l</span> concat : <span><span><span class="type-var">'a</span> list</span> list</span> <span>&#45;&gt;</span> <span><span class="type-var">'a</span> list</span></code></dt><dt class="spec value" id="val-flatten"><a href="#val-flatten" class="anchor"></a><code><span class="keyword">val</span> flatten : <span><span><span class="type-var">'a</span> list</span> list</span> <span>&#45;&gt;</span> <span><span class="type-var">'a</span> list</span></code></dt><dt class="spec value" id="val-iter"><a href="#val-iter