i-am-tom/higgledy
1
1
Fork 0
mirror of https://github.com/i-am-tom/higgledy.git synced 2024-08-17 12:00:27 +03:00
Code Issues Projects Releases Wiki Activity

Merge pull request #16 from i-am-tom/named

Browse Source 
Add named field construction
This commit is contained in:
Tom Harding 2019-10-19 18:09:05 +01:00 committed by GitHub
commit e3b2cc253a
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 162 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

72
README.md
View File

@ -38,7 +38,7 @@ type UserF f = HKD User f
```
As an added little bonus, any `HKD`-wrapped object is automatically an instance
of all the [Barbie](http://hackage.haskell.org/package/barbies) classes, so no
of all the [Barbie](https://hackage.haskell.org/package/barbies) classes, so no
need to derive anything more than `Generic`!
## API
@ -50,6 +50,8 @@ example data types:
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE OverloadedLabels #-}
{-# LANGUAGE TypeOperators #-}
module Main where
import Control.Applicative (Alternative (empty))
@ -61,6 +63,7 @@ import Data.Generic.HKD
import Data.Maybe (isJust, isNothing)
import Data.Monoid (Last (..))
import GHC.Generics (Generic)
import Named ((:!), (!))
-- An example of a record (with named fields):
data User
@ -72,7 +75,7 @@ data User
deriving (Generic, Show)
user :: User
user = User "Tom" 25 True
user = User "Tom" 26 True
-- An example of a product (without named fields):
data Triple
@ -145,7 +148,7 @@ eg3 :: Bare User
eg3 = deconstruct user
-- User
-- { name = Identity "Tom"
-- , age = Identity 25
-- , age = Identity 26
-- , likesDogs = Identity True
-- }
```
@ -184,13 +187,32 @@ eg7 = eg6 [1] [] ["Tom", "Tim"]
-- Triple [1] [] ["Tom","Tim"]
```
Should we need to work with records, we can exploit the label trickery of the
[`named`](https://hackage.haskell.org/package/named) package. The `record`
function behaves exactly as `build` does, but produces a function compatible
with the `named` interface. After that, we can use the function with labels
(and with no regard for the internal order):
```haskell
eg8 :: "name" :! f [Char]
-> "age" :! f Int
-> "likesDogs" :! f Bool
-> HKD User f
eg8 = record @User
eg9 :: HKD User Maybe
eg9 = eg8 ! #name (Just "Tom")
! #likesDogs (Just True)
! #age (Just 26)
```
If you're _still_ not satisfied, check out the
[`buniq`](https://hackage.haskell.org/package/barbies-1.1.2.1/docs/Data-Barbie.html#v:buniq)
method hiding in `barbies`:
```haskell
eg8 :: HKD Triple []
eg8 = buniq empty
eg10 :: HKD Triple []
eg10 = buniq empty
-- Triple [] [] []
```
@ -200,8 +222,8 @@ The `field` lens, when given a type-applied field name, allows us to focus on
fields within a record:
```haskell
eg9 :: Last Int
eg9 = eg0 ^. field @"age"
eg11 :: Last Int
eg11 = eg0 ^. field @"age"
-- Last {getLast = Nothing}
```
@ -210,8 +232,8 @@ record (note that these set values will _also_ need to be in our functor of
choice):
```haskell
eg10 :: Partial User
eg10 = eg0 & field @"name" .~ pure "Evil Tom"
eg12 :: Partial User
eg12 = eg0 & field @"name" .~ pure "Evil Tom"
& field @"likesDogs" .~ pure False
-- User
-- { name = Last {getLast = Just "Evil Tom"}
@ -224,8 +246,8 @@ This also means, for example, we can check whether a particular value has been
completed for a given partial type:
```haskell
eg11 :: Bool
eg11 = anyOf (field @"name") (isJust . getLast) eg0
eg13 :: Bool
eg13 = anyOf (field @"name") (isJust . getLast) eg0
-- False
```
@ -234,8 +256,8 @@ Finally, thanks to the fact that this library exploits some of the internals of
doesn't exist in our type:
```{haskell, ignore}
eg12 :: Identity ()
eg12 = eg3 ^. field @"oops"
eg14 :: Identity ()
eg14 = eg3 ^. field @"oops"
-- error:
-- • The type User does not contain a field named 'oops'.
```
@ -246,8 +268,8 @@ Just as with field names, we can use positions when working with non-record
product types:
```haskell
eg13 :: Labels Triple
eg13 = mempty & position @1 .~ Const "hello"
eg15 :: Labels Triple
eg15 = mempty & position @1 .~ Const "hello"
& position @2 .~ Const "world"
-- Triple
-- Const "hello"
@ -258,11 +280,11 @@ eg13 = mempty & position @1 .~ Const "hello"
Again, this is a `Lens`, so we can just as easily _set_ values:
```haskell
eg14 :: Partial User
eg14 = eg10 & position @2 .~ pure 25
eg16 :: Partial User
eg16 = eg12 & position @2 .~ pure 26
-- User
-- { name = Last {getLast = Just "Evil Tom"}
-- , age = Last {getLast = Just 25}
-- , age = Last {getLast = Just 26}
-- , likesDogs = Last {getLast = Just False}
-- }
```
@ -271,8 +293,8 @@ Similarly, the internals here come to us courtesy of `generic-lens`, so the
type errors are a delight:
```{haskell, ignore}
eg15 :: Identity ()
eg15 = deconstruct @Identity triple ^. position @4
eg17 :: Identity ()
eg17 = deconstruct @Identity triple ^. position @4
-- error:
-- • The type Triple does not contain a field at position 4
```
@ -284,8 +306,8 @@ names of the fields into the functor we're using. The `label` value gives us
this interface:
```haskell
eg16 :: Labels User
eg16 = label
eg18 :: Labels User
eg18 = label
-- User
-- { name = Const "name"
-- , age = Const "age"
@ -294,14 +316,14 @@ eg16 = label
```
By combining this with some of the
[Barbies](http://hackage.haskell.org/package/barbies) interface (the entirety
[Barbies](https://hackage.haskell.org/package/barbies) interface (the entirety
of which is available to any `HKD`-wrapped type) such as `bprod` and `bmap`, we
can implement functions such as `labelsWhere`, which returns the names of all
fields whose values satisfy some predicate:
```haskell
eg17 :: [String]
eg17 = labelsWhere (isNothing . getLast) eg10
eg19 :: [String]
eg19 = labelsWhere (isNothing . getLast) eg12
-- ["age"]
```

3
higgledy.cabal
View File

@ -20,6 +20,7 @@ library
Data.Generic.HKD.Build
Data.Generic.HKD.Construction
Data.Generic.HKD.Labels
Data.Generic.HKD.Named
Data.Generic.HKD.Types
-- other-modules:
-- other-extensions:
@ -27,6 +28,7 @@ library
, barbies ^>= 1.1.0
, generic-lens ^>= 1.1.0
, QuickCheck >= 2.12.6 && < 2.14
, named ^>= 0.3.0.0
hs-source-dirs: src
default-language: Haskell2010
@ -48,6 +50,7 @@ test-suite readme
, barbies ^>= 1.1.0
, lens ^>= 4.17
, higgledy
, named ^>= 0.3.0.0
main-is: README.lhs
type: exitcode-stdio-1.0
default-language: Haskell2010

1
src/Data/Generic/HKD.hs
View File

@ -27,6 +27,7 @@ module Data.Generic.HKD
import Data.Generic.HKD.Build as Exports
import Data.Generic.HKD.Construction as Exports
import Data.Generic.HKD.Labels as Exports
import Data.Generic.HKD.Named as Exports
import Data.Generic.HKD.Types as Exports
import qualified Data.Barbie as Barbie

111
src/Data/Generic/HKD/Named.hs Normal file
View File

@ -0,0 +1,111 @@
{-# OPTIONS_HADDOCK not-home #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
{-|
Module : Data.Generic.HKD.Named
Description : Construct an HKD record with named parameters.
Copyright : (c) Tom Harding, 2019
License : MIT
Maintainer : tom.harding@habito.com
Stability : experimental
-}
module Data.Generic.HKD.Named
( Record (..)
) where
import Data.Functor.Contravariant (Contravariant (..))
import Data.Generic.HKD.Types (HKD, HKD_)
import Data.GenericLens.Internal (GUpcast (..))
import Data.Kind (Type)
import GHC.Generics
import Named ((:!), NamedF (..))
type family Append (xs :: Type -> Type) (ys :: Type -> Type) :: Type -> Type where
Append (S1 meta head) tail = S1 meta head :*: tail
Append (left :*: right) other = left :*: Append right other
type family Rearrange (i :: Type -> Type) :: Type -> Type where
Rearrange (S1 m inner) = S1 m (Rearrange inner)
Rearrange (M1 index m inner) = M1 index m (Rearrange inner)
Rearrange (left :*: right) = Append (Rearrange left) (Rearrange right)
Rearrange (Rec0 inner) = Rec0 inner
-- | The 'Data.Generic.HKD.record' function lets us supply arguments to a type
-- one by one, but can cause confusion when working with a record. If the
-- record contains two fields of the same type, for example, we've introduced
-- an opportunity for bugs and confusion. The @record@ function uses the
-- wonderful @named@ package to help us:
--
-- >>> :set -XDeriveGeneric -XTypeApplications
--
-- >>> :{
-- data User
-- = User { name :: String, enemy :: String }
-- deriving Generic
-- :}
--
-- >>> :{
-- test :: _
-- test = record @User
-- :}
-- ...
-- ... Found type wildcard ...
-- ... standing for ...("name" :! f [Char])
-- ... -> ("enemy" :! f [Char]) -> HKD User f...
-- ...
class Record (structure :: Type) (f :: Type -> Type) (k :: Type)
| f structure -> k where
record :: k
class GRecord (rep :: Type -> Type) (f :: Type -> Type) (structure :: Type) (k :: Type)
| f structure rep -> k where
grecord :: (forall p. rep p -> HKD structure f) -> k
instance GRecord inner f structure k
=> GRecord (D1 meta inner) f structure k where
grecord rebuild = grecord (rebuild . M1)
instance GRecord inner f structure k
=> GRecord (C1 meta inner) f structure k where
grecord rebuild = grecord (rebuild . M1)
instance
( rec ~ (Rec0 inner)
, k ~ (name :! inner -> HKD structure f)
, meta ~ 'MetaSel ('Just name) i d c
)
=> GRecord (S1 meta rec) f structure k where
grecord fill = \(Arg inner) -> fill (M1 (K1 inner))
instance
( GRecord right f structure k'
, rec ~ Rec0 x
, left ~ S1 ('MetaSel ('Just name) i d c) rec
, k ~ (name :! x -> k')
)
=> GRecord (left :*: right) f structure k where
grecord fill = \(Arg left) -> grecord \right -> fill (M1 (K1 left) :*: right)
instance
( Contravariant (HKD_ f structure)
, Functor (HKD_ f structure)
, list ~ Rearrange (HKD_ f structure)
, GUpcast list (HKD_ f structure)
, GRecord list f structure k
)
=> Record structure f k where
record = grecord @_ @f @structure (to . gupcast @list @(HKD_ f structure))