Add program::Preset and emulator::Mode

program/src/preset.rs

@@ -0,0 +1,42 @@
+use crate::runtime::Task;
+
+use std::borrow::Cow;
+use std::fmt;
+
+/// A specific boot strategy for a [`Program`].
+pub struct Preset<State, Message> {
+    name: Cow<'static, str>,
+    boot: Box<dyn Fn() -> (State, Task<Message>)>,
+}
+
+impl<State, Message> Preset<State, Message> {
+    /// Creates a new [`Preset`] with the given name and boot strategy.
+    pub fn new(
+        name: impl Into<Cow<'static, str>>,
+        boot: impl Fn() -> (State, Task<Message>) + 'static,
+    ) -> Self {
+        Self {
+            name: name.into(),
+            boot: Box::new(boot),
+        }
+    }
+
+    /// Returns the name of the [`Preset`].
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// Boots the [`Preset`], returning the initial [`Program`] state and
+    /// a [`Task`] for concurrent booting.
+    pub fn boot(&self) -> (State, Task<Message>) {
+        (self.boot)()
+    }
+}
+
+impl<State, Message> fmt::Debug for Preset<State, Message> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Preset")
+            .field("name", &self.name)
+            .finish_non_exhaustive()
+    }
+}