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

Flipped and infix version of get.

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

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 ...

Sets or updates a field to a value.

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

Infix version of set

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

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 ...

Infix version of modify.

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

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
...

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

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

& 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