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authorJoey Hess2015-11-01 11:30:36 -0400
committerJoey Hess2015-11-01 11:30:36 -0400
commit046d7d82b4b309ade5e3508817f1b9b684e57b94 (patch)
treeb1e6cc3f2d959c7726e3da0c67551927d6a321c8 /doc
parent082bfc9f301adc59d7cd26954d8cdc0caf80ec7e (diff)
parentb218820da0b069e826507150cba118f0fa69d409 (diff)
Merge branch 'joeyconfig'
Diffstat (limited to 'doc')
-rw-r--r--doc/todo/RevertableProperty_with_NoInfo.mdwn30
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diff --git a/doc/todo/RevertableProperty_with_NoInfo.mdwn b/doc/todo/RevertableProperty_with_NoInfo.mdwn
index 3b4a61a9..1aea0a04 100644
--- a/doc/todo/RevertableProperty_with_NoInfo.mdwn
+++ b/doc/todo/RevertableProperty_with_NoInfo.mdwn
@@ -16,3 +16,33 @@ a mouthful!
Since only 2 places in the propellor source code currently need to deal
with this, it doesn't currently seem worth making the change, unless a less
intrusive way can be found.
+
+> Hmm.. I'm not sure what I meant by that last paragraph, but I'm sure
+> this wart is annoying in more than 2 places by now. --[[Joey]]
+
+> Would be nice to instead have `RevertableProperty i`, where the i was inherited
+> from the currently active property. This would be less of a mouthful,
+> and models the info transfer correctly. Ie, if I have a
+> RevertableProperty that includes dns settings on its setup side,
+> reverting it means dropping those dns settings, so the result is NoInfo.
+
+> Unfortunately, when I tried to implement this, the types prevented it.
+> In particular, anything to do with the second property in a
+> `RevertableProperty i` is a problem because we don't know what
+> type of Property it is. For example:
+
+ data RevertableProperty i where
+ RIProperty :: Property HasInfo -> Property i -> RevertableProperty HasInfo
+ RSProperty :: Property NoInfo -> Property i -> RevertableProperty NoInfo
+
+ activeProperty :: RevertableProperty i -> Property i
+ activeProperty (RIProperty p _) = p
+ activeProperty (RSProperty p _) = p
+
+ inactiveProperty :: RevertableProperty i -> Property x
+
+> The x is unknown and cannot be deduced from the available types.
+>
+> What could be done, instead, is to make a `RevertableProperty i` specify
+> the info of both its sides. While this doesn't perfectly model
+> the info propigation, the types work. [[done]] --[[Joey]]