Proposal for Annotation Sequence Types (XQuery only)

annotation-sequence-types.md

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+# Annotation Sequence Types (XQuery only)
+
+**Author**: Reece H. Dunn. 67 Bricks.
+
+This proposal adds annotation signatures to the XQuery type system.
+
+
+## Description
+
+It is not currently possible to access annotation information for a function in XQuery. Adding support for that to the XQuery Functions and Operators would need a way of specifying the annotations in return and parameter types, and thus be describable in the type system.
+
+The new annotation types may also be used when specifying the type of the proposed annotation declarations.
+
+The annotation type is modelled on the `FunctionTest` syntax. Annotation types cannot have a return type. For example:
+
+1. `annotation(*)`
+1. `%compatibility-annotation annotation()`
+1. `annotation(xs:string)`
+1. `annotation(variadic array(xs:string))` -- using the syntax from the variadic function parameter proposal.
+
+The type matching rules should follow the same logic as matching functions, excluding the return type.
+
+The type of an `Annotation` will be as follows:
+
+1. The number of parameter types will match the number of arguments the annotation is called with.
+1. If a parameter is a `StringLiteral`, it will have the type `xs:string`.
+1. If a parameter is a `DoubleLiteral`, it will have the type `xs:double`.
+1. If a parameter is a `DecimalLiteral`, it will have the type `xs:decimal`.
+1. If a parameter is a `IntegerLiteral`, it will have the type `xs:integer`.
+
+### Extending the Annotation Declaration Proposal
+
+The type of an annotation declaration will match the type signature for that declaration.
+
+The type of a named annotation reference will be the type signature of the matching annotation declaration.
+
+If a named annotation reference refers to a variadic function parameter (if that proposal is accepted), the reference will refer to the expanded non-variadic signature, and the parameters after the last non-variadic parameter will have the type specified in the `ArrayTest` or `item()` if a type is not specified.
+
+
+## Use Cases
+
+Provide access to annotations in the XQuery code.
+
+Make the XQuery type system more complete by making annotations part of the data model.
+
+
+## Examples
+
+    let $post as annotation()? := annotation-for-function($f, %rest:POST#1)
+    return exists($post)
+
+
+## Grammar
+
+TBD.