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Data.Generics.Reify Portability non-portable Stability experimental Maintainer libraries@haskell.org

Contents Types as values Generic operations to reify terms Generic operations to reify types

Description

"Scrap your boilerplate" --- Generic programming in Haskell See http://www.cs.vu.nl/boilerplate/. The present module provides some preliminary support some sort of structural reflection. This module is presumably less common sense that most other boilerplate modules. Also, it is a bit less easy-going.

Synopsis

type TypeVal a = a -> () typeVal :: TypeVal a sameType :: (Typeable a, Typeable b) => TypeVal a -> TypeVal b -> Bool val2type :: a -> TypeVal a type2val :: TypeVal a -> a withType :: a -> TypeVal a -> a argType :: (a -> b) -> TypeVal a resType :: (a -> b) -> TypeVal b paraType :: t a -> TypeVal a type TypeFun a r = TypeVal a -> r type GTypeFun r = forall a . Data a => TypeFun a r extType :: (Data a, Typeable r) => GTypeFun r -> TypeFun a r -> GTypeFun r glength :: GenericQ Int gcount :: GenericQ Bool -> GenericQ Int gnodecount :: GenericQ Int gtypecount :: Typeable a => (a -> ()) -> GenericQ Int gfindtype :: (Data x, Data y) => x -> Maybe y gmapType :: ([(Constr, r')] -> r) -> GTypeFun (Constr -> r') -> GTypeFun r gmapConstr :: ([r] -> r') -> GTypeFun r -> GTypeFun (Constr -> r') constrArity :: GTypeFun (Constr -> Int) gmapSubtermTypes :: (Data a, Typeable r) => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r gmapSubtermTypesConst :: (Data a, Typeable r) => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r gcountSubtermTypes :: Data a => TypeVal a -> Int reachableType :: (Data a, Data b) => TypeVal a -> TypeVal b -> Bool depthOfType :: GTypeFun Bool -> GTypeFun (Maybe (Constr, Maybe Int)) depthOfConstr :: GTypeFun Bool -> GTypeFun (Constr -> Maybe Int)

Types as values

type TypeVal a = a -> ()

Type as values to stipulate use of undefineds

typeVal :: TypeVal a

The value that denotes a type

sameType :: (Typeable a, Typeable b) => TypeVal a -> TypeVal b -> Bool

Test for type equivalence

val2type :: a -> TypeVal a

Map a value to its type

type2val :: TypeVal a -> a

Stipulate this idiom!

withType :: a -> TypeVal a -> a

Constrain a type

argType :: (a -> b) -> TypeVal a

The argument type of a function

resType :: (a -> b) -> TypeVal b

The result type of a function

paraType :: t a -> TypeVal a

The parameter type of type constructor

type TypeFun a r = TypeVal a -> r

type GTypeFun r = forall a . Data a => TypeFun a r

extType :: (Data a, Typeable r) => GTypeFun r -> TypeFun a r -> GTypeFun r

Extend a type function

Generic operations to reify terms

glength :: GenericQ Int

Count the number of immediate subterms of the given term

gcount :: GenericQ Bool -> GenericQ Int

Determine the number of all suitable nodes in a given term

gnodecount :: GenericQ Int

Determine the number of all nodes in a given term

gtypecount :: Typeable a => (a -> ()) -> GenericQ Int

Determine the number of nodes of a given type in a given term

gfindtype :: (Data x, Data y) => x -> Maybe y

Find (unambiguously) an immediate subterm of a given type

Generic operations to reify types

gmapType :: ([(Constr, r')] -> r) -> GTypeFun (Constr -> r') -> GTypeFun r

Query all constructors of a given type

gmapConstr :: ([r] -> r') -> GTypeFun r -> GTypeFun (Constr -> r')

Query all subterm types of a given constructor

constrArity :: GTypeFun (Constr -> Int)

Compute arity of a given constructor

gmapSubtermTypes :: (Data a, Typeable r) => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r

Query all immediate subterm types of a given type

gmapSubtermTypesConst :: (Data a, Typeable r) => (r -> r -> r) -> r -> GTypeFun r -> TypeVal a -> r

Query all immediate subterm types. There is an extra argument to "constant out" the type at hand. This can be used to avoid cycles.

gcountSubtermTypes :: Data a => TypeVal a -> Int

reachableType :: (Data a, Data b) => TypeVal a -> TypeVal b -> Bool

Reachability relation on types, i.e., test if nodes of type a are reachable from nodes of type b. The relation is defined to be reflexive.

depthOfType :: GTypeFun Bool -> GTypeFun (Maybe (Constr, Maybe Int))

Depth of a datatype as the constructor with the minimum depth. The outermost Nothing denotes a type without constructors. The innermost Nothing denotes potentially infinite.

depthOfConstr :: GTypeFun Bool -> GTypeFun (Constr -> Maybe Int)

Depth of a constructor. Depth is viewed as the maximum depth of all subterm types + 1. Nothing denotes potentially infinite.

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