>>> elemIndices 'o' "Hello World" [4,7]
elemIndices a = findIndices (== a)
>>> elemIndices a = Fold.findIndices (== a)
>>> elemIndices a = Stream.findIndices (== a)
>>> elemIndices 1 $ unsafeFromList [1,2,3,1] [0,3]
>>> elemIndices 0 $ unsafeFromList [1..3] []