Function Composition in XQuery 3.1

compose.md

Function Composition in XQuery 3.1

Overview

This module provides a compose function.

Namespace

The module and default function namespaces are https://tinyurl.com/9apf36he.

Function: compose

Description

This function applies each function in the $functions sequence to the $items sequence. If $functions is empty, it returns $items. Otherwise, it recursively applies the first function in $functions to each item in $items, and then calls itself with the result and the remaining functions.

Parameters

• $items: The items to be processed. It is of type item()*.
• $functions: The functions to be applied to the items. It is of type function(item()*)*.

Returns

The result of applying each function to the items. The return type is item()*.

Usage

declare function compose(
    $items as item()*,
    $functions as function(item()*) as item()**
) as item()* {
    if (fn:empty($functions)) then $items
    else compose(fn:for-each($items, fn:head($functions)), fn:tail($functions))
};

References

: https://en.wikipedia.org/wiki/Function_composition_(computer_science)

compose.xqy

(:~
 : @version 1.0
 : @see https://tinyurl.com/9apf36he
 : @module.description This module provides a compose function.
 :)
xquery version "3.1";

module namespace compose = "https://tinyurl.com/9apf36he";

declare default function namespace "https://tinyurl.com/9apf36he";

(:~
 : @function.description This function applies each function in the $functions 
 : sequence to the $items sequence. If $functions is empty, it returns $items. 
 : Otherwise, it recursively applies the first function in $functions to each 
 : item in $items, and then calls itself with the result and the remaining 
 : functions.
 : @param $items The items to be processed.
 : @param $functions The functions to be applied to the items.
 : @return The result of applying each function to the items.
 :)
declare function compose(
    $items as item()*,
    $functions as function(item()*) as item()**
) as item()* {
    if (fn:empty($functions)) then $items
    else compose(fn:for-each($items, fn:head($functions)), fn:tail($functions))
};