diff options
Diffstat (limited to 'Common/NonEmptyList.lean')
| -rw-r--r-- | Common/NonEmptyList.lean | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Common/NonEmptyList.lean b/Common/NonEmptyList.lean index 786e192..6e76f89 100644 --- a/Common/NonEmptyList.lean +++ b/Common/NonEmptyList.lean @@ -9,3 +9,12 @@ def toList (l : NonEmptyList α) : List α := def ofList (l : List α) (_ : ¬l.isEmpty) : NonEmptyList α := match l with | head :: tail => {head, tail} + +def ofList? (l : List α) : Option $ NonEmptyList α := + if h : l.isEmpty then + none + else + ofList l h + +instance [ToString α] : ToString (NonEmptyList α) where + toString := List.toString ∘ toList |