From cd8c6114229a5f725bd1818f1fc2d0538c40f486 Mon Sep 17 00:00:00 2001 From: Joey Hess Date: Mon, 1 Dec 2014 11:53:40 -0400 Subject: add question (taken from email) and answer --- doc/forum/property_combinator_ordering.mdwn | 8 ++++++ ...ent_1_0ea2186b5cfa7eadaf38ac2e97fc4a2c._comment | 31 ++++++++++++++++++++++ 2 files changed, 39 insertions(+) create mode 100644 doc/forum/property_combinator_ordering.mdwn create mode 100644 doc/forum/property_combinator_ordering/comment_1_0ea2186b5cfa7eadaf38ac2e97fc4a2c._comment (limited to 'doc') diff --git a/doc/forum/property_combinator_ordering.mdwn b/doc/forum/property_combinator_ordering.mdwn new file mode 100644 index 00000000..25549bb4 --- /dev/null +++ b/doc/forum/property_combinator_ordering.mdwn @@ -0,0 +1,8 @@ +when I write + + setDistribution cfg = f `File.hasContent` cfg + `onChange` update + `requires` File.dirExists confDir + +is update called before ensuring the confiDir Exist ? +It seems to me but who knows ? diff --git a/doc/forum/property_combinator_ordering/comment_1_0ea2186b5cfa7eadaf38ac2e97fc4a2c._comment b/doc/forum/property_combinator_ordering/comment_1_0ea2186b5cfa7eadaf38ac2e97fc4a2c._comment new file mode 100644 index 00000000..c41abd90 --- /dev/null +++ b/doc/forum/property_combinator_ordering/comment_1_0ea2186b5cfa7eadaf38ac2e97fc4a2c._comment @@ -0,0 +1,31 @@ +[[!comment format=mdwn + username="joey" + subject="""comment 1""" + date="2014-12-01T15:53:11Z" + content=""" +I think that should behave intuitively, but of course if you're unsure +of this kind of thing, adding parens is a good way to disambiguate the +code. + + (f `File.hasContent` cfg `onChange` update) + `requires` File.dirExists confDir + +Written that way, it's explicit that the parenthesized part runs +together as one action. + +Or, we can do a quick test in ghci: + + joey@darkstar:~/src/propellor/src#joeyconfig>ghci Propellor.hs Propellor/Property.hs + *Propellor> let f1 = property "hasContent" (liftIO (print "f1") >> return MadeChange) + *Propellor> let f2 = property "update" (liftIO (print "f2") >> return MadeChange) + *Propellor> let f3 = property "dirExists" (liftIO (print "f3") >> return MadeChange) + *Propellor> runPropellor (Host "foo" [] mempty) $ ensureProperty $ f1 `onChange` f2 `requires` f3 + "dirExists" + "hasContent" + "update" + MadeChange + +So, yes, it's behaving as it should, first ensuring that the `requires` +property is met, and then running the main property, and since it made a +change, following up by running the `onChange` property. +"""]] -- cgit v1.2.3