In Emacs, how to use align-regexp to align <- and = together

I've tried, with M-x align-regexp:

<-|=
(<-|=)
\(<-|=\)
\\(<-|=\\)

And the ones with <- and = reversed. But none work?

Example code as follows:

  (flags, params, errs) <- parseArgs <$> getArgs
  let options = foldr id [] flags -- Apply functi开发者_如何学编程ons to list

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try \(<-\|=\) -- you need the (backslashed) parentheses, and you need to backslash the |

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You need to escape the |:

\(<-\|=\)