[[!comment format=mdwn
 username="joey"
 subject="""comment 5"""
 date="2017-02-03T19:32:58Z"
 content="""
What you're looking for is not a regexp, but Haskell's [pattern
matching](https://www.haskell.org/tutorial/patterns.html).

For example:

	myproperty :: Property Debian
	myproperty = withOS "some desc here" $ \w o -> case o of
		-- Pattern match on the OS, to get the Debian stable release
		(Just (System (Debian _kernel (Stable release)) _arch)) ->
			ensureProperty w $ Apt.setSourcesListD (sourcesLines release) "mysources"
		_ -> unsupportedOS

	sourcesLines :: Release -> [Line]
	sourcesLines release = undefined
"""]]
