diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/todo/differential_update_via_RevertableProperty.mdwn | 25 |
1 files changed, 8 insertions, 17 deletions
diff --git a/doc/todo/differential_update_via_RevertableProperty.mdwn b/doc/todo/differential_update_via_RevertableProperty.mdwn index 6d65c916..3eb9bc7a 100644 --- a/doc/todo/differential_update_via_RevertableProperty.mdwn +++ b/doc/todo/differential_update_via_RevertableProperty.mdwn @@ -101,33 +101,23 @@ Is, perhaps: data Version = A | B | C deriving (Enum, Ord) - foo :: Versioned Host + foo :: Versioned Hoso foo = versionedHost "foo" $ do ver A someprop - <|> inVersion [B, C] otherprop + <|> othervers otherprop ver A somerevertableprop - ver [B, C] somethingelse + ver [B, C] newprop That's ... pretty ok, would hit as least some of the use cases described above. Seems to need a Reader+Writer monad to implement it, without passing the Version around explicitly. -Is it allowable for `somethingelse` to not be revertable? +Is it allowable for `newprop` to not be revertable? Once `foo` gets that property, it is never removed if we're moving only -forwars. On the other hand, perhaps the user will want to roll back to +forwards. On the other hand, perhaps the user will want to roll back to version A. Allowing rollbacks seems good, so `inVersion` should only accept `RevertableProperty`. -Here's another situation where reversion is not needed: - - foo = versionedHost "foo" $ do - ver A (someprop :: Property) - <|> ver [B, C] (someprop :: Property) - -That feels like an edge case.. And the only way that propellor could tell -reversion is not needed there is if it could compare the two sides of the -`<|>`, and there's no Eq. - Another interesting case is this: foo = versionedHost "foo" $ do @@ -151,5 +141,6 @@ examples above. And that allows composition of properties with versioning: someprop :: Versioned (Property DebianLike) someprop = versionedProperty $ do - ver A foo - ver [B, C] bar + ver A foo <|> ver [B, C] bar + +> [[done]] in Propellor.Property.Versioned. --[[Joey]] |