Merge pull request #8 from purescript/intersect

Add unsafeLast, intersect(By)

Author: garyb

README.md

@@ -63,6 +63,10 @@
 
     insertAt :: forall a. Prim.Number -> a -> [a] -> [a]
 
+    intersect :: forall a. (Eq a) => [a] -> [a] -> [a]
+
+    intersectBy :: forall a. (a -> a -> Prim.Boolean) -> [a] -> [a] -> [a]
+
     last :: forall a. [a] -> Maybe a
 
     length :: forall a. [a] -> Prim.Number
@@ -106,4 +110,6 @@
 
     head :: forall a. [a] -> a
 
+    last :: forall a. [a] -> a
+
     tail :: forall a. [a] -> [a]

src/Data/Array.purs

@@ -26,6 +26,8 @@ module Data.Array
   , deleteBy
   , delete
   , (\\)
+  , intersectBy
+  , intersect
   , concatMap
   , filter
   , range
@@ -214,6 +216,16 @@ infix 5 \\
   go _  [] = []
   go (x:xs) ys = go xs (delete x ys)
 
+intersectBy :: forall a. (a -> a -> Boolean) -> [a] -> [a] -> [a]
+intersectBy _  [] _  = []
+intersectBy _  _  [] = []
+intersectBy eq xs ys = filter el xs
+  where
+  el x = findIndex (eq x) ys >= 0
+
+intersect :: forall a. (Eq a) => [a] -> [a] -> [a]
+intersect = intersectBy (==)
+
 foreign import concatMap
   "function concatMap (f) {\
   \  return function (arr) {\

src/Data/Array/Unsafe.purs

@@ -1,7 +1,13 @@
 module Data.Array.Unsafe where
 
+import Prelude.Unsafe
+import Data.Array (length)
+
 head :: forall a. [a] -> a
 head (x : _) = x
 
 tail :: forall a. [a] -> [a]
 tail (_ : xs) = xs
+
+last :: forall a. [a] -> a
+last xs = unsafeIndex xs (length xs - 1)