t.Sum) ~f:int_of_string [&quot;1&quot;;&quot;2&quot;;&quot;3&quot;;&quot;4&quot;];;
- : int = 10</code></pre></dd></dl><dl><dt class="spec value" id="val-fold_left"><a href="#val-fold_left" class="anchor"></a><code><span class="keyword">val</span> fold_left : <span>f:<span>(<span class="type-var">'b</span> <span>&#45;&gt;</span> <span class="type-var">'a</span> <span>&#45;&gt;</span> <span class="type-var">'b</span>)</span></span> <span>&#45;&gt;</span> <span>init:<span class="type-var">'b</span></span> <sp