Merge pull request #7 from purescript/deletions

Add delete, deleteBy, (\\)

Author: paf31

README.md

@@ -23,6 +23,8 @@
 
     (!!) :: forall a. [a] -> Prim.Number -> Maybe a
 
+    (\\) :: forall a. (Eq a) => [a] -> [a] -> [a]
+
     append :: forall a. [a] -> [a] -> [a]
 
     catMaybes :: forall a. [Maybe a] -> [a]
@@ -31,8 +33,12 @@
 
     concatMap :: forall a b. (a -> [b]) -> [a] -> [b]
 
+    delete :: forall a. (Eq a) => a -> [a] -> [a]
+
     deleteAt :: forall a. Prim.Number -> Prim.Number -> [a] -> [a]
 
+    deleteBy :: forall a. (a -> a -> Prim.Boolean) -> a -> [a] -> [a]
+
     drop :: forall a. Prim.Number -> [a] -> [a]
 
     elemIndex :: forall a. (Eq a) => a -> [a] -> Prim.Number

src/Data/Array.purs

@@ -23,6 +23,9 @@ module Data.Array
   , insertAt
   , deleteAt
   , updateAt
+  , deleteBy
+  , delete
+  , (\\)
   , concatMap
   , filter
   , range
@@ -193,6 +196,24 @@ foreign import updateAt
   \  };\
   \}":: forall a. Number -> a -> [a] -> [a]
 
+deleteBy :: forall a. (a -> a -> Boolean) -> a -> [a] -> [a]
+deleteBy _ _ [] = []
+deleteBy eq x ys = case findIndex (eq x) ys of
+  i | i < 0 -> ys
+  i -> deleteAt i 1 ys
+
+delete :: forall a. (Eq a) => a -> [a] -> [a]
+delete = deleteBy (==)
+
+infix 5 \\
+
+(\\) :: forall a. (Eq a) => [a] -> [a] -> [a]
+(\\) xs ys = go xs ys
+  where
+  go [] ys = ys
+  go _  [] = []
+  go (x:xs) ys = go xs (delete x ys)
+
 foreign import concatMap
   "function concatMap (f) {\
   \  return function (arr) {\