Question

I have heard the term ‘list difference’ (\\) operator in Haskell but still don’t quite know how to get my head around it. Any examples or ideas?

Answer 1

Simply put, it takes two lists, goes through the second and for each item, removes the first instance of the same item from the first list.

> [1..10] \\ [2, 3, 5, 8]
[1,4,6,7,9,10]
> [1, 2, 1, 2, 1, 2] \\ [2]
[1,1,2,1,2]
> [1, 2, 1, 2, 1, 2] \\ [2, 2]
[1,1,1,2]
> [1, 2, 1, 2, 1, 2] \\ [2, 2, 1]
[1,1,2]