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Add buniq to README

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It's another perfectly legitimate way to construct an object!
This commit is contained in:
Tom Harding 2019-06-24 09:01:47 +01:00
parent 9c7b830bdc
commit 94171f3401
1 changed files with 31 additions and 19 deletions
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@ -52,7 +52,9 @@ example data types:
{-# LANGUAGE TypeApplications #-}
module Main where
import Control.Applicative (Alternative (empty))
import Control.Lens ((.~), (^.), (&), Const (..), Identity, anyOf)
import Data.Barbie (ProductB (buniq))
import Data.Functor.Const (Const (..))
import Data.Functor.Identity (Identity (..))
import Data.Generic.HKD
@ -178,14 +180,24 @@ eg7 = eg6 [1] [] ["Tom", "Tim"]
-- Triple [1] [] ["Tom","Tim"]
```
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
-- Triple [] [] []
```
### Field Access
The `field` lens, when given a type-applied field name, allows us to focus on
fields within a record:
```haskell
eg8 :: Last Int
eg8 = eg0 ^. field @"age"
eg9 :: Last Int
eg9 = eg0 ^. field @"age"
-- Last {getLast = Nothing}
```
@ -194,9 +206,9 @@ record (note that these set values will _also_ need to be in our functor of
choice):
```haskell
eg9 :: Partial User
eg9 = eg0 & field @"name" .~ pure "Evil Tom"
& field @"likesDogs" .~ pure False
eg10 :: Partial User
eg10 = eg0 & field @"name" .~ pure "Evil Tom"
& field @"likesDogs" .~ pure False
-- User
-- { name = Last {getLast = Just "Evil Tom"}
-- , age = Last {getLast = Nothing}
@ -208,8 +220,8 @@ This also means, for example, we can check whether a particular value has been
completed for a given partial type:
```haskell
eg10 :: Bool
eg10 = anyOf (field @"name") (isJust . getLast) eg0
eg11 :: Bool
eg11 = anyOf (field @"name") (isJust . getLast) eg0
-- False
```
@ -218,8 +230,8 @@ Finally, thanks to the fact that this library exploits some of the internals of
doesn't exist in our type:
```{haskell, ignore}
eg11 :: Identity ()
eg11 = eg3 ^. field @"oops"
eg12 :: Identity ()
eg12 = eg3 ^. field @"oops"
-- error:
-- • The type User does not contain a field named 'oops'.
```
@ -230,8 +242,8 @@ Just as with field names, we can use positions when working with non-record
product types:
```haskell
eg12 :: Labels Triple
eg12 = mempty & position @1 .~ Const "hello"
eg13 :: Labels Triple
eg13 = mempty & position @1 .~ Const "hello"
& position @2 .~ Const "world"
-- Triple
-- Const "hello"
@ -242,8 +254,8 @@ eg12 = mempty & position @1 .~ Const "hello"
Again, this is a `Lens`, so we can just as easily _set_ values:
```haskell
eg13 :: Partial User
eg13 = eg9 & position @2 .~ pure 25
eg14 :: Partial User
eg14 = eg10 & position @2 .~ pure 25
-- User
-- { name = Last {getLast = Just "Evil Tom"}
-- , age = Last {getLast = Just 25}
@ -255,8 +267,8 @@ Similarly, the internals here come to us courtesy of `generic-lens`, so the
type errors are a delight:
```{haskell, ignore}
eg14 :: Identity ()
eg14 = deconstruct @Identity triple ^. position @4
eg15 :: Identity ()
eg15 = deconstruct @Identity triple ^. position @4
-- error:
-- • The type Triple does not contain a field at position 4
```
@ -268,8 +280,8 @@ names of the fields into the functor we're using. The `label` value gives us
this interface:
```haskell
eg15 :: Labels User
eg15 = label
eg16 :: Labels User
eg16 = label
-- User
-- { name = Const "name"
-- , age = Const "age"
@ -284,8 +296,8 @@ can implement functions such as `labelsWhere`, which returns the names of all
fields whose values satisfy some predicate:
```haskell
eg16 :: [String]
eg16 = labelsWhere (isNothing . getLast) eg9
eg17 :: [String]
eg17 = labelsWhere (isNothing . getLast) eg10
-- ["age"]
```