Mu.Schema.Annotations

Libraries can define custom annotations to indicate additional information not found in the Schema itself. For example, Protocol Buffers requires a numerical identifier for each field in a record.

Annotate a schema

data Annotation domain typeName fieldName where

Annotations proper.

Constructors

AnnSchema :: domain -> Annotation domain typeName fieldName

Annotation over the whole schema.

AnnType :: typeName -> domain -> Annotation domain typeName fieldName

Annotation over a type in the schema.

AnnField :: typeName -> fieldName -> domain -> Annotation domain typeName fieldName

Annotation over a field in a record or a choice in an enumeration.

type family AnnotatedSchema domain (sch :: Schema typeName fieldName) :: [Annotation domain typeName fieldName]

This type family links each schema to its corresponding annotations from one domain.

type AnnotationDomain = Type

Each annotation belongs to a domain.

Find annotations for an element

type family GetSchemaAnnotation (anns :: [Annotation domain t f]) :: domain where ...

Find the annotation over the schema in the given set. If the annotation cannot be found, raise a TypeError.

Equations

GetSchemaAnnotation '[] = TypeError (Text "cannot find schema annotation")

GetSchemaAnnotation (AnnSchema d ': rs) = d

GetSchemaAnnotation (r ': rs) = GetSchemaAnnotation rs

type family GetTypeAnnotation (anns :: [Annotation domain t f]) (ty :: t) :: domain where ...

Find the annotation over the given type in the given set. If the annotation cannot be found, raise a TypeError.

Equations

GetTypeAnnotation '[] ty = TypeError (Text "cannot find annotation for " :<>: ShowType ty)

GetTypeAnnotation (AnnType ty d ': rs) ty = d

GetTypeAnnotation (r ': rs) ty = GetTypeAnnotation rs ty

type family GetFieldAnnotation (anns :: [Annotation domain t f]) (ty :: t) (fl :: f) :: domain where ...

Find the annotation over the given field or choice in the given type. If the annotation cannot be found, raise a TypeError.

Equations

GetFieldAnnotation '[] ty fl = TypeError (((Text "cannot find annotation for " :<>: ShowType ty) :<>: Text "/") :<>: ShowType fl)

GetFieldAnnotation (AnnField ty fl d ': rs) ty fl = d

GetFieldAnnotation (r ': rs) ty fl = GetFieldAnnotation rs ty fl