separate Input and Output impls

engine/src/event_map.rs

@@ -0,0 +1,43 @@
+use crate::*;
+
+pub struct EventMap<'a, S, I: PartialEq, C> {
+    pub bindings: &'a [(I, &'a dyn Fn(&S) -> Option<C>)],
+    pub fallback: Option<&'a dyn Fn(&S, &I) -> Option<C>>
+}
+impl<'a, S, I: PartialEq, C> EventMap<'a, S, I, C> {
+    pub fn handle (&self, state: &S, input: &I) -> Option<C> {
+        for (binding, handler) in self.bindings.iter() {
+            if input == binding {
+                return handler(state)
+            }
+        }
+        if let Some(fallback) = self.fallback {
+            fallback(state, input)
+        } else {
+            None
+        }
+    }
+}
+
+#[macro_export] macro_rules! keymap {
+    (
+        $(<$lt:lifetime>)? $KEYS:ident = |$state:ident: $State:ty, $input:ident: $Input:ty| $Command:ty
+        { $($key:expr => $handler:expr),* $(,)? } $(,)?
+    ) => {
+        pub const $KEYS: EventMap<'static, $State, $Input, $Command> = EventMap {
+            fallback: None,
+            bindings: &[ $(($key, &|$state|Some($handler)),)* ]
+        };
+        input_to_command!($(<$lt>)? $Command: |$state: $State, input: $Input|$KEYS.handle($state, input)?);
+    };
+    (
+        $(<$lt:lifetime>)? $KEYS:ident = |$state:ident: $State:ty, $input:ident: $Input:ty| $Command:ty
+        { $($key:expr => $handler:expr),* $(,)? }, $default:expr
+    ) => {
+        pub const $KEYS: EventMap<'static, $State, $Input, $Command> = EventMap {
+            fallback: Some(&|$state, $input|Some($default)),
+            bindings: &[ $(($key, &|$state|Some($handler)),)* ]
+        };
+        input_to_command!($(<$lt>)? $Command: |$state: $State, input: $Input|$KEYS.handle($state, input)?);
+    };
+}