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authorJoey Hess2015-01-24 16:54:49 -0400
committerJoey Hess2015-01-24 16:54:49 -0400
commit45c94ffdd79b4f8134ef651b08fedb57b37448e6 (patch)
treef6f156c9281d91654d1a7675841ac1bf3adab715 /src/Propellor/Info.hs
parent414ee7eee60300eb7f7c49e4890b056d19b3c59b (diff)
moving to using the GADT
The problem this exposes has to do with requires. As implemented, requires yields either a Property HasInfo or a Property NoInfo depending on its inputs. That works. But look what happens when it's used: *Propellor.Types> let foo = IProperty "foo" (return NoChange) mempty mempty *Propellor.Types> let bar = IProperty "bar" (return NoChange) mempty mempty *Propellor.Types> foo `requires` bar <interactive>:17:5: No instance for (Requires (Property HasInfo) (Property HasInfo) r0) arising from a use of `requires' The type variable `r0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) Note: there is a potential instance available: instance Requires (Property HasInfo) (Property HasInfo) (Property HasInfo) -- Defined at Propellor/Types.hs:167:10 Possible fix: add an instance declaration for (Requires (Property HasInfo) (Property HasInfo) r0) In the expression: foo `requires` bar In an equation for `it': it = foo `requires` bar This can be avoided by specifying the result type: *Propellor.Types> (foo `requires` bar) :: Property HasInfo property "foo" But then when multiple `requires` are given, the result type has to be given each time: *Propellor.Types> (foo `requires` bar `requires` bar) :: Property HasInfo <interactive>:22:6: No instance for (Requires (Property HasInfo) (Property HasInfo) x0) arising from a use of `requires' The type variable `x0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) Note: there is a potential instance available: instance Requires (Property HasInfo) (Property HasInfo) (Property HasInfo) -- Defined at Propellor/Types.hs:167:10 Possible fix: add an instance declaration for (Requires (Property HasInfo) (Property HasInfo) x0) In the first argument of `requires', namely `foo `requires` bar' In the expression: (foo `requires` bar `requires` bar) :: Property HasInfo In an equation for `it': it = (foo `requires` bar `requires` bar) :: Property HasInfo <interactive>:22:21: No instance for (Requires x0 (Property HasInfo) (Property HasInfo)) arising from a use of `requires' The type variable `x0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) Note: there are several potential instances: instance Requires (Property NoInfo) (Property HasInfo) (Property HasInfo) -- Defined at Propellor/Types.hs:175:10 instance Requires (Property HasInfo) (Property HasInfo) (Property HasInfo) -- Defined at Propellor/Types.hs:167:10 Possible fix: add an instance declaration for (Requires x0 (Property HasInfo) (Property HasInfo)) In the expression: (foo `requires` bar `requires` bar) :: Property HasInfo In an equation for `it': it = (foo `requires` bar `requires` bar) :: Property HasInfo *Propellor.Types> (((foo `requires` bar) :: Property HasInfo) `requires` bar) :: Property HasInfo property "foo" Yuggh!
Diffstat (limited to 'src/Propellor/Info.hs')
-rw-r--r--src/Propellor/Info.hs12
1 files changed, 6 insertions, 6 deletions
diff --git a/src/Propellor/Info.hs b/src/Propellor/Info.hs
index 6d85cb74..1d8e7ab2 100644
--- a/src/Propellor/Info.hs
+++ b/src/Propellor/Info.hs
@@ -12,13 +12,13 @@ import Data.Maybe
import Data.Monoid
import Control.Applicative
-pureInfoProperty :: Desc -> Info -> Property
+pureInfoProperty :: Desc -> Info -> Property HasInfo
pureInfoProperty desc i = mkProperty ("has " ++ desc) (return NoChange) i mempty
askInfo :: (Info -> Val a) -> Propellor (Maybe a)
askInfo f = asks (fromVal . f . hostInfo)
-os :: System -> Property
+os :: System -> Property HasInfo
os system = pureInfoProperty ("Operating " ++ show system) $
mempty { _os = Val system }
@@ -34,11 +34,11 @@ getOS = askInfo _os
-- When propellor --spin is used to deploy a host, it checks
-- if the host's IP Property matches the DNS. If the DNS is missing or
-- out of date, the host will instead be contacted directly by IP address.
-ipv4 :: String -> Property
+ipv4 :: String -> Property HasInfo
ipv4 = addDNS . Address . IPv4
-- | Indidate that a host has an AAAA record in the DNS.
-ipv6 :: String -> Property
+ipv6 :: String -> Property HasInfo
ipv6 = addDNS . Address . IPv6
-- | Indicates another name for the host in the DNS.
@@ -47,7 +47,7 @@ ipv6 = addDNS . Address . IPv6
-- to use their address, rather than using a CNAME. This avoids various
-- problems with CNAMEs, and also means that when multiple hosts have the
-- same alias, a DNS round-robin is automatically set up.
-alias :: Domain -> Property
+alias :: Domain -> Property HasInfo
alias d = pureInfoProperty ("alias " ++ d) $ mempty
{ _aliases = S.singleton d
-- A CNAME is added here, but the DNS setup code converts it to an
@@ -55,7 +55,7 @@ alias d = pureInfoProperty ("alias " ++ d) $ mempty
, _dns = S.singleton $ CNAME $ AbsDomain d
}
-addDNS :: Record -> Property
+addDNS :: Record -> Property HasInfo
addDNS r = pureInfoProperty (rdesc r) $ mempty { _dns = S.singleton r }
where
rdesc (CNAME d) = unwords ["alias", ddesc d]