input: add InputMap; dsl/output/tui: Atom->Dsl

input/src/input_command.rs

@@ -0,0 +1,21 @@
+use crate::*;
+
+pub trait Command<S>: Send + Sync + Sized {
+    fn execute (self, state: &mut S) -> Perhaps<Self>;
+    fn delegate <T> (self, state: &mut S, wrap: impl Fn(Self)->T) -> Perhaps<T>
+        where Self: Sized
+    {
+        Ok(self.execute(state)?.map(wrap))
+    }
+}
+
+impl<S, T: Command<S>> Command<S> for Option<T> {
+    fn execute (self, _: &mut S) -> Perhaps<Self> {
+        Ok(None)
+    }
+    fn delegate <U> (self, _: &mut S, _: impl Fn(Self)->U) -> Perhaps<U>
+        where Self: Sized
+    {
+        Ok(None)
+    }
+}