>&#45;&gt;</span> <span>unit Lwt.t</span>)</span></span> <span>&#45;&gt;</span> <span>?&#8288;step:float</span> <span>&#45;&gt;</span> <span>react:<span>(<span class="type-var">'a</span> <span>&#45;&gt;</span> <span><span class="type-var">'e</span> list</span> <span>&#45;&gt;</span> <span class="type-var">'b</span> <span>&#45;&gt;</span> <span><span><span>(<span class="type-var">'c</span>, <span class="type-var">'d</span>)</span> Stdlib.result</span> Lwt.t</span>)</span></span> <span>&#45;&gt;</span> <span