diff options
| author | Joey Hess <joey@kitenet.net> | 2014-11-19 18:57:58 -0400 |
|---|---|---|
| committer | Joey Hess <joey@kitenet.net> | 2014-11-19 18:57:58 -0400 |
| commit | 08242e29f6878cbf514bdf68a4a7276d514a6aba (patch) | |
| tree | 81f18ad959f5cdeae842296e4ee9e06b35533141 /src/Propellor/Property.hs | |
| parent | 5c34a575c835c061dc68025292e003786f60490e (diff) | |
add fallback combinator
Diffstat (limited to 'src/Propellor/Property.hs')
| -rw-r--r-- | src/Propellor/Property.hs | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/src/Propellor/Property.hs b/src/Propellor/Property.hs index 4b957317..9545979c 100644 --- a/src/Propellor/Property.hs +++ b/src/Propellor/Property.hs @@ -89,6 +89,15 @@ check c p = adjustProperty p $ \satisfy -> ifM (liftIO c) , return NoChange ) +-- | Tries the first property, but if it fails to work, instead uses +-- the second. +fallback :: Property -> Property -> Property +fallback p1 p2 = adjustProperty p1 $ \satisfy -> do + r <- satisfy + if r == FailedChange + then propertySatisfy p2 + else return r + -- | Marks a Property as trivial. It can only return FailedChange or -- NoChange. -- |