n need to
    concatenate sequences, and using lists for this purpose is expensive. This
    module provides routines to manage such lists more efficiently. In this
    model, we never do cons or append explicitly. Instead we maintain
    the elements of the list in a special data structure. Routines are provided
    to convert to/from ordinary lists, and carry out common list operations.<br>
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<br><code><span id="TYPEclist"><span class="keyword">type</span> <code class="type">'a</code> clis