2 files changed, 52 insertions, 0 deletions
diff --git a/rprt-engine/src/lib.rs b/rprt-engine/src/lib.rs
index 3ef4ac1..0ae9d2d 100644
--- a/rprt-engine/src/lib.rs
+++ b/rprt-engine/src/lib.rs
@@ -2,6 +2,7 @@
 
 pub mod buffer;
 pub mod expression;
+pub mod monad;
 pub mod parser;
 pub mod selection;
 pub mod state;
diff --git a/rprt-engine/src/monad.rs b/rprt-engine/src/monad.rs
new file mode 100644
index 0000000..ae0df3e
--- /dev/null
+++ b/rprt-engine/src/monad.rs
@@ -0,0 +1,51 @@
+use crate::{
+    selection::Selection,
+    state::{EditorState, EvaluationResult},
+};
+
+pub enum EvaluationStrategy {
+    Sequential,
+    Grouped,
+}
+
+pub type MonadicState = (EditorState, EvaluationResult);
+
+pub struct EditorStateMonad {
+    func: Box<dyn Fn(EditorState) -> MonadicState>,
+}
+
+impl EditorStateMonad {
+    pub fn new(f: impl Fn(EditorState) -> MonadicState + 'static) -> Self {
+        Self { func: Box::new(f) }
+    }
+
+    pub fn run(&self, initial_state: EditorState) -> MonadicState {
+        (self.func)(initial_state)
+    }
+
+    pub fn run_with_strategy<E>(
+        monads: Vec<EditorStateMonad>,
+        strategy: EvaluationStrategy,
+        initial_state: EditorState,
+    ) -> Result<MonadicState, E> {
+        match strategy {
+            EvaluationStrategy::Sequential => {
+                let mut state_changes = Vec::new();
+                let mut last_selection = Selection::empty();
+                let mut current_state = initial_state;
+
+                for monad in monads {
+                    let (new_state, (sel, st_ch)) = monad.run(current_state);
+                    current_state = new_state;
+                    last_selection = sel;
+                    state_changes.extend(st_ch);
+                }
+
+                Ok((current_state, (last_selection, state_changes)))
+            }
+            EvaluationStrategy::Grouped => {
+                panic!("TODO")
+            }
+        }
+    }
+}