Add specification for fn:op() (issue qt4cg#83)

michaelhkay · Oct 18, 2022 · b7aec53 · b7aec53
1 parent c24cec3
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diff --git a/specifications/xpath-functions-40/src/function-catalog.xml b/specifications/xpath-functions-40/src/function-catalog.xml
@@ -16853,6 +16853,65 @@ return fn:sort($in, $SWEDISH)
          </fos:example>
       </fos:examples>
    </fos:function>
+
+   <fos:function name="op" prefix="fn">
+      <fos:signatures>
+         <fos:proto name="op" return-type="function(item()*, item()*) as item()*">
+            <fos:arg name="operator" type="xs:string"/>
+         </fos:proto>
+      </fos:signatures>
+      <fos:properties>
+         <fos:property>deterministic</fos:property>
+         <fos:property>context-independent</fos:property>
+         <fos:property>focus-independent</fos:property>
+         <fos:property>higher-order</fos:property>
+      </fos:properties>
+      <fos:summary>
+         <p>Returns a function whose effect is to apply a supplied binary operator to two arguments.</p>
+      </fos:summary>
+      <fos:rules>
+         <p>The supplied operator must be one of the following:</p>
+         <p><code><![CDATA[",", "and", "or", 
+            "+", "-", "", "div", "idiv", "mod",
+            "=", "<", "<=", ">", ">=", "!=",
+            "eq", "lt", "le", "gt", "ge", "ne",
+            "<<", ">>", "is", "||", "|",
+            "union", "except", "intersect", "to",
+            "otherwise"]]></code></p>
+         <p>The result of calling <code>fn:op("⊙")</code>, where <code>⊙</code> is one of the above operators, is
+         the function represented by the XPath expression:</p>
+         <p><code>function($x, $y) { $x ⊙ $y }</code></p>
+         <p>For example, <code>op("+")</code> returns <code>function($x, $y) { $x + $y }</code>.</p>
+      </fos:rules>
+      <fos:errors>
+         <p>A dynamic error is raised if the supplied argument is not one of the supported operators ([TODO: error code]).
+         </p>
+      </fos:errors>
+      <fos:notes>
+         <p>The function is useful in contexts where an arity-2 callback function needs to be supplied, and
+            a standard operator meets the requirement.</p>
+         <p>For example, the XSLT <code>xsl:map</code> instruction
+            has an <code>on-duplicates</code> attribute that expects such a function. Specifying
+         <code>on-duplicates="op(',')"</code> is equivalent to specifying 
+         <code>on-duplicates="function($x, $y) { $x, $y }</code></p>
+         <p>The function is also useful in cases where the choice of operator to apply is
+         made dynamically.</p>
+      </fos:notes>
+      <fos:examples>
+         <fos:example>
+            <fos:test>
+               <fos:expression>fn:for-each-pair(21 to 25, 1 to 5, fn:op("+"))</fos:expression>
+               <fos:result>22, 24, 26, 28, 30</fos:result>
+            </fos:test>
+         </fos:example>
+         <fos:example>
+            <fos:test>
+               <fos:expression>fn:for-each-pair(21 to 25, 1 to 5, fn:op("-"))</fos:expression>
+               <fos:result>20, 20, 20, 20, 20</fos:result>
+            </fos:test>
+         </fos:example>
+      </fos:examples>
+   </fos:function>
 
    <fos:function name="same-key" prefix="op">
       <fos:signatures>

diff --git a/specifications/xpath-functions-40/src/xpath-functions.xml b/specifications/xpath-functions-40/src/xpath-functions.xml
@@ -5928,14 +5928,18 @@ correctly in all browsers, depending on the system configuration.</emph></p>-->
          </div2>
          <div2 id="dynamic-loading">
             <head>Dynamic Loading</head>
-            <p>The following functions allow dynamic loading and execution of XQuery queries and XSLT stylesheets.</p>
+            <p>The following functions allow dynamic loading and execution of XQuery queries and XSLT stylesheets,
+               or XPath operators.</p>
             <?local-function-index?>
             <div3 id="func-load-xquery-module">
                <head><?function fn:load-xquery-module?></head>
             </div3>
             <div3 id="func-transform">
                <head><?function fn:transform?></head>
             </div3>
+            <div3 id="func-op">
+               <head><?function fn:op?></head>
+            </div3>
          </div2>
       </div1>