On 08/11/2014 05:04 PM, adam vogt wrote:
Hi Mateusz,
You can write 'Foo :~> [t| Maybe String |] to make the generated code include a
type instance App ElF Foo = Maybe String
Unfortunately the type of (:~>) includes some un-exported classes, so you have to dig into vinyl's source to see which arguments are actually allowed.
I'm not sure exactly what you mean by
PlainRec ElF (ParentId ': '[])” works but is ugly
But maybe it's worth just using the Data.Vinyl.Universe.Field (ex. http://lpaste.net/109203), if you would rather write
PlainRec ElField '["parent_id" ::: Maybe Integer])
than,
PlainRec ElF '[ParentId]
Or maybe you want to use Symbol together with your own universe:
makeUniverse' ''Symbol "ElF" semantics ''ElF [ [t| "height" |] :~> [t| Maybe Int |] ] -- type instance App ElF "height" = Maybe Int -- or just write those by-hand
height = Proxy :: Proxy "height" -- there seems to be no code generation in Vinyl for these
which will give you a type like
PlainRec ElF '["parent_id"]
Hopefully one of these options is not as ugly as the other.
Regards, Adam
Hi, I have managed to migrate to 0.4, thank you very much with these instructions. I'll outline what I ended up having to do in case anyone stumbles upon this thread in the future. I ended up going with makeUniverse' ''Symbol "ElF" way. This made the migration fairly mechanical. The reason for going this way rather than the others is that I don't have to define separate field type and mess around with singletons. For my application, it's important to me that the field names match up what they are in raw data so it was great I could keep using these. First I turned all foo :: "foo" ::: Bar foo = Field into foo :: Proxy "foo" foo = Proxy Easy with a macro. Likewise, I was able to turn the old field code into the [t| "foo" |] :~> [t| Bar |] style through some emacs macros. I also used ‘type R a = PlainRec ElF a’. With all these things in place, I simply had to remove every occurance of ‘ ::: SomeType’ and replace all ‘PlainRec whatever’ with ‘R whatever’. I also had a single ‘Rec’ in a combinator I defined but that also was easy to replace with ‘R’. Once again, thanks for your help! -- Mateusz K.