Bookkeeper

Preamble

The examples here presume the following setup:

>>> import Data.Char (toUpper)
>>> type Person = Book '[ "name" :=> String , "age" :=> Int ]
>>> let julian :: Person = emptyBook & #age =: 28 & #name =: "Julian K. Arni"

The OverloadedLabels and TypeOperators extensions are also required.

A word of warning: The signatures for most of the functions are quite arcane, even though their behaviour is intuitive.

Initialization

emptyBook :: Book '[]

A book with no records. You'll usually want to use this to construct books.

Getters

(?:) :: forall field book val. (Submap '[field :=> val] book, Contains book field val) => Book' book -> Key field -> val infixl 3

Flipped and infix version of get.

>>> julian ?: #name
"Julian K. Arni"

get :: forall field book val. (Submap '[field :=> val] book, Contains book field val) => Key field -> Book' book -> val

Get a value by key, if it exists.

>>> get #age julian
28

If the key does not exist, throws a type error >>> get #moneyFrom julian ... ... • The provided Book does not contain the field "moneyFrom" ... Book type: ... '["age" ':-> Int, "name" ':-> String] ... • In the expression: get #moneyFrom julian ...

Setters

set :: forall field val old mid1 mid2 new. (Unionable '[field :=> ChooseFirst val] mid1, Mappable ChooseFirst old mid1, Mappable ChooseFirst new mid2, mid1 ~ MapThere ChooseFirst old, mid2 ~ Union '[field :=> ChooseFirst val] mid1, new ~ MapBack ChooseFirst mid2) => Key field -> val -> Book' old -> Book' new

Sets or updates a field to a value.

>>> let julian' = set #likesDoctest True julian
>>> get #likesDoctest julian'
True

(=:) :: forall field val old mid1 mid2 new. (Unionable '[field :=> ChooseFirst val] mid1, Mappable ChooseFirst old mid1, Mappable ChooseFirst new mid2, mid1 ~ MapThere ChooseFirst old, mid2 ~ Union '[field :=> ChooseFirst val] mid1, new ~ MapBack ChooseFirst mid2) => Key field -> val -> Book' old -> Book' new infix 3

Infix version of set

>>> let julian' = julian & #age =: 29
>>> get #age julian'
29

Modifying

modify :: forall field val val' old mid1 mid2 new. (Unionable '[field :=> ChooseFirst val'] mid1, Mappable ChooseFirst old mid1, Mappable ChooseFirst new mid2, (Submap '[field :=> val] old, Contains old field val), mid1 ~ MapThere ChooseFirst old, mid2 ~ Union '[field :=> ChooseFirst val'] mid1, new ~ MapBack ChooseFirst mid2, AsMap new ~ new) => Key field -> (val -> val') -> Book' old -> Book new

Apply a function to a field.

>>> let julian' = julian & modify #name (fmap toUpper)
>>> get #name julian'
"JULIAN K. ARNI"

If the key does not exist, throws a type error >>> modify #height (_ -> 132) julian ... ... • The provided Book does not contain the field "height" ... Book type: ... '["age" ':-> Int, "name" ':-> String] ... • In the expression: modify #height ( _ -> 132) julian ...

(%:) :: forall field val val' old mid1 mid2 new. (Unionable '[field :=> ChooseFirst val'] mid1, Mappable ChooseFirst old mid1, Mappable ChooseFirst new mid2, (Submap '[field :=> val] old, Contains old field val), mid1 ~ MapThere ChooseFirst old, mid2 ~ Union '[field :=> ChooseFirst val'] mid1, new ~ MapBack ChooseFirst mid2, AsMap new ~ new) => Key field -> (val -> val') -> Book' old -> Book new infixr 3

Infix version of modify.

>>> let julian' = julian & #name %: fmap toUpper
>>> get #name julian'
"JULIAN K. ARNI"

Deleting

delete :: forall field old. Submap (AsMap (old :\ field)) old => Key field -> Book' old -> Book (old :\ field)

Delete a field from a Book, if it exists. If it does not, returns the Book unmodified.

>>> get #name $ delete #name julian
...
...  • The provided Book does not contain the field "name"
...    Book type:
...    '["age" ':-> Int]
...  • In the expression: get #name
...

Types

type Book a = Book' (AsMap a)

type (:=>) a b = a :-> b

An alias for :-> because otherwise you'll have to tick your constructors.

data Key a

Key is simply a proxy. You will usually not need to generate it directly, as it is generated by the OverlodadedLabels magic.

Instances

(~) Symbol s s' => IsLabel s (Key s')

Methods

fromLabel :: Proxy# Symbol s -> Key s'

Eq (Key a)

Methods

(==) :: Key a -> Key a -> Bool

(/=) :: Key a -> Key a -> Bool

Read (Key a)

Methods

readsPrec :: Int -> ReadS (Key a)

readList :: ReadS [Key a]

readPrec :: ReadPrec (Key a)

readListPrec :: ReadPrec [Key a]

Show (Key a)

Methods

showsPrec :: Int -> Key a -> ShowS

show :: Key a -> String

showList :: [Key a] -> ShowS

Generic (Key a)

Associated Types

type Rep (Key a) :: * -> *

Methods

from :: Key a -> Rep (Key a) x

to :: Rep (Key a) x -> Key a

type Rep (Key a)

type Rep (Key a) = D1 (MetaData "Key" "Bookkeeper.Internal" "bookkeeper-0.1.1.0-ICAKLsZPqBcAB7K0G53i1T" False) (C1 (MetaCons "Key" PrefixI False) U1)

Re-exports

(&) :: a -> (a -> b) -> b infixl 1

& is a reverse application operator. This provides notational convenience. Its precedence is one higher than that of the forward application operator $, which allows & to be nested in $.

Since: 4.8.0.0

For coercion

These types should not be used, but need to be in scope for coercion, which is used when setting or modifying a value.

newtype ChooseFirst a

Warning: This should not be used

Constructors

ChooseFirst

Warning: This should not be used

Fields

• getChooseFirst :: a

Instances

Eq a => Eq (ChooseFirst a)

Methods

(==) :: ChooseFirst a -> ChooseFirst a -> Bool

(/=) :: ChooseFirst a -> ChooseFirst a -> Bool

Read a => Read (ChooseFirst a)

Methods

readsPrec :: Int -> ReadS (ChooseFirst a)

readList :: ReadS [ChooseFirst a]

readPrec :: ReadPrec (ChooseFirst a)

readListPrec :: ReadPrec [ChooseFirst a]

Show a => Show (ChooseFirst a)

Methods

showsPrec :: Int -> ChooseFirst a -> ShowS

show :: ChooseFirst a -> String

showList :: [ChooseFirst a] -> ShowS

Generic (ChooseFirst a)

Associated Types

type Rep (ChooseFirst a) :: * -> *

Methods

from :: ChooseFirst a -> Rep (ChooseFirst a) x

to :: Rep (ChooseFirst a) x -> ChooseFirst a

Combinable (ChooseFirst a) (ChooseFirst b)

Methods

combine :: ChooseFirst a -> ChooseFirst b -> Combine * (ChooseFirst a) (ChooseFirst b)

type Rep (ChooseFirst a)

type Rep (ChooseFirst a) = D1 (MetaData "ChooseFirst" "Bookkeeper.Internal" "bookkeeper-0.1.1.0-ICAKLsZPqBcAB7K0G53i1T" True) (C1 (MetaCons "ChooseFirst" PrefixI True) (S1 (MetaSel (Just Symbol "getChooseFirst") NoSourceUnpackedness NoSourceStrictness DecidedLazy) (Rec0 a)))

type Combine * (ChooseFirst a) (ChooseFirst b)

type Combine * (ChooseFirst a) (ChooseFirst b) = ChooseFirst a