From 4f67fe6cd314ad3ca1286766f1f9f3d8c5084d48 Mon Sep 17 00:00:00 2001 From: Adam Chlipala Date: Sun, 11 Dec 2011 15:02:55 -0500 Subject: Some new List functions, based on code by Ron de Bruijn --- lib/ur/list.ur | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'lib/ur/list.ur') diff --git a/lib/ur/list.ur b/lib/ur/list.ur index 6a754287..2d5addc9 100644 --- a/lib/ur/list.ur +++ b/lib/ur/list.ur @@ -267,6 +267,18 @@ fun foldlMi [m] (_ : monad m) [a] [b] f = foldlMi' 0 end +fun filterM [m] (_ : monad m) [a] (p : a -> m bool) = + let + fun filterM' (acc : list a) (xs : list a) : m (list a) = + case xs of + [] => return (rev acc) + | x :: xs => + c <- p x; + filterM' (if c then x :: acc else acc) xs + in + filterM' [] + end + fun all [m] f = let fun all' ls = @@ -393,3 +405,22 @@ fun assocAdd [a] [b] (_ : eq a) (x : a) (y : b) (ls : t (a * b)) = fun recToList [a ::: Type] [r ::: {Unit}] (fl : folder r) = @foldUR [a] [fn _ => list a] (fn [nm ::_] [rest ::_] [[nm] ~ rest] x xs => x :: xs) [] fl + +fun take [a] (n : int) (xs : list a) : list a = + if n <= 0 then + [] + else + case xs of + [] => [] + | x :: xs => x :: take (n-1) xs + +fun drop [a] (n : int) (xs : list a) : list a = + if n <= 0 then + xs + else + case xs of + [] => [] + | x :: xs => drop (n-1) xs + +fun splitAt [a] (n : int) (xs : list a) : list a * list a = + (take n xs, drop n xs) -- cgit v1.2.3