Generics.SOP.Skeleton

Generic computation of a skeleton.

Documentation

A skeleton for a record type has a defined "spine" but is undefined everywhere else. For instance, a skeleton for pairs would be

(undefined, undefined)

class Skeleton a where

Generic computation of a skeleton.

A skeleton for a record type has a defined "spine" but is undefined everywhere else. For instance, a skeleton for pairs would be

(undefined, undefined)

We introduce a type class for this purpose because the skeleton for nested records would look like

(undefined, (undefined, undefined))

The default instance of skeleton applies to record types; for everything else, use undefined (or error):

instance Skeleton SomeRecordType -- no where clause

or

instance Skeleton SomeNonRecordType where skeleton = undefined

This is an example of how SOP-style generic functions can be used with DefaultSignatures.

Furthermore, metadata is used in order to produce better error messages. For the undefined components of a record, an error is triggered that mentions the name of the field.

Minimal complete definition

Nothing

Methods

skeleton :: (Generic a, HasDatatypeInfo a, Code a ~ '[xs], All Skeleton xs) => a

Returns a skeleton.

skeleton :: a

Returns a skeleton.

Instances

Skeleton Bool

Defined in Generics.SOP.Skeleton

Methods

skeleton :: Bool

Skeleton Double

Defined in Generics.SOP.Skeleton

Methods

skeleton :: Double

Skeleton Int

Defined in Generics.SOP.Skeleton

Methods

skeleton :: Int

Skeleton Rational

Defined in Generics.SOP.Skeleton

Methods

skeleton :: Rational

Skeleton Text

Defined in Generics.SOP.Skeleton

Methods

skeleton :: Text

Skeleton [a]

Defined in Generics.SOP.Skeleton

Methods

skeleton :: [a]

Skeleton (Maybe a)

Defined in Generics.SOP.Skeleton

Methods

skeleton :: Maybe a