Data.HSet.Get

Documentation

class (i ~ IndexOf e els) => HGet els e i | els i -> e where

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)

Methods

hget :: HSet els -> e

Gets any data from HSet for you

Instances

HGet ((:) * e els) e Z

((~) N (S i) (IndexOf * e ((:) * e1 els)), HGet els e i) => HGet ((:) * e1 els) e (S i)

type HGettable els e = HGet els e (IndexOf e els)

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.

type family AllHGettable els subels :: Constraint

Reduces to (HGettable els e1, HGettable els e2, ..)

Equations

AllHGettable els `[]` = ()

AllHGettable els (e : subels) = (HGettable els e, AllHGettable els subels)

hgetTagged :: forall proxy label e els. HGettable els (Tagged label e) => proxy label -> HSet els -> e

>>> 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