custom-set-variables add blank space on subsequent uses

Question

I followed the emacs haskell tutorial, and couldn't understand some of its language regarding the use of custom-set-variables in the text quoted below. It seems that custom-set-variables should be used in one way on first usage, and another way (with added blank space) on subsequent uses.

My questions are:

What exactly should the second usage be?

Why is it that custom-set-variables should be used differently on first and subsequent usage?

Thanks

-- quoted code --

To enable it, add

(custom-set-variables '(haskell-process-type 'cabal-repl))

to your personal configuration file. However, if your personal configuration file already has a custom-set-variables command, you'll need to instead add a blank space and then '(haskell-process-type 'cabal-repl) before its closing parenthesis.

Answer 1

It's just saying that you can include multiple custom variables in one invocation of custom-set-variables. So if you already have

(custom-set-variables
  '(some-variable 'some-value))

you can add to it like so:

(custom-set-variables
  '(some-variable 'some-value)
  '(haskell-process-type 'cabal-repl))