| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Bookkeeper
- emptyBook :: Book '[]
- type Gettable field book val = (Submap '[field :=> val] book, Contains book field val)
- (?:) :: forall field book val. Gettable field book val => Book' book -> Key field -> val
- get :: forall field book val. Gettable field book val => Key field -> Book' book -> val
- type Settable field val old new = (Submap (AsMap (old :\ field)) old, Unionable '[field :=> val] (AsMap (old :\ field)), new ~ AsMap ((field :=> val) ': AsMap (old :\ field)))
- set :: forall field val old new. Settable field val old new => Key field -> val -> Book' old -> Book' new
- (=:) :: Settable field val old new => Key field -> val -> Book' old -> Book' new
- type Modifiable field val val' old new = (Settable field val' old new, AsMap new ~ new, Contains old field val, Submap '[field :=> val] old)
- modify :: Modifiable field val val' old new => Key field -> (val -> val') -> Book' old -> Book new
- (%:) :: Modifiable field val val' old new => Key field -> (val -> val') -> Book' old -> Book new
- delete :: forall field old. Submap (AsMap (old :\ field)) old => Key field -> Book' old -> Book (old :\ field)
- type Book a = Book' (AsMap a)
- type (:=>) a b = a :-> b
- data Key (a :: Symbol)
- fromRecord :: (Generic a, FromGeneric (Rep a) bookRep) => a -> Book' bookRep
- (&) :: a -> (a -> b) -> b
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 '[] Source #
A book with no records. You'll usually want to use this to construct books.
Getters
type Gettable field book val = (Submap '[field :=> val] book, Contains book field val) Source #
Gettable field val book is the constraint needed to get a value of type
val from the field field in the book of type Book book.
(?:) :: forall field book val. Gettable field book val => Book' book -> Key field -> val infixl 3 Source #
Flipped and infix version of get.
>>>julian ?: #name"Julian K. Arni"
get :: forall field book val. Gettable field book val => Key field -> Book' book -> val Source #
Get a value by key, if it exists.
>>>get #age julian28
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
type Settable field val old new = (Submap (AsMap (old :\ field)) old, Unionable '[field :=> val] (AsMap (old :\ field)), new ~ AsMap ((field :=> val) ': AsMap (old :\ field))) Source #
'Settable field val old new' is a constraint needed to set the the field
field to a value of type val in the book of type 'Book old'. The
resulting book will have type 'Book new'.
set :: forall field val old new. Settable field val old new => Key field -> val -> Book' old -> Book' new Source #
Sets or updates a field to a value.
>>>set #likesDoctest True julianBook {age = 28, likesDoctest = True, name = "Julian K. Arni"}
(=:) :: Settable field val old new => Key field -> val -> Book' old -> Book' new infix 3 Source #
Infix version of set
>>>julian & #age =: 29Book {age = 29, name = "Julian K. Arni"}
Modifying
type Modifiable field val val' old new = (Settable field val' old new, AsMap new ~ new, Contains old field val, Submap '[field :=> val] old) Source #
Modifiable field val val' old new is a constraint needed to apply a
function of type val -> val' to the field field in the book of type
Book old. The resulting book will have type Book new.
modify :: Modifiable field val val' old new => Key field -> (val -> val') -> Book' old -> Book new Source #
Apply a function to a field.
>>>julian & modify #name (fmap toUpper)Book {age = 28, name = "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 ...
(%:) :: Modifiable field val val' old new => Key field -> (val -> val') -> Book' old -> Book new infixr 3 Source #
Infix version of modify.
>>>julian & #name %: fmap toUpperBook {age = 28, name = "JULIAN K. ARNI"}
Deleting
delete :: forall field old. Submap (AsMap (old :\ field)) old => Key field -> Book' old -> Book (old :\ field) Source #
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 (:=>) a b = a :-> b Source #
An alias for :-> because otherwise you'll have to tick your
constructors.
data Key (a :: Symbol) Source #
Key is simply a proxy. You will usually not need to generate it
directly, as it is generated by the OverlodadedLabels magic.
From Haskell record
fromRecord :: (Generic a, FromGeneric (Rep a) bookRep) => a -> Book' bookRep Source #
Generate a Book from an ordinary Haskell record via GHC Generics.
>>>data Test = Test { field1 :: String, field2 :: Int, field3 :: Char } deriving Generic>>>fromRecord (Test "hello" 0 'c')Book {field1 = "hello", field2 = 0, field3 = 'c'}
Trying to convert a datatype which is not a record will result in a type error:
>>>data SomeSumType = LeftSide | RightSide deriving Generic>>>fromRecord LeftSide... ... • Cannot convert sum types into Books ...
>>>data Unit = Unit deriving Generic>>>fromRecord Unit... ... • Cannot convert non-record types into Books ...