2015-11-09 08:01:19 -08:00
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<title>Sequence Class – Wren</title>
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2020-06-05 22:25:23 +00:00
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<h1><a href="../../">wren</a></h1>
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<h2>a classy little scripting language</h2>
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2020-06-05 22:25:23 +00:00
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2015-11-09 08:01:19 -08:00
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2020-06-05 22:25:23 +00:00
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2015-11-09 08:01:19 -08:00
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<h2>core classes</h2>
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<main>
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<h1>Sequence Class</h1>
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2020-06-05 22:25:23 +00:00
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<p>An abstract base class for any iterable object. Any class that implements the
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core <a href="../../control-flow.html#the-iterator-protocol">iterator protocol</a> can extend this to get a number of helpful methods.</p>
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2015-11-09 08:01:19 -08:00
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<h2>Methods <a href="#methods" name="methods" class="header-anchor">#</a></h2>
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<h3><strong>all</strong>(predicate) <a href="#all(predicate)" name="all(predicate)" class="header-anchor">#</a></h3>
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<p>Tests whether all the elements in the sequence pass the <code>predicate</code>.</p>
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<p>Iterates over the sequence, passing each element to the function <code>predicate</code>.
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If it returns something <a href="../control-flow.html#truth">false</a>, stops iterating
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and returns the value. Otherwise, returns <code>true</code>.</p>
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<pre class="snippet">
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System.print([1, 2, 3].all {|n| n > 2}) //> false
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System.print([1, 2, 3].all {|n| n < 4}) //> true
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</pre>
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<h3><strong>any</strong>(predicate) <a href="#any(predicate)" name="any(predicate)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Tests whether any element in the sequence passes the <code>predicate</code>.</p>
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<p>Iterates over the sequence, passing each element to the function <code>predicate</code>.
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If it returns something <a href="../../control-flow.html#truth">true</a>, stops iterating and
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returns that value. Otherwise, returns <code>false</code>.</p>
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<pre class="snippet">
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System.print([1, 2, 3].any {|n| n < 1}) //> false
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System.print([1, 2, 3].any {|n| n > 2}) //> true
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</pre>
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<h3><strong>contains</strong>(element) <a href="#contains(element)" name="contains(element)" class="header-anchor">#</a></h3>
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<p>Returns whether the sequence contains any element equal to the given element.</p>
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<h3><strong>count</strong> <a href="#count" name="count" class="header-anchor">#</a></h3>
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<p>The number of elements in the sequence.</p>
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<p>Unless a more efficient override is available, this will iterate over the
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sequence in order to determine how many elements it contains.</p>
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2015-11-09 08:01:19 -08:00
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<h3><strong>count</strong>(predicate) <a href="#count(predicate)" name="count(predicate)" class="header-anchor">#</a></h3>
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<p>Returns the number of elements in the sequence that pass the <code>predicate</code>.</p>
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<p>Iterates over the sequence, passing each element to the function <code>predicate</code>
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and counting the number of times the returned value evaluates to <code>true</code>.</p>
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<pre class="snippet">
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System.print([1, 2, 3].count {|n| n > 2}) //> 1
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System.print([1, 2, 3].count {|n| n < 4}) //> 3
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</pre>
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<h3><strong>each</strong>(function) <a href="#each(function)" name="each(function)" class="header-anchor">#</a></h3>
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<p>Iterates over the sequence, passing each element to the given <code>function</code>.</p>
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<pre class="snippet">
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["one", "two", "three"].each {|word| System.print(word) }
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</pre>
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<h3><strong>isEmpty</strong> <a href="#isempty" name="isempty" class="header-anchor">#</a></h3>
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<p>Returns whether the sequence contains any elements.</p>
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<p>This can be more efficient that <code>count == 0</code> because this does not iterate over
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the entire sequence.</p>
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<h3><strong>join</strong>(separator) <a href="#join(separator)" name="join(separator)" class="header-anchor">#</a></h3>
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<p>Converts every element in the sequence to a string and then joins the results
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together into a single string, each separated by <code>separator</code>.</p>
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<p>It is a runtime error if <code>separator</code> is not a string.</p>
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<h3><strong>join</strong>() <a href="#join()" name="join()" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Converts every element in the sequence to a string and then joins the results
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together into a single string.</p>
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2015-11-09 08:01:19 -08:00
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<h3><strong>map</strong>(transformation) <a href="#map(transformation)" name="map(transformation)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Creates a new sequence that applies the <code>transformation</code> to each element in the
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original sequence while it is iterated.</p>
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<pre class="snippet">
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var doubles = [1, 2, 3].map {|n| n * 2 }
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for (n in doubles) {
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System.print(n) //> 2
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//> 4
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//> 6
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}
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</pre>
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<p>The returned sequence is <em>lazy</em>. It only applies the mapping when you iterate
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over the sequence, and it does so by holding a reference to the original
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sequence.</p>
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<p>This means you can use <code>map(_)</code> for things like infinite sequences or sequences
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that have side effects when you iterate over them. But it also means that
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changes to the original sequence will be reflected in the mapped sequence.</p>
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<p>To force eager evaluation, just call <code>.toList</code> on the result.</p>
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<pre class="snippet">
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var numbers = [1, 2, 3]
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var doubles = numbers.map {|n| n * 2 }.toList
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numbers.add(4)
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System.print(doubles) //> [2, 4, 6]
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</pre>
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<h3><strong>reduce</strong>(function) <a href="#reduce(function)" name="reduce(function)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Reduces the sequence down to a single value. <code>function</code> is a function that
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takes two arguments, the accumulator and sequence item and returns the new
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accumulator value. The accumulator is initialized from the first item in the
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sequence. Then, the function is invoked on each remaining item in the sequence,
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iteratively updating the accumulator.</p>
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<p>It is a runtime error to call this on an empty sequence.</p>
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2015-11-09 08:01:19 -08:00
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<h3><strong>reduce</strong>(seed, function) <a href="#reduce(seed,-function)" name="reduce(seed,-function)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Similar to above, but uses <code>seed</code> for the initial value of the accumulator. If
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the sequence is empty, returns <code>seed</code>.</p>
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2017-10-19 07:05:45 -07:00
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<h3><strong>skip</strong>(count) <a href="#skip(count)" name="skip(count)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Creates a new sequence that skips the first <code>count</code> elements of the original
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sequence.</p>
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<p>The returned sequence is <em>lazy</em>. The first <code>count</code> elements are only skipped
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once you start to iterate the returned sequence. Changes to the original
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sequence will be reflected in the filtered sequence.</p>
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2017-10-19 07:05:45 -07:00
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<h3><strong>take</strong>(count) <a href="#take(count)" name="take(count)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Creates a new sequence that iterates only the first <code>count</code> elements of the
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original sequence.</p>
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<p>The returned sequence is <em>lazy</em>. Changes to the original sequence will be
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reflected in the filtered sequence.</p>
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2015-11-09 08:01:19 -08:00
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<h3><strong>toList</strong> <a href="#tolist" name="tolist" class="header-anchor">#</a></h3>
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<p>Creates a <a href="list.html">list</a> containing all the elements in the sequence.</p>
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<pre class="snippet">
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System.print((1..3).toList) //> [1, 2, 3]
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</pre>
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2015-11-09 08:01:19 -08:00
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2020-06-05 22:25:23 +00:00
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<p>If the sequence is already a list, this creates a copy of it.</p>
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2015-11-09 08:01:19 -08:00
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<h3><strong>where</strong>(predicate) <a href="#where(predicate)" name="where(predicate)" class="header-anchor">#</a></h3>
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2020-06-05 22:25:23 +00:00
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<p>Creates a new sequence containing only the elements from the original sequence
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that pass the <code>predicate</code>.</p>
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<p>During iteration, each element in the original sequence is passed to the
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function <code>predicate</code>. If it returns <code>false</code>, the element is skipped.</p>
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<pre class="snippet">
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var odds = (1..6).where {|n| n % 2 == 1 }
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for (n in odds) {
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System.print(n) //> 1
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//> 3
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//> 5
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}
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</pre>
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<p>The returned sequence is <em>lazy</em>. It only applies the filtering when you iterate
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over the sequence, and it does so by holding a reference to the original
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sequence.</p>
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<p>This means you can use <code>where(_)</code> for things like infinite sequences or
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sequences that have side effects when you iterate over them. But it also means
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that changes to the original sequence will be reflected in the filtered
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sequence.</p>
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<p>To force eager evaluation, just call <code>.toList</code> on the result.</p>
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<pre class="snippet">
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var numbers = [1, 2, 3, 4, 5, 6]
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var odds = numbers.where {|n| n % 2 == 1 }.toList
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numbers.add(7)
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System.print(odds) //> [1, 3, 5]
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</pre>
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2015-11-09 08:01:19 -08:00
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</main>
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</div>
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<footer>
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<div class="page">
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<div class="main-column">
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<p>Wren lives
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2019-02-06 02:52:27 +00:00
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<a href="https://github.com/wren-lang/wren">on GitHub</a>
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— Made with ❤ by
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<a href="http://journal.stuffwithstuff.com/">Bob Nystrom</a> and
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2020-06-12 17:15:45 +00:00
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<a href="https://github.com/wren-lang/wren/blob/main/AUTHORS">friends</a>.
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2015-11-09 08:01:19 -08:00
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</p>
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<div class="main-column">
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</footer>
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</body>
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