Safe Haskell | Safe-Inferred |
---|---|
Language | Haskell2010 |
Documentation
class (i ~ Index e els) => HGet els e i | els i -> e where Source
Heterogeneous read arbitrarily element from hset
>>>
let x = HSCons (10 :: Int) $ HSCons (20 :: Double) HSNil
>>>
x
HSCons (10) (HSCons (20.0) (HSNil))
>>>
hget x :: Int
10
>>>
hget x :: Double
20.0
Note that hget
takes specific element from list of uniquely typed
elements depending on what type is required to be returned (return
type polymorphism)
type HGettable els e = HGet els e (Index e els) Source
Enables deriving of the fact that e
is contained within els
and it's
safe to say that hget
can be performed on this particular pair.
hgetTagged :: forall proxy label e els. HGettable els (Tagged label e) => proxy label -> HSet els -> e Source
>>>
let y = HSCons (Tagged 10 :: Tagged "x" Int) $ HSCons (Tagged 20 :: Tagged "y" Int) HSNil
>>>
y
HSCons (Tagged 10) (HSCons (Tagged 20) (HSNil))
>>>
hgetTagged (Proxy :: Proxy "x") y :: Int
10
>>>
hgetTagged (Proxy :: Proxy "y") y :: Int
20