multirec-0.2: Generic programming with systems of recursive datatypes Source code Contents Index

Generics.MultiRec.Base Portability non-portable Stability experimental Maintainer generics@haskell.org

Contents Structure types Constructor information Unlifted variants Indexed systems

Description

This module is the base of the multirec library. It defines the view of a system of datatypes: All the datatypes of the system are represented as indexed functors that are built up from the structure types defined in this module. Furthermore, in order to use the library for a system, conversion functions have to be defined between the original datatypes and their representation. The type class that holds these conversion functions are also defined here.

Synopsis

data I where I :: Ix s xi => r xi -> I xi s r ix unI :: I xi s r ix -> r xi data K a s r ix = K { unK :: a } data U s r ix = U data (f :+: g) s r ix = L (f s r ix) | R (g s r ix) data (f :*: g) s r ix = (f s r ix) :*: (g s r ix) data :>: where Tag :: f s r ix -> (f :>: ix) s r ix unTag :: (f :>: ix) s r ix -> f s r ix data C c f s r ix where C :: Constructor c => f s r ix -> C c f s r ix unC :: C c f s r ix -> f s r ix module Generics.MultiRec.Constructor newtype I0 a = I0 { unI0 :: a } newtype K0 a b = K0 { unK0 :: a } type family PF s :: (* -> *) -> (* -> *) -> * -> * type Str s ix = PF s s I0 ix class Ix s ix where from_ :: ix -> Str s ix to_ :: Str s ix -> ix from :: pfs ~ PF s => ix -> pfs s I0 ix to :: pfs ~ PF s => pfs s I0 ix -> ix index :: s ix

Structure types

data I where Source

Represents recursive positions. The first argument indicates which type (within the system) to recurse on. Constructors I :: Ix s xi => r xi -> I xi s r ix Instances ConNames (I a) HFunctor (I xi) Fold (I xi) Fold (I xi) HEq (I xi) HShow (I xi)

unI :: I xi s r ix -> r xi Source

Destructor for I.

data K a s r ix Source

Represents constant types that do not belong to the system. Constructors K unK :: a Instances ConNames (K x) HFunctor (K x) Fold (K a) Fold (K a) Eq x => HEq (K x) Show x => HShow (K x)

data U s r ix Source

Represents constructors without fields. Constructors U Instances ConNames U HFunctor U Fold U Fold U HEq U HShow U

data (f :+: g) s r ix Source

Represents sums (choices between constructors). Constructors L (f s r ix) R (g s r ix) Instances (ConNames f, ConNames g) => ConNames (f :+: g) (HFunctor f, HFunctor g) => HFunctor (f :+: g) (Fold f, Fold g) => Fold (f :+: g) (Fold f, Fold g) => Fold (f :+: g) (HEq f, HEq g) => HEq (f :+: g) (HShow f, HShow g) => HShow (f :+: g)

data (f :*: g) s r ix Source

Represents products (sequences of fields of a constructor). Constructors (f s r ix) :*: (g s r ix) Instances ConNames (f :*: g) (HFunctor f, HFunctor g) => HFunctor (f :*: g) Fold g => Fold (K a :*: g) Fold g => Fold (I xi :*: g) Fold g => Fold (K a :*: g) Fold g => Fold (I xi :*: g) (HEq f, HEq g) => HEq (f :*: g) (HShow f, HShow g) => HShow (f :*: g)

data :>: where Source

Is used to indicate the type (within the system) that a particular constructor injects to. Constructors Tag :: f s r ix -> (f :>: ix) s r ix Instances ConNames f => ConNames (f :>: ix) HFunctor f => HFunctor (f :>: ix) Fold f => Fold (f :>: xi) Fold f => Fold (f :>: xi) HEq f => HEq (f :>: ix) HShow f => HShow (f :>: ix)

unTag :: (f :>: ix) s r ix -> f s r ix Source

Destructor for '(:>:)'.

data C c f s r ix where Source

Represents constructors. Constructors C :: Constructor c => f s r ix -> C c f s r ix Instances Constructor c => ConNames (C c f) HFunctor f => HFunctor (C c f) Fold f => Fold (C c f) Fold f => Fold (C c f) HEq f => HEq (C c f) HShow f => HShow (C c f)

unC :: C c f s r ix -> f s r ix Source

Destructor for C.

Constructor information

module Generics.MultiRec.Constructor

Unlifted variants

newtype I0 a Source

Unlifted version of I. Constructors I0 unI0 :: a Instances Functor I0 Applicative I0

newtype K0 a b Source

Unlifted version of K. Constructors K0 unK0 :: a Instances Functor (K0 a)

Indexed systems

type family PF s :: (* -> *) -> (* -> *) -> * -> * Source

Type family describing the pattern functor of a system.

type Str s ix = PF s s I0 ix Source

class Ix s ix where Source

Methods from_ :: ix -> Str s ix Source to_ :: Str s ix -> ix Source from :: pfs ~ PF s => ix -> pfs s I0 ix Source Some functions need to have their types desugared in order to make programs that use them typable. Desugaring consists in transforming `inline' type family applications into equality constraints. This is a strangeness in current versions of GHC that hopefully will be fixed sometime in the future. to :: pfs ~ PF s => pfs s I0 ix -> ix Source index :: s ix Source

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