On 12/21/2012 04:52 AM, Daniel Trstenjak wrote:
Why having a Socket3 in the first place, what's the point of it?
The idea was to have some generic structures (Sockets) which were already instanced into the Monoids-within-Monoids abstraction, yet could still be made concrete into anything more specific. So, I have... code: -------- data Socket3 a b c = Socket3 a b c deriving (Show) instance (Monoid a, Monoid b, Monoid c) => Monoid (Socket3 a b c) where mempty = Socket3 mempty mempty mempty Socket3 a b c `mappend` Socket3 w x y = Socket3 (a <> w) (b <> x) (c <> y) nullSocket3 :: (Monoid a, Monoid b, Monoid c) => Socket3 a b c nullSocket3 = Socket3 mempty mempty mempty -------- ...which allows me to have... code: -------- type ShipSys = Socket3 (Last Engine) (Last RotThruster) [LinThruster] nullShipSys :: ShipSys nullShipSys = nullSocket3 setEngineSocket (Socket3 a b c) x = Socket3 x b c engineSys :: Engine -> ShipSys engineSys a = setEngineSocket nullShipSys (Last (Just a)) mk1Engine = engineSys (Engine 100 1 "Mark I") -- etc. -------- And so, with each individual component being wrapped as a generic ShipSys (ship system), I can make a complete system simply by composition: code: -------- h> :t mk1Engine mk1Engine :: ShipSys h> :t stdRearThruster stdRearThruster :: ShipSys h> :t stdFrontThruster stdFrontThruster :: ShipSys h> :t stdRotThruster stdRotThruster :: Power -> ShipSys h> mk1Engine <> stdRearThruster <> stdFrontThruster <> stdRotThruster 10 Socket3 (Last {getLast = Just (Engine 100.0 1.0 "Mark I")}) (Last {getLast = Just (RotThruster 10.0)}) [LinThruster 3.1415927 1.0,LinThruster 0.0 0.5] -------- This seems to work well enough so far. But the issue I was concerned about is: if I can't layer record syntax onto the type synonym, then I have to rewrite a whole bunch of getters / setters each time I want to add an attribute (e.g., requiring a switch from a Socket3 to a Socket4.) If this is the case, then perhaps it would be better just to define the ShipSys type directly, and directly instance it into the monoid abstraction. -- frigidcode.com