From 74863e1dbbc0f6c4c210d4674ea30886b9f42989 Mon Sep 17 00:00:00 2001
From: sun-jacobi <sun1011jacobi@gmail.com>
Date: Tue, 30 Jul 2024 10:30:45 +0200
Subject: [PATCH] Add List::split_first and List::split_last

---
 libspecr/src/list/func.rs | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/libspecr/src/list/func.rs b/libspecr/src/list/func.rs
index 9e7506f..9115b22 100644
--- a/libspecr/src/list/func.rs
+++ b/libspecr/src/list/func.rs
@@ -106,6 +106,28 @@ impl<T: Obj> List<T> {
         List(GcCow::new(v))
     }
 
+    /// Returns the first element and the rest of the list.
+    /// Returns `None` if the list is empty.
+    pub fn split_first(&self) -> Option<(T, List<T>)> {
+        if let Some(first) = self.first() {
+            let rest = self.subslice_with_length(Int::ONE, self.len() - Int::ONE);
+            Some((first, rest))
+        } else {
+            None
+        }
+    }
+
+    /// Returns the last element and the rest of the list.
+    /// Returns `None` if the list is empty.
+    pub fn split_last(&self) -> Option<(T, List<T>)> {
+        if let Some(last) = self.last() {
+            let rest = self.subslice_with_length(Int::ZERO, self.len() - Int::ONE);
+            Some((last, rest))
+        } else {
+            None
+        }
+    }
+
     /// Conceptually equivalent to `self[start..src.len()] = src;`
     pub fn write_subslice_at_index(&mut self, start: Int, src: List<T>) {
         // exclusive end