Ranges (pegjs/pegjs#30): Add documentation and examples

CHANGELOG.md

@@ -14,6 +14,8 @@ Released: TBD
   the documentation, from @hildjj
 - [#240](https://github.com/peggyjs/peggy/issues/240) Generate SourceNodes for bytecode
 - [#338](https://github.com/peggyjs/peggy/pull/338) BREAKING CHANGE. Update dependencies, causing minimum supported version of node.js to move to 14.  Generated grammar source should still work on older node versions and some older browsers, but testing is currently manual for those.
+- [#291](https://github.com/peggyjs/peggy/pull/291): Add support for repetition
+   operator `expression|min .. max, delimiter|`, from @Mingun
 
 ### Minor Changes
 

docs/documentation.html

@@ -780,6 +780,63 @@ <h3 id="grammar-syntax-and-semantics-parsing-expression-types">Parsing Expressio
 </div>
 </dd>
 
+<dt><code><em>expression</em> |count|
+      <br><em>expression</em> |min..max|
+      <br><em>expression</em> |count, delimiter|
+      <br><em>expression</em> |min..max, delimiter|</code></dt>
+
+<dd>
+  <p>Match exact <code>count</code> repetitions of <code>expression</code>.
+  If the match succeeds, return their match results in an array.</p>
+
+  <p><em>-or-</em></p>
+
+  <p>Match expression at least <code>min</code> but not more then <code>max</code> times.
+  If the match succeeds, return their match results in an array. Both <code>min</code>
+  and <code>max</code> may be omitted. If <code>min</code> is omitted, then it is assumed
+  to be <code>0</code>. If <code>max</code> is omitted, then it is assumed to be infinity.
+  Hence</p>
+
+  <ul>
+    <li><code>expression |..|</code> is an equivalent of <code>expression |0..|</code>
+    and <code>expression *</code></li>
+    <li><code>expression |1..|</code> is an equivalent of <code>expression +</code></li>
+  </ul>
+
+  <p>Optionally, <code>delimiter</code> expression can be specified. Delimiter must appear
+  between expressions exactly once and it is not included in the final array.</p>
+
+  <p><code>count</code>, <code>min</code> and <code>max</code> can be represented as:</p>
+
+  <ul>
+    <li>positive integer:
+      <pre><code class="language-peggy">start = "a"|2|;</code></pre>
+    </li>
+    <li>name of the preceding label:
+      <pre><code class="language-peggy">start = count:n1 "a"|count|;
+n1 = n:$[0-9] { return parseInt(n); };</code></pre>
+    </li>
+    <li>code block:
+      <pre><code class="language-peggy">start = "a"|{ return options.count; }|;</code></pre>
+    </li>
+    Any non-number values, returned by the code block, will be interpreted as <code>0</code>.
+  </ul>
+
+  <div class="example">
+    <div>
+      <div><em>Example:</em> <code>repetition = "a"|2..3, ","|</code></div>
+      <div><em>Matches:</em> <code>"a,a"</code>, <code>"a,a,a"</code></div>
+      <div><em>Does not match:</em> <code>"a"</code>, <code>"b,b"</code>,
+            <code>"a,a,a,"</code>, <code>"a,a,a,a"</code></div>
+    </div>
+    <div class="try">
+      <em>Try it:</em>
+      <input type="text" value="a,a" class="exampleInput" name="repetition">
+      <div class="result"></div>
+    </div>
+  </div>
+</dd>
+
 <dt><code><em>expression</em> ?</code></dt>
 
 <dd>
@@ -1124,6 +1181,21 @@ <h3 id="parsing-lists">Parsing Lists</h3>
 <p>One of the most frequent questions about Peggy grammars is how to parse a
 delimited list of items.  The cleanest current approach is:</p>
 
+<pre><code class="language-peggy">list = word|.., _ "," _|
+  word = $[a-z]i+
+  _ = [ \t]*</code></pre>
+
+<p>If you want to allow a trailing delimiter, append it to the end of the rule:</p>
+
+<pre><code class="language-peggy">list = word|.., delimiter| delimiter?
+  delimiter = _ "," _
+  word = $[a-z]i+
+  _ = [ \t]*</code></pre>
+
+<p>In the grammars created before the repetition operator was added to the peggy
+  (in 2.1.0) you could see that approach, which is equivalent of the new approach
+  with the repetition operator, but less efficient on long lists:</p>
+
 <pre><code class="language-peggy">list = head:word tail:(_ "," _ @word)* { return [head, ...tail]; }
 word = $[a-z]i+
 _ = [ \t]*</code></pre>