summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorGravatar Alexander Abushkevich <alex@abushkevi.ch>2016-02-23 00:49:17 +1300
committerGravatar Alexander Abushkevich <alex@abushkevi.ch>2016-02-23 01:30:31 +1300
commit746e16d83aaf284f996bcc6d61f0d9ba99c099b2 (patch)
tree8312b8bdcce9d7ef468abb6e86d0dc3a4d97b5e4
parent5705d3b510277f033b8a0317b3fe520b0e5cc60a (diff)
Find longest prefix of elements, which satisfy a predicate; Group a list
-rw-r--r--lib/ur/list.ur25
-rw-r--r--lib/ur/list.urs6
2 files changed, 31 insertions, 0 deletions
diff --git a/lib/ur/list.ur b/lib/ur/list.ur
index 11895884..f3bb0587 100644
--- a/lib/ur/list.ur
+++ b/lib/ur/list.ur
@@ -434,6 +434,31 @@ fun drop [a] (n : int) (xs : list a) : list a =
fun splitAt [a] (n : int) (xs : list a) : list a * list a =
(take n xs, drop n xs)
+
+fun span [a] (f:(a -> bool)) (ls:list a) : list a * list a =
+ let
+ fun span' f acc ls =
+ case ls of
+ [] => (acc, [])
+ | x :: xs => if (f x) then span' f (x :: acc) xs else (acc, ls)
+ in
+ span' f [] ls
+ end
+
+fun groupBy [a] (f:(a -> a -> bool)) (ls:list a) : list (list a) =
+ let
+ fun groupBy' f ls =
+ case ls of
+ [] => [] :: []
+ | x :: xs =>
+ let
+ val (ys, zs) = span (f x) xs
+ in
+ (x :: ys) :: (groupBy' f zs)
+ end
+ in
+ groupBy' f ls
+ end
fun mapXiM [m ::: Type -> Type] (_ : monad m) [a] [ctx ::: {Unit}] (f : int -> a -> m (xml ctx [] [])) : t a -> m (xml ctx [] []) =
let
diff --git a/lib/ur/list.urs b/lib/ur/list.urs
index 55068935..ac874d7c 100644
--- a/lib/ur/list.urs
+++ b/lib/ur/list.urs
@@ -105,3 +105,9 @@ val recToList : a ::: Type -> r ::: {Unit} -> folder r -> $(mapU a r) -> t a
val drop : t ::: Type -> int -> list t -> list t
val take : t ::: Type -> int -> list t -> list t
val splitAt : t ::: Type -> int -> list t -> list t * list t
+
+(** Longest prefix of elements, which satisfy a predicate *)
+val span : a ::: Type -> (a -> bool) -> t a -> t a * t a
+
+(** Group a list *)
+val groupBy : a ::: Type -> (a -> a -> bool) -> t a -> t (t a)