| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Data.HList.HZip
Description
The HList library
(C) 2004, Oleg Kiselyov, Ralf Laemmel, Keean Schupke
Zipping and unzipping for (conceptually) lists of pairs.
Provides two alternative implementations
Synopsis
- class HZipR (MapFst z) (MapSnd z) ~ z => HUnZip z where
- type family HZipR (x :: [*]) (y :: [*]) :: [*]
- type family Fst a
- type family Snd a
- hTranspose :: forall (a :: [Type]) (b :: [Type]) (c :: [Type]) (es :: [Type]) (l :: [Type]) (n :: HNat). (HZip3 a b c, HFoldr HZipF (HList es) l (HList b), HReplicateFD n (HList ('[] :: [Type])) es, SameLength' (HReplicateR n ()) a, HLengthEq1 a n, HLengthEq2 a n) => HList (HList a ': l) -> HList c
- class HZip3 x y l | x y -> l, l -> x y where
- data HZipF = HZipF
zip
functional dependency
moved to Data.HList.HList to avoid an orphan instance
type family
hZip2 can be written as a standalone function, with an appropriate
type family to calculate the result type. However, that does not seem to
be the case for hUnzip2, so to re-use some type functions the two are
in the same class.
class HZipR (MapFst z) (MapSnd z) ~ z => HUnZip z where Source #
HZipR in the superclass constraint doesn't hurt, but it doesn't seem to be necessary
Methods
hZip2 :: HList (MapFst z) -> HList (MapSnd z) -> HList z Source #
hUnzip2 :: HList z -> (HList (MapFst z), HList (MapSnd z)) Source #
type family HZipR (x :: [*]) (y :: [*]) :: [*] Source #
calculates something like:
[a] -> [b] -> [(a,b)]
can be used to give another type for hZip2
hZip2 :: HList a -> HList b -> HList (HZipR a b)
utility type functions
do they belong somewhere else?
Instances
| type Fst (a, b) Source # | |
Defined in Data.HList.HZip type Fst (a, b) = a | |
Instances
| type Snd (a, b) Source # | |
Defined in Data.HList.HZip type Snd (a, b) = b | |
transpose
hTranspose :: forall (a :: [Type]) (b :: [Type]) (c :: [Type]) (es :: [Type]) (l :: [Type]) (n :: HNat). (HZip3 a b c, HFoldr HZipF (HList es) l (HList b), HReplicateFD n (HList ('[] :: [Type])) es, SameLength' (HReplicateR n ()) a, HLengthEq1 a n, HLengthEq2 a n) => HList (HList a ': l) -> HList c Source #
this transpose requires equal-length HLists inside a HList:
>>>import Data.HList.HListPrelude>>>let ex = (1 .*. 2 .*. HNil) .*. ('a' .*. 'b' .*. HNil) .*. ( 3 .*. 5 .*. HNil) .*. HNil
The original list:
>>>exH[H[1,2],H['a','b'],H[3,5]]
And transposed:
>>>hTranspose exH[H[1,'a',3],H[2,'b',5]]
helpers
class HZip3 x y l | x y -> l, l -> x y where Source #
same as HZip but HCons the elements of x onto y. This might be doable as
a hMap f (hZip x y), but that one doesn't propagate types as easily it
seems.