Continue Day10 Part2

1 files changed, 11 insertions, 0 deletions

diff --git a/Common/NonEmptyList.lean b/Common/NonEmptyList.lean
new file mode 100644
index 0000000..786e192
--- /dev/null
+++ b/Common/NonEmptyList.lean
@@ -0,0 +1,11 @@
+structure NonEmptyList (α : Type) where
+  head : α
+  tail : List α
+
+namespace NonEmptyList
+def toList (l : NonEmptyList α) : List α :=
+  l.head :: l.tail
+
+def ofList (l : List α) (_ : ¬l.isEmpty) : NonEmptyList α :=
+  match l with
+  | head :: tail => {head, tail}