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1685 Pipeline Operator #1686

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1685 Pipeline Operator #1686

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895ffaf
Pipeline Operator. Closes #1685
ChristianGruen Jan 9, 2025
2fe5867
PR/issue number added to change section
ChristianGruen Jan 9, 2025
54f76d9
Minor edit
ChristianGruen Jan 9, 2025
7ff57d5
Grammar rules updated. #1685
ChristianGruen Jan 12, 2025
3b36b6d
Minor fix. #1685
ChristianGruen Jan 12, 2025
e2b7d56
Examples revised
ChristianGruen Jan 16, 2025
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5 changes: 5 additions & 0 deletions specifications/grammar-40/xpath-grammar.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -1553,6 +1553,11 @@ ErrorVal ::= "$" VarName
</g:sequence>
</g:postfix>
</g:level>
<g:level>
<g:binary name="PipelineExpr" condition="&gt; 1" if="xpath40 xquery40">
<g:string>-></g:string>
</g:binary>
</g:level>
<g:level>
<g:postfix name="ArrowExpr" prefix-seq-type="*" condition="&gt; 1" if="xpath40 xquery40">
<g:sequence>
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98 changes: 98 additions & 0 deletions specifications/xquery-40/src/expressions.xml
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Expand Up @@ -22054,6 +22054,104 @@ raised <errorref
</div3>
</div2>

<div2 id="id-pipeline-operator">
<head>Pipeline operator</head>

<changes>
<change issue="1685" PR="1686" date="2025-01-09">
With the pipeline operator <code>-></code>, the result of an expression
can be bound to the context value before evaluating another expression.
</change>
</changes>

<scrap>
<head/>
<prodrecap id="PipelineExpr" ref="PipelineExpr"/>
</scrap>

<p diff="add" at="A"><termdef term="pipeline operator" id="dt-pipeline-operator">
The <term>pipeline operator</term> <code>-></code> evaluates an expression and
binds the result to the context value before evaluating another expression.</termdef></p>

<p>Each operation <code><var>E1</var> -> <var>E2</var></code> is evaluated as follows:
Expression <var>E1</var> is evaluated to a sequence <code>S</code>.
<var>S</var> then serves in turn to provide an inner <termref def="dt-fixed-focus"/>
(with the context value set to <var>S</var>) for an evaluation of <var>E2</var> in the
<termref def="dt-dynamic-context">dynamic context</termref>.
Unlike the <specref ref="id-map-operator"/>, the result of <var>E1</var> is bound
just once and as a whole to the context value.
</p>

<p>The following examples illustrate the use of pipeline operators:</p>
<example>
<ulist>
<item>
<p>Tokenizes a string, counts the tokens, creates a concatenated string and returns
<code>count=3</code>:</p>
<eg role="parse-test">'a b c' -> tokenize(.) -> count(.) -> concat('count=', .)
</eg>
<p>An equivalent expression is:
<eg role="parse-test">
let $string := 'a b c'
let $tokens := tokenize($string)
let $count := count($tokens)
return concat('count=', $count)
</eg>
</p>
</item>
<item>
<p>Calculates the sum of powers of <code>2</code> and returns
<code>2046</code>.</p>
<eg role="parse-test">(1 to 10) ! math:pow(2, .) -> sum(.)</eg>
<p>An equivalent expression is:
<eg role="parse-test">
let $powers := (
for $exp in 1 to 10
return math:pow(2, $exp)
)
return sum($powers)
</eg>
</p>
</item>
<item>
<p>Doubles the values of a sequence, compares the values pairwise with another
sequence, checks if some comparisons were successful, and returns
<code>true</code>.</p>
<eg role="parse-test">
(1 to 4)
-> for-each(., op('+'))
-> for-each-pair(4 to 7, ., op('>'))
-> some(.)
</eg>
<p>An equivalent expression is:
<eg role="parse-test">
let $data := 1 to 4
let $data := for-each($data, op('+'))
let $data := for-each-pair(4 to 7, $data, op('>'))
return some($data)
</eg>
</p>
</item>
<item>
<p>Reduces a long sequence to at most 9 elements, with dots appended,
and returns a single string.</p>
<eg role="parse-test">
$dictionary/word
-> (if(count(.) &lt; 10) then . else (.[1 to 9], '…'))
-> string-join(., '; ')
</eg>
<p>An equivalent expression is:
<eg role="parse-test">
let $words := $dictionary/word
let $chopped := (if(count($words) &lt; 10) then $words else ($words[1 to 9], '…'))
return string-join($chopped, '; ')
</eg>
</p>
</item>
</ulist>
</example>
</div2>

<div2 id="id-map-operator">
<head>Simple map operator (<code>!</code>)</head>

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