diff options
| -rw-r--r-- | lib/ur/list.ur | 26 | ||||
| -rw-r--r-- | lib/ur/list.urs | 4 | ||||
| -rw-r--r-- | tests/groupBy.ur | 3 | ||||
| -rw-r--r-- | tests/groupBy.urp | 4 |
4 files changed, 22 insertions, 15 deletions
diff --git a/lib/ur/list.ur b/lib/ur/list.ur index eac5ab0c..50764e46 100644 --- a/lib/ur/list.ur +++ b/lib/ur/list.ur @@ -435,29 +435,29 @@ 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 = +fun span [a] (f : a -> bool) (ls : list a) : list a * list a = let - fun span' f acc ls = + fun span' ls acc = case ls of [] => (rev acc, []) - | x :: xs => if (f x) then span' f (x :: acc) xs else (rev acc, ls) + | x :: xs => if f x then span' xs (x :: acc) else (rev acc, ls) in - span' f [] ls + span' ls [] end -fun groupBy [a] (f:(a -> a -> bool)) (ls:list a) : list (list a) = +fun groupBy [a] (f : a -> a -> bool) (ls : list a) : list (list a) = let - fun groupBy' f ls = + fun groupBy' ls acc = case ls of - [] => [] :: [] + [] => rev ([] :: acc) | x :: xs => - let - val (ys, zs) = span (f x) xs - in - (x :: ys) :: (groupBy' f zs) - end + let + val (ys, zs) = span (f x) xs + in + groupBy' zs ((x :: ys) :: acc) + end in - groupBy' f ls + groupBy' ls [] end fun mapXiM [m ::: Type -> Type] (_ : monad m) [a] [ctx ::: {Unit}] (f : int -> a -> m (xml ctx [] [])) : t a -> m (xml ctx [] []) = diff --git a/lib/ur/list.urs b/lib/ur/list.urs index ac874d7c..432d8c1a 100644 --- a/lib/ur/list.urs +++ b/lib/ur/list.urs @@ -106,8 +106,8 @@ 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 *) +(** Longest prefix of elements that satisfy a predicate, returned along with the remaining suffix *) val span : a ::: Type -> (a -> bool) -> t a -> t a * t a -(** Group a list *) +(** Group a list into maximal adjacent segments where all elements compare as equal, according to the provided predicate. *) val groupBy : a ::: Type -> (a -> a -> bool) -> t a -> t (t a) diff --git a/tests/groupBy.ur b/tests/groupBy.ur new file mode 100644 index 00000000..e91e33cc --- /dev/null +++ b/tests/groupBy.ur @@ -0,0 +1,3 @@ +val main : transaction page = return <xml><body> + {[List.groupBy eq (1 :: 1 :: 2 :: 2 :: 3 :: 4 :: 4 :: 4 :: 5 :: [])]} +</body></xml> diff --git a/tests/groupBy.urp b/tests/groupBy.urp new file mode 100644 index 00000000..de1db792 --- /dev/null +++ b/tests/groupBy.urp @@ -0,0 +1,4 @@ +rewrite all GroupBy/* + +$/list +groupBy |