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 <div class="section s2">
  <h1 class="title h2"><span><span class="section-number">6.6</span> FParsec.Reply</span></h1>
  <div class="intro i2">
   <div class="para _1">
    <p>
     Represents the return value of a <code class="fsharp"><a href="primitives.html#members.Parser"><span class="ci">Parser</span></a></code>
     function.
    </p>
   </div>
  </div>
  <div id="interface" class="section s3">
   <h2 class="title h3"><span><span class="section-number">6.6.1</span> Interface</span></h2>
   <div class="intro i3">
    <div class="para _1 lcinp">
     <div class="interface-code">
<pre class="code fsharp"><span class="clc"><span class="cld">//</span> FParsecCS.dll</span>

<span class="ck">namespace</span> <span class="ci">FParsec</span>

<span class="ck">type</span> <span class="a" id="interface.ReplyStatus"><span class="ci">ReplyStatus</span></span> <span class="cp">=</span> <span class="a" id="interface.ReplyStatus..Ok"><span class="ci">Ok</span></span>         <span class="co">=</span>  <span class="cn">1</span>
                 <span class="cp">|</span> <span class="a" id="interface.ReplyStatus..Error"><span class="ci">Error</span></span>      <span class="co">=</span>  <span class="cn">0</span>
                 <span class="cp">|</span> <span class="a" id="interface.ReplyStatus..FatalError"><span class="ci">FatalError</span></span> <span class="co">=</span> <span class="co">-</span><span class="cn">1</span>


<span class="ck">type</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span> <span class="cp">=</span> <span class="ck">struct</span>
  <a id="interface.new-1:B:" href="#members.new-1"><span class="interface-member-marker"><span class="ck">new</span></span></a><span class="cp">:</span> <span class="ctv">'TResult</span> <span class="cr">-&gt;</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span>
  <a id="interface.new-2:B:" href="#members.new-2"><span class="interface-member-marker"><span class="ck">new</span></span></a><span class="cp">:</span> <a href="#interface.ReplyStatus"><span class="ci">ReplyStatus</span></a> <span class="cp">*</span> <a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a> <span class="cr">-&gt;</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span>
  <a id="interface.new-3:B:" href="#members.new-3"><span class="interface-member-marker"><span class="ck">new</span></span></a><span class="cp">:</span> <a href="#interface.ReplyStatus"><span class="ci">ReplyStatus</span></a> <span class="cp">*</span> <span class="ctv">'TResult</span> <span class="cp">*</span> <a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a> <span class="cr">-&gt;</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span>

  <span class="ck">val</span> <span class="ck">mutable</span> <a id="interface.Status:B:" href="#members.Status"><span class="interface-member-marker"><span class="ci">Status</span></span></a><span class="cp">:</span> <a href="#interface.ReplyStatus"><span class="ci">ReplyStatus</span></a>
  <span class="clc"><span class="cld">//</span>/ If Status &lt;&gt; Ok then the Result value is undefined and may be null.</span>
  <span class="ck">val</span> <span class="ck">mutable</span> <a id="interface.Result:B:" href="#members.Result"><span class="interface-member-marker"><span class="ci">Result</span></span></a><span class="cp">:</span> <span class="ctv">'TResult</span>
  <span class="ck">val</span> <span class="ck">mutable</span> <a id="interface.Error:B:" href="#members.Error"><span class="interface-member-marker"><span class="ci">Error</span></span></a><span class="cp">:</span> <a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a>

  <span class="ck">override</span> <span class="ci">Equals</span><span class="cp">:</span> <span class="ci">obj</span> <span class="cr">-&gt;</span> <span class="ci">bool</span>
  <span class="ck">override</span> <span class="ci">GetHashCode</span><span class="cp">:</span> <span class="ci">unit</span> <span class="cr">-&gt;</span> <span class="ci">int</span>
  <span class="ck">interface</span> <a href="http://msdn.microsoft.com/en-us/library/ms131187.aspx"><span class="ci">System</span><span class="cm">.</span><span class="ci">IEquatable</span></a><span class="cp">&lt;</span><span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span><span class="cp">&gt;</span>
<span class="ck">end</span>
</pre>
     </div>
    </div>
   </div>
  </div>
  <div id="remarks" class="section s3">
   <h2 class="title h3"><span><span class="section-number">6.6.2</span> Remarks</span></h2>
   <div class="intro i3">
    <div class="para _1">
     <p>
      The <code class="fsharp"><span class="ci">Reply</span></code> type is the return type of <code class="fsharp"><a
      href="primitives.html#members.Parser"><span class="ci">Parser</span></a></code> functions. Similar to a tuple, a <code class="fsharp"><span
      class="ci">Reply</span></code> value can be viewed as a simple aggregate of its three fields <code class="fsharp"><a
      href="#members.Status"><span class="ci">Status</span></a></code>, <code class="fsharp"><a href="#members.Result"><span
      class="ci">Result</span></a></code> and <code class="fsharp"><a href="error.html"><span class="ci">Error</span></a></code>.
     </p>
    </div>
    <div class="para _2">
     <p>
      The value of the <code class="fsharp"><a href="#members.Status"><span class="ci">Status</span></a></code> field indicates whether the parser
      returning the reply succeeded (<code class="fsharp"><a href="#interface.ReplyStatus..Ok"><span class="ci">ReplyStatus</span><span
      class="cm">.</span><span class="ci">Ok</span></a></code>) or failed (<code class="fsharp"><a href="#interface.ReplyStatus..Error"><span
      class="ci">ReplyStatus</span><span class="cm">.</span><span class="ci">Error</span></a></code> or <code class="fsharp"><a
      href="#interface.ReplyStatus..FatalError"><span class="ci">ReplyStatus</span><span class="cm">.</span><span
      class="ci">FatalError</span></a></code>). If the value of the <code class="fsharp"><a href="#members.Status"><span
      class="ci">Status</span></a></code> field is <code class="fsharp"><a href="primitives.html#members.Ok"><span class="ci">Ok</span></a></code>,
      the <code class="fsharp"><a href="#members.Result"><span class="ci">Result</span></a></code> field contains a parser result value; otherwise,
      its value is undefined.
     </p>
    </div>
    <div class="para _3">
     <p>
      The <code class="fsharp"><span class="ci">Equals</span></code> override ignores the <code class="fsharp"><a href="#members.Result"><span
      class="ci">Result</span></a></code> value when it compares two <code class="fsharp"><span class="ci">Reply</span></code> values with <code
      class="fsharp"><a href="#members.Status"><span class="ci">Status</span></a> <span class="co">&lt;&gt;</span> <a
      href="primitives.html#members.Ok"><span class="ci">Ok</span></a></code>.
     </p>
    </div>
    <div class="para _4 lcinp">
     <div class="admonition">
      <div class="admonition-title">Note</div>
      <div class="admonition-body">
       <div class="para _1">
        <p>
         The <code class="fsharp"><span class="ci">Reply</span></code> fields are mutable because that allows us to implement library primitives with
         more compact code, for which the .NET JIT produces faster machine code.
        </p>
       </div>
       <div class="para _2">
        <p>
         Of course, if you object to mutable structs <a href="http://stackoverflow.com/questions/441309/why-are-mutable-structs-evil">on religious
         grounds</a> or if you’re not familiar with the somewhat subtle behaviour of mutable structs in certain sitations, you can always treat the
         <code class="fsharp"><span class="ci">Reply</span></code> type as if it was immutable.
        </p>
       </div>
      </div>
     </div>
    </div>
   </div>
  </div>
  <div id="members" class="section s3">
   <h2 class="title h3"><span><span class="section-number">6.6.3</span> Members</span></h2>
   <div class="intro i3">
    <div class="para _1 lcinp">
     <div class="interface-members">
      <div class="interface-member _1" id="members.new-1">
       <div class="interface-member-code">
        <a class="interface-member-backlink" href="#interface.new-1:B:"></a>
<pre class="code fsharp"><span class="interface-member-marker"><span class="ck">new</span></span><span class="cp">:</span> <span class="ctv">'TResult</span> <span class="cr">-&gt;</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span>
</pre>
       </div>
       <div class="interface-member-description">
        <div class="para _1">
         <p>
          Constructs a <code class="fsharp"><span class="ci">Reply</span></code> instance with the <code class="fsharp"><a
          href="#members.Status"><span class="ci">Status</span></a></code> field set to <code class="fsharp"><a
          href="primitives.html#members.Ok"><span class="ci">Ok</span></a></code>, the <code class="fsharp"><a href="#members.Result"><span
          class="ci">Result</span></a></code> field set to the argument value and the <code class="fsharp"><a href="#members.Error"><span
          class="ci">Error</span></a></code> field set to <code class="fsharp"><span class="cnu">null</span></code>.
         </p>
        </div>
       </div>
      </div>
      <div class="interface-member _2" id="members.new-2">
       <div class="interface-member-code">
        <a class="interface-member-backlink" href="#interface.new-2:B:"></a>
<pre class="code fsharp"><span class="interface-member-marker"><span class="ck">new</span></span><span class="cp">:</span> <a href="#interface.ReplyStatus"><span class="ci">ReplyStatus</span></a> <span class="cp">*</span> <a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a> <span class="cr">-&gt;</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span>
</pre>
       </div>
       <div class="interface-member-description">
        <div class="para _1">
         <p>
          Constructs a <code class="fsharp"><span class="ci">Reply</span></code> instance with the <code class="fsharp"><a
          href="#members.Status"><span class="ci">Status</span></a></code> and <code class="fsharp"><a href="#members.Error"><span
          class="ci">Error</span></a></code> fields set to the respective argument values and the <code class="fsharp"><a href="#members.Result"><span
          class="ci">Result</span></a></code> field initialized to <code class="fsharp"><span class="ci">Unchecked</span><span
          class="cm">.</span><span class="ci">defaultof</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span
          class="cp">&gt;</span></code>.
         </p>
        </div>
        <div class="para _2">
         <p>
          This constructor is usually used for constructing an error reply, like in <code class="fsharp"><span class="ci">Reply</span><span
          class="cp">(</span><a href="primitives.html#members.Error"><span class="ci">Error</span></a><span class="cp">,</span> <a
          href="error.html#members.expected"><span class="ci">expected</span></a> <span class="cs"><span class="cld">"</span>something<span
          class="crd">"</span></span><span class="cp">)</span></code>.
         </p>
        </div>
       </div>
      </div>
      <div class="interface-member _3" id="members.new-3">
       <div class="interface-member-code">
        <a class="interface-member-backlink" href="#interface.new-3:B:"></a>
<pre class="code fsharp"><span class="interface-member-marker"><span class="ck">new</span></span><span class="cp">:</span> <a href="#interface.ReplyStatus"><span class="ci">ReplyStatus</span></a> <span class="cp">*</span> <span class="ctv">'TResult</span> <span class="cp">*</span> <a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a> <span class="cr">-&gt;</span> <span class="ci">Reply</span><span class="cp">&lt;</span><span class="ctv">'TResult</span><span class="cp">&gt;</span>
</pre>
       </div>
       <div class="interface-member-description">
        <div class="para _1">
         <p>
          Constructs a <code class="fsharp"><span class="ci">Reply</span></code> instance with the <code class="fsharp"><a
          href="#members.Status"><span class="ci">Status</span></a></code>, <code class="fsharp"><a href="#members.Result"><span
          class="ci">Result</span></a></code> and <code class="fsharp"><a href="#members.Error"><span class="ci">Error</span></a></code> fields set to
          the respective argument values.
         </p>
        </div>
       </div>
      </div>
      <div class="interface-member _4" id="members.Status">
       <div class="interface-member-code">
        <a class="interface-member-backlink" href="#interface.Status:B:"></a>
<pre class="code fsharp"><span class="ck">val</span> <span class="ck">mutable</span> <span class="interface-member-marker"><span class="ci">Status</span></span><span class="cp">:</span> <a href="#interface.ReplyStatus"><span class="ci">ReplyStatus</span></a>
</pre>
       </div>
       <div class="interface-member-description">
        <div class="para _1">
         <p>
          The <code class="fsharp"><span class="ci">Status</span></code> field contains a <code class="fsharp"><a href="#interface.ReplyStatus"><span
          class="ci">ReplyStatus</span></a></code> enum value indicating whether a parser succeeded (<code class="fsharp"><a
          href="primitives.html#members.Ok"><span class="ci">Ok</span></a></code>) or failed (<code class="fsharp"><a
          href="primitives.html#members.Error"><span class="ci">Error</span></a></code> or <code class="fsharp"><a
          href="primitives.html#members.FatalError"><span class="ci">FatalError</span></a></code>). By returning a <code class="fsharp"><a
          href="primitives.html#members.FatalError"><span class="ci">FatalError</span></a></code> instead of an <code class="fsharp"><a
          href="primitives.html#members.Error"><span class="ci">Error</span></a></code> a parser can signal that no error recovery should be tried
          (except through backtracking mechanisms).
         </p>
        </div>
       </div>
      </div>
      <div class="interface-member _5" id="members.Result">
       <div class="interface-member-code">
        <a class="interface-member-backlink" href="#interface.Result:B:"></a>
<pre class="code fsharp"><span class="ck">val</span> <span class="ck">mutable</span> <span class="interface-member-marker"><span class="ci">Result</span></span><span class="cp">:</span> <span class="ctv">'TResult</span>
</pre>
       </div>
       <div class="interface-member-description">
        <div class="para _1">
         <p>
          If the value of the <code class="fsharp"><a href="#members.Status"><span class="ci">Status</span></a></code> field is <code
          class="fsharp"><a href="primitives.html#members.Ok"><span class="ci">Ok</span></a></code>, the <code class="fsharp"><span
          class="ci">Result</span></code> field contains a parser result value; otherwise, its value is undefined and may be equal to <code
          class="fsharp"><span class="ci">Unchecked</span><span class="cm">.</span><span class="ci">defaultof</span><span class="cp">&lt;</span><span
          class="ctv">'TResult</span><span class="cp">&gt;</span></code>. (The result value in a <code class="fsharp"><span
          class="ci">Reply</span></code> returned by an unsuccessful parser is generally an implementation detail of the parser that you should not
          depend on.)
         </p>
        </div>
       </div>
      </div>
      <div class="interface-member _6" id="members.Error">
       <div class="interface-member-code">
        <a class="interface-member-backlink" href="#interface.Error:B:"></a>
<pre class="code fsharp"><span class="ck">val</span> <span class="ck">mutable</span> <span class="interface-member-marker"><span class="ci">Error</span></span><span class="cp">:</span> <a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a>
</pre>
       </div>
       <div class="interface-member-description">
        <div class="para _1">
         <p>
          The <code class="fsharp"><span class="ci">Error</span></code> field holds a list of error messages in the form of an <code class="fsharp"><a
          href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a></code> value. An empty <code class="fsharp"><a
          href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a></code> is represented as a <code class="fsharp"><span
          class="cnu">null</span></code> value.
         </p>
        </div>
        <div class="para _2">
         <p>
          The error messages returned by a parser in a <code class="fsharp"><span class="ci">Reply</span></code> value implicitly refer to the state
          of the <code class="fsharp"><a href="charstream.html#CharStream"><span class="ci">CharStream</span></a></code> as it is when the parser
          returns. Since the <code class="fsharp"><a href="errormessage.html#members.ErrorMessage"><span class="ci">ErrorMessage</span></a></code>
          values stored in the <code class="fsharp"><a href="errormessagelist.html"><span class="ci">ErrorMessageList</span></a></code> do not
          themselves contain an error position, they can only be interpreted together with the position of the <code class="fsharp"><a
          href="charstream.html#CharStream"><span class="ci">CharStream</span></a></code> as it is when the parser returns.
         </p>
        </div>
       </div>
      </div>
     </div>
    </div>
   </div>
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