fn:while. qt4cg#80

ChristianGruen · Oct 13, 2022 · 04ea1b5 · 04ea1b5
1 parent 318c353
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diff --git a/specifications/xpath-functions-40/src/function-catalog.xml b/specifications/xpath-functions-40/src/function-catalog.xml
@@ -16579,6 +16579,86 @@ declare function fn:fold-right(
          </fos:example>
       </fos:examples>
    </fos:function>
+   <fos:function name="while" prefix="fn">
+      <fos:signatures>
+         <fos:proto name="while" return-type="item()*">
+            <fos:arg name="input" type="item()*"/>
+            <fos:arg name="predicate" type="function(item()*) as xs:boolean"/>
+            <fos:arg name="action" type="function(item()*) as item()*"/>
+         </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>Applies the predicate function to the supplied input. In case of success, the input
+           is returned. Otherwise, the input is passed on to the action function, and the result is 
+           applied to the predicate function and returned or taken as new input.</p>
+      </fos:summary>
+      <fos:rules>
+         <p>The effect of the function is equivalent to the following implementation in XQuery:</p>
+         <eg><![CDATA[
+declare function fn:while(
+  $input     as item()*,
+  $predicate as function(item()*) as xs:boolean,
+  $action    as function(item()*) as item()*
+) as item()* {
+  if ($predicate($input)) then (
+    fn:while($action($input), $predicate, $action)
+  ) else (
+    $input
+  )
+};]]></eg>
+      </fos:rules>
+      <fos:errors>
+         <p>As a consequence of the function signature and the function calling rules, a type error
+            occurs if the supplied predicate function cannot be applied to a single argument, or if
+            if returns anything other than a single <code>xs:boolean</code> item; there is no
+            conversion to an effective boolean value. Alternatively, an error occurs if the supplied
+            action function cannot be applied to a single argument.</p>
+      </fos:errors>
+      <fos:examples>
+         <fos:example>
+            <fos:test>
+               <fos:expression><![CDATA[fn:while(2, -> { . < 100 }, -> { . * . })]]></fos:expression>
+               <fos:result>256</fos:result>
+            </fos:test>
+         </fos:example>
+         <fos:example>
+            <fos:test>
+               <fos:expression><![CDATA[fn:while(
+  1 to 9,
+  function($seq) { head($seq) < 5 },
+  function($seq) { tail($seq) }
+)]]></fos:expression>
+               <fos:result>(5, 6, 7, 8, 9)</fos:result>
+            </fos:test>
+         </fos:example>
+         <fos:example>
+            <fos:test>
+               <fos:expression><![CDATA[let $input := 3936256
+return fn:while(
+  $input,
+  function($result) { abs($result * $result - $input) >= 0.0000000001 },
+  function($guess) { ($guess + $input div $guess) div 2 }
+)]]></fos:expression>
+               <fos:result>1984</fos:result>
+               <fos:postamble>This computes the square root of a number.</fos:postamble>
+            </fos:test>
+         </fos:example>
+         <fos:example>
+            <fos:test>
+               <fos:expression><![CDATA[let $input := (0 to 4, 6 to 10)
+return fn:while(0, function($n) { $n = $input }, function($n) { $n + 1 })]]></fos:expression>
+               <fos:result>5</fos:result>
+               <fos:postamble>This returns the first positive number missing in a sequence.</fos:postamble>
+            </fos:test>
+         </fos:example>
+      </fos:examples>
+   </fos:function>
    <fos:function name="for-each-pair" prefix="fn">
       <fos:signatures>
          <fos:proto name="for-each-pair" return-type="item()*">

diff --git a/specifications/xpath-functions-40/src/xpath-functions.xml b/specifications/xpath-functions-40/src/xpath-functions.xml
@@ -5888,6 +5888,9 @@ correctly in all browsers, depending on the system configuration.</emph></p>-->
             <div3 id="func-fold-right">
                <head><?function fn:fold-right?></head>
             </div3>
+            <div3 id="func-while">
+               <head><?function fn:while?></head>
+            </div3>
             <div3 id="func-for-each-pair">
                <head><?function fn:for-each-pair?></head>
             </div3>