tabula rasa

input/src/command.rs

@@ -0,0 +1,28 @@
+use crate::*;
+#[macro_export] macro_rules! command {
+    ($(<$($l:lifetime),+>)?|$self:ident:$Command:ty,$state:ident:$State:ty|$handler:expr) => {
+        impl$(<$($l),+>)? Command<$State> for $Command {
+            fn execute ($self, $state: &mut $State) -> Perhaps<Self> {
+                Ok($handler)
+            }
+        }
+    };
+}
+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)
+    }
+}