This function is already in the HList library (well early versions
anyway)... I dont think
this is in the current distribution. Its a generic constructor
wrapper. For example:
hMarkAll Just hlist
class HList l => HMarkAll c l m | c l -> m where
hMarkAll :: (forall a . a -> c a) -> l -> m
instance HMarkAll c HNil HNil where
hMarkAll _ _ = HNil
instance HMarkAll c l m => HMarkAll c (HCons e l) (HCons (c e) m) where
hMarkAll c (HCons e l) = HCons (c e) (hMarkAll c l)
Keean.
Joel Reymont wrote:
Credit goes to Cale:
class (HList l, HList p) => HLPU p l | p -> l, l -> p where
puHList :: p -> PU l
instance HLPU HNil HNil where
puHList HNil = lift HNil
instance (HList l, HLPU p l) => HLPU (HCons (PU e) p) (HCons e l) where
puHList (HCons pe l) =
wrap (\(a, b) -> HCons a b,
\(HCons a b) -> (a, b))
(pair pe (puHList l))
On Nov 10, 2005, at 2:04 PM, Joel Reymont wrote:
Folks,
I'm having trouble creating a pickler for HLists and would
appreciate a solution.
The code for (HCons e HNil) works fine but I get an error trying to
implement puHList for (HCons e l) where l is supposed to be (HCons e
...), i.e. another HList.
Bar.hs:21:37:
Couldn't match the rigid variable e' against PU e'
`e' is bound by the instance declaration at Bar.hs:17:0
Expected type: HCons (PU e) l Inferred type: HCons e l
In the first argument of puHList', namely l'
In the second argument of pair', namely (puHList l)'
Failed, modules loaded: none.
--
http://wagerlabs.com/
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