diff options
Diffstat (limited to 'compiler/utils/Util.hs')
| -rw-r--r-- | compiler/utils/Util.hs | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/compiler/utils/Util.hs b/compiler/utils/Util.hs index b8af6a7c9d..8cafbfb4f1 100644 --- a/compiler/utils/Util.hs +++ b/compiler/utils/Util.hs @@ -14,7 +14,7 @@ module Util ( zipEqual, zipWithEqual, zipWith3Equal, zipWith4Equal, zipLazy, stretchZipWith, zipWithAndUnzip, - filterByList, partitionByList, + filterByList, filterByLists, partitionByList, unzipWith, @@ -331,6 +331,23 @@ filterByList (True:bs) (x:xs) = x : filterByList bs xs filterByList (False:bs) (_:xs) = filterByList bs xs filterByList _ _ = [] +-- | 'filterByLists' takes a list of Bools and two lists as input, and +-- outputs a new list consisting of elements from the last two input lists. For +-- each Bool in the list, if it is 'True', then it takes an element from the +-- former list. If it is 'False', it takes an element from the latter list. +-- The elements taken correspond to the index of the Bool in its list. +-- For example: +-- +-- @ +-- filterByLists [True, False, True, False] \"abcd\" \"wxyz\" = \"axcz\" +-- @ +-- +-- This function does not check whether the lists have equal length. +filterByLists :: [Bool] -> [a] -> [a] -> [a] +filterByLists (True:bs) (x:xs) (_:ys) = x : filterByLists bs xs ys +filterByLists (False:bs) (_:xs) (y:ys) = y : filterByLists bs xs ys +filterByLists _ _ _ = [] + -- | 'partitionByList' takes a list of Bools and a list of some elements and -- partitions the list according to the list of Bools. Elements corresponding -- to 'True' go to the left; elements corresponding to 'False' go to the right. |