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| -rw-r--r-- | doc/forum/howto_mapM_RevertableProperty/comment_1_c2800340a5361add82f5e9e30b56b18c._comment | 22 |
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diff --git a/doc/forum/howto_mapM_RevertableProperty/comment_1_c2800340a5361add82f5e9e30b56b18c._comment b/doc/forum/howto_mapM_RevertableProperty/comment_1_c2800340a5361add82f5e9e30b56b18c._comment new file mode 100644 index 00000000..66ac9a4f --- /dev/null +++ b/doc/forum/howto_mapM_RevertableProperty/comment_1_c2800340a5361add82f5e9e30b56b18c._comment @@ -0,0 +1,22 @@ +[[!comment format=mdwn + username="joey" + subject="""comment 1""" + date="2016-02-08T15:00:26Z" + content=""" +combineProperties takes a list of PropertyListType, which is a type family +consisting of [Property NoInfo] and [Property HasInfo]. So, you need to get +from RevertableProperty NoInfo to one of those. `toProp` can do that. + + combineProperties "desc" (map (toProp . myProperty) confs) + +But! I had a look and it was easy to make [RevertableProperty i] an +instance of PropertyListType, which makes what you already tried type check +too. I've done so in git. + +It would perhaps be nice to make lists of various sorts of properties +instances of Traversable, so that mapM etc could be used over them. That +would need some kind of monad for combining properties though, which does +not currently exist. Might make more sense to make an instance of Foldable +or just Monoid for properties. Any improvements in this area would be +appreciated! +"""]] |