f</span>, <span class="type-var">'arg_payload</span>)</span> <a href="index.html#type-one_arg">one_arg</a></span></code></dt><dd><p>Captures one arg Var. Fails with an internal error if the expression is not a Var</p></dd></dl><dl><dt class="spec value" id="val-($+)"><a href="#val-($+)" class="anchor"></a><code><span class="keyword">val</span> ($+) : <span><span>(<span class="type-var">'context</span>, <span class="type-var">'f_in</span>, <span class="type-var">'f_proc_out</span>, <span class="type-var"