Data.GI.Base.Overloading

Helpers for dealing with overladed properties, signals and methods.

Type level inheritance

type family ParentTypes a :: [*]

All the types that are ascendants of this type, including interfaces that the type implements.

class HasParentTypes (o :: *)

A constraint on a type, to be fulfilled whenever it has a type instance for ParentTypes. This leads to nicer errors, thanks to the overlappable instance below.

Instances

(TypeError (('Text "Type \8216" :<>: 'ShowType a) :<>: 'Text "\8217 does not have any known parent types.") :: Constraint) => HasParentTypes a

Default instance, which will give rise to an error for types without an associated ParentTypes instance.

Defined in Data.GI.Base.Overloading

type family IsDescendantOf (parent :: *) (descendant :: *) :: Constraint where ...

Check that a type is in the list of ParentTypes of another type.

Equations

IsDescendantOf d d = ()

IsDescendantOf p d = CheckForAncestorType d p (ParentTypes d)

asA :: (ManagedPtrNewtype a, ManagedPtrNewtype b, HasParentTypes b, IsDescendantOf a b) => b -> (ManagedPtr a -> a) -> a

Safe coercions to a parent class. For instance:

#show $ label `asA` Gtk.Widget

Looking up attributes in parent types

type family AttributeList a :: [(Symbol, *)]

The list of attributes defined for a given type. Each element of the list is a tuple, with the first element of the tuple the name of the attribute, and the second the type encoding the information of the attribute. This type will be an instance of AttrInfo.

class HasAttributeList a

A constraint on a type, to be fulfilled whenever it has a type instance for AttributeList. This is here for nicer error reporting.

Instances

(TypeError (('Text "Type \8216" :<>: 'ShowType a) :<>: 'Text "\8217 does not have any known attributes.") :: Constraint) => HasAttributeList (a :: k)

Default instance, which will give rise to an error for types without an associated AttributeList.

Defined in Data.GI.Base.Overloading

type family ResolveAttribute (s :: Symbol) (o :: *) :: * where ...

Return the type encoding the attribute information for a given type and attribute.

Equations

ResolveAttribute s o = FindElement s (AttributeList o) (((('Text "Unknown attribute \8216" :<>: 'Text s) :<>: 'Text "\8217 for object \8216") :<>: 'ShowType o) :<>: 'Text "\8217.")

type family HasAttribute (attr :: Symbol) (o :: *) :: Constraint where ...

A constraint imposing that the given object has the given attribute.

Equations

HasAttribute attr o = IsElem attr (AttributeList o) (() :: Constraint) (((('Text "Attribute \8216" :<>: 'Text attr) :<>: 'Text "\8217 not found for type \8216") :<>: 'ShowType o) :<>: 'Text "\8217.")

class HasAttr (attr :: Symbol) (o :: *)

A constraint that enforces that the given type has a given attribute.

Instances

HasAttribute attr o => HasAttr attr o

Defined in Data.GI.Base.Overloading

Looking up signals in parent types

type family SignalList a :: [(Symbol, *)]

The list of signals defined for a given type. Each element of the list is a tuple, with the first element of the tuple the name of the signal, and the second the type encoding the information of the signal. This type will be an instance of SignalInfo.

type family ResolveSignal (s :: Symbol) (o :: *) :: * where ...

Return the type encoding the signal information for a given type and signal.

Equations

ResolveSignal s o = FindElement s (SignalList o) (((('Text "Unknown signal \8216" :<>: 'Text s) :<>: 'Text "\8217 for object \8216") :<>: 'ShowType o) :<>: 'Text "\8217.")

type family HasSignal (s :: Symbol) (o :: *) :: Constraint where ...

A constraint enforcing that the signal exists for the given object, or one of its ancestors.

Equations

HasSignal s o = IsElem s (SignalList o) (() :: Constraint) (((('Text "Signal \8216" :<>: 'Text s) :<>: 'Text "\8217 not found for type \8216") :<>: 'ShowType o) :<>: 'Text "\8217.")

Looking up methods in parent types

type family MethodResolutionFailed (method :: Symbol) (o :: *) where ...

Returned when the method is not found, hopefully making the resulting error messages somewhat clearer.

Equations

MethodResolutionFailed m o = TypeError (((('Text "Unknown method \8216" :<>: 'Text m) :<>: 'Text "\8217 for type \8216") :<>: 'ShowType o) :<>: 'Text "\8217.")

type family UnsupportedMethodError (s :: Symbol) (o :: *) :: * where ...

A constraint that always fails with a type error, for documentation purposes.

Equations

UnsupportedMethodError s o = TypeError (((('Text "Unsupported method \8216" :<>: 'Text s) :<>: 'Text "\8217 for object \8216") :<>: 'ShowType o) :<>: 'Text "\8217.")

class MethodInfo i o s where

Class for types containing the information about an overloaded method of type o -> s.

Methods

overloadedMethod :: o -> s