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append and split NP #115

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append and split NP #115

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05ceba5
append and split NP
Feb 4, 2020
554b070
export type
Feb 5, 2020
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31 changes: 30 additions & 1 deletion sop-core/src/Data/SOP/NP.hs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,9 @@
{-# LANGUAGE PolyKinds, StandaloneDeriving, UndecidableInstances #-}
{-# LANGUAGE
PolyKinds
, StandaloneDeriving
, TypeApplications
, UndecidableInstances
#-}
-- | n-ary products (and products of products)
module Data.SOP.NP
( -- * Datatypes
Expand All @@ -10,6 +15,8 @@ module Data.SOP.NP
, pure_POP
, cpure_NP
, cpure_POP
, type (++)
, happend
-- ** Construction from a list
, fromList
-- * Application
Expand All @@ -21,6 +28,7 @@ module Data.SOP.NP
, Projection
, projections
, shiftProjection
, hsplit
-- * Lifting / mapping
, liftA_NP
, liftA_POP
Expand Down Expand Up @@ -273,6 +281,17 @@ instance HPure POP where
hpure = pure_POP
hcpure = cpure_POP

-- | Append type level lists with `++` type operator.
type family (++) xs ys where
'[] ++ ys = ys
(x ': xs) ++ ys = x ': (xs ++ ys)
infixr 5 ++

-- | Append n-ary products with `happend`.
happend :: NP f xs -> NP f ys -> NP f (xs ++ ys)
happend Nil ys = ys
happend (x :* xs) ys = x :* happend xs ys

-- ** Construction from a list

-- | Construct a homogeneous n-ary product from a normal Haskell list.
Expand Down Expand Up @@ -360,6 +379,16 @@ projections = case sList :: SList xs of
shiftProjection :: Projection f xs a -> Projection f (x ': xs) a
shiftProjection (Fn f) = Fn $ f . K . tl . unK

-- | Split an n-ary product with `hsplit`.
hsplit
:: forall xs ys f. SListI xs
=> NP f (xs ++ ys)
-> (NP f xs, NP f ys)
hsplit = case sList @xs of
SNil -> \ys -> (Nil, ys)
SCons -> \(x :* xsys) ->
case hsplit xsys of (xs,ys) -> (x :* xs, ys)

-- * Lifting / mapping

-- | Specialization of 'hliftA'.
Expand Down