| 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
- class (HZipR (MapFst z) (MapSnd z) ~ z) => HUnZip z where
- type family HZipR x y :: [*]
- type family Fst a
- type family Snd a
- hTranspose :: (HZip3 a b c, HFoldr HZipF (HList es) l (HList b), HReplicateFD n (HList ([] *)) es, HLengthEq1 HNat a n, HLengthEq2 HNat a n, SameLength' * * (HReplicateR * n ()) a) => 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
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?
transpose
hTranspose :: (HZip3 a b c, HFoldr HZipF (HList es) l (HList b), HReplicateFD n (HList ([] *)) es, HLengthEq1 HNat a n, HLengthEq2 HNat a n, SameLength' * * (HReplicateR * n ()) a) => 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]]