, to: &mut E) {
+        let Self(cond, a, b) = self;
+        if *cond { a.render(to) } else { b.render(to) }
+    }
+}
+