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href="Tk.html"> <link title="Unix" rel="Chapter" href="Unix.html"> <link title="UnixLabels" rel="Chapter" href="UnixLabels.html"> <link title="Weak" rel="Chapter" href="Weak.html"><title>Lazy</title> </head> <body> <div class="navbar"><a class="pre" href="Int64.html" title="Int64">Previous</a> <a class="up" href="index.html" title="Index">Up</a> <a class="post" href="Lexing.html" title="Lexing">Next</a> </div> <h1>Module <a href="type_Lazy.html">Lazy</a></h1> <pre><span class="keyword">module</span> Lazy: <code class="code"><span class="keyword">sig</span></code> <a href="Lazy.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info module top"> Deferred computations.<br> </div> <hr width="100%"> <pre><span id="TYPEt"><span class="keyword">type</span> <code class="type">'a</code> t</span> = <code class="type">'a lazy_t</code> </pre> <div class="info "> A value of type <code class="code"><span class="keywordsign">'</span>a <span class="constructor">Lazy</span>.t</code> is a deferred computation, called a suspension, that has a result of type <code class="code"><span class="keywordsign">'</span>a</code>. The special expression syntax <code class="code"><span class="keyword">lazy</span> (expr)</code> makes a suspension of the computation of <code class="code">expr</code>, without computing <code class="code">expr</code> itself yet. "Forcing" the suspension will then compute <code class="code">expr</code> and return its result. <p> Note: <code class="code">lazy_t</code> is the built-in type constructor used by the compiler for the <code class="code"><span class="keyword">lazy</span></code> keyword. You should not use it directly. Always use <code class="code"><span class="constructor">Lazy</span>.t</code> instead. <p> Note: <code class="code"><span class="constructor">Lazy</span>.force</code> is not thread-safe. If you use this module in a multi-threaded program, you will need to add some locks. <p> Note: if the program is compiled with the <code class="code">-rectypes</code> option, ill-founded recursive definitions of the form <code class="code"><span class="keyword">let</span> <span class="keyword">rec</span> x = <span class="keyword">lazy</span> x</code> or <code class="code"><span class="keyword">let</span> <span class="keyword">rec</span> x = <span class="keyword">lazy</span>(<span class="keyword">lazy</span>(...(<span class="keyword">lazy</span> x)))</code> are accepted by the type-checker and lead, when forced, to ill-formed values that trigger infinite loops in the garbage collector and other parts of the run-time system. Without the <code class="code">-rectypes</code> option, such ill-founded recursive definitions are rejected by the type-checker.<br> </div> <pre><span id="EXCEPTIONUndefined"><span class="keyword">exception</span> Undefined</span></pre> <pre><span id="VALforce"><span class="keyword">val</span> force</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> 'a</code></pre><div class="info "> <code class="code">force x</code> forces the suspension <code class="code">x</code> and returns its result. If <code class="code">x</code> has already been forced, <code class="code"><span class="constructor">Lazy</span>.force x</code> returns the same value again without recomputing it. If it raised an exception, the same exception is raised again. Raise <code class="code"><span class="constructor">Undefined</span></code> if the forcing of <code class="code">x</code> tries to force <code class="code">x</code> itself recursively.<br> </div> <pre><span id="VALforce_val"><span class="keyword">val</span> force_val</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> 'a</code></pre><div class="info "> <code class="code">force_val x</code> forces the suspension <code class="code">x</code> and returns its result. If <code class="code">x</code> has already been forced, <code class="code">force_val x</code> returns the same value again without recomputing it. Raise <code class="code"><span class="constructor">Undefined</span></code> if the forcing of <code class="code">x</code> tries to force <code class="code">x</code> itself recursively. If the computation of <code class="code">x</code> raises an exception, it is unspecified whether <code class="code">force_val x</code> raises the same exception or <code class="code"><span class="constructor">Undefined</span></code>.<br> </div> <pre><span id="VALfrom_fun"><span class="keyword">val</span> from_fun</span> : <code class="type">(unit -> 'a) -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info "> <code class="code">from_fun f</code> is the same as <code class="code"><span class="keyword">lazy</span> (f ())</code> but slightly more efficient.<br> <b>Since</b> 4.00.0<br> </div> <pre><span id="VALfrom_val"><span class="keyword">val</span> from_val</span> : <code class="type">'a -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info "> <code class="code">from_val v</code> returns an already-forced suspension of <code class="code">v</code>. This is for special purposes only and should not be confused with <code class="code"><span class="keyword">lazy</span> (v)</code>.<br> <b>Since</b> 4.00.0<br> </div> <pre><span id="VALis_val"><span class="keyword">val</span> is_val</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> bool</code></pre><div class="info "> <code class="code">is_val x</code> returns <code class="code"><span class="keyword">true</span></code> if <code class="code">x</code> has already been forced and did not raise an exception.<br> <b>Since</b> 4.00.0<br> </div> <pre><span id="VALlazy_from_fun"><span class="keyword">val</span> lazy_from_fun</span> : <code class="type">(unit -> 'a) -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info "> <span class="warning">Deprecated.</span>synonym for <code class="code">from_fun</code>.<br> </div> <pre><span id="VALlazy_from_val"><span class="keyword">val</span> lazy_from_val</span> : <code class="type">'a -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info "> <span class="warning">Deprecated.</span>synonym for <code class="code">from_val</code>.<br> </div> <pre><span id="VALlazy_is_val"><span class="keyword">val</span> lazy_is_val</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> bool</code></pre><div class="info "> <span class="warning">Deprecated.</span>synonym for <code class="code">is_val</code>.<br> </div> </body></html>