feat: reduce + fold

mute-interpreter/src/evaluator.rs

@@ -285,8 +285,62 @@ pub fn eval_node(env: &Environment, ast_node: Node) -> Result<Node> {
 
             Node::List(res)
         }
-        Node::Reduce(mut body) => todo!(),
+        Node::Reduce(mut body) => {
-        Node::Fold(mut body) => todo!(),
+            if body.len() != 2 {
+                todo!();
+            }
+
+            let list = body.pop_front().expect("arg count verified above");
+            let mut list = match eval_node(env, list)? {
+                Node::List(list) => list,
+                _ => todo!(),
+            };
+
+            let func = match body.pop_front().expect("arg count verified above") {
+                node @ Node::Function(_) => node,
+                node @ Node::Symbol(_) => eval_node(env, node)?,
+                _ => todo!(),
+            };
+
+            let mut acc = match list.pop_front() {
+                Some(node) => eval_node(env, node)?,
+                None => Node::Nil,
+            };
+
+            while let Some(node) = list.pop_front() {
+                let node = eval_node(env, node)?;
+                acc = eval_node(env, Node::List(vec![func.clone(), acc, node].into()))?;
+            }
+
+            acc
+        }
+
+        Node::Fold(mut body) => {
+            if body.len() != 3 {
+                todo!();
+            }
+
+            let list = body.pop_front().expect("arg count verified above");
+            let mut list = match eval_node(env, list)? {
+                Node::List(list) => list,
+                _ => todo!(),
+            };
+
+            let mut acc = body.pop_front().expect("arg count verified above");
+
+            let func = match body.pop_front().expect("arg count verified above") {
+                node @ Node::Function(_) => node,
+                node @ Node::Symbol(_) => eval_node(env, node)?,
+                _ => todo!(),
+            };
+
+            while let Some(node) = list.pop_front() {
+                let node = eval_node(env, node)?;
+                acc = eval_node(env, Node::List(vec![func.clone(), acc, node].into()))?;
+            }
+
+            acc
+        }
 
         Node::Symbol(sym) => env
             .get_node(&sym)
@@ -484,6 +538,10 @@ mod test {
     // Iteration
     #[case("(map '(1 2 3) (fn* (x) (* x x)))", "(1 4 9)")]
     #[case("(filter '(1 2 3) (fn* (x) (> x 1)))", "(2 3)")]
+    #[case("(reduce '(1 2 3 4) +)", "10")]
+    #[case("(reduce '(1 2 3 4) (fn* (lhs rhs) (+ lhs rhs)))", "10")]
+    #[case("(fold '(1 2 3 4) 5 +)", "15")]
+    #[case("(fold '(1 2 3 4) 5 (fn* (lhs rhs) (+ lhs rhs)))", "15")]
     fn test_evaluator(#[case] input: &str, #[case] expected: &str) {
         dbg!(input);