ing a <span 
class="pcrr7t-">newtype</span> declaration. For example, stacks
can be defined with lists:
     <div class="quote">
                                                                                   

                                                                                   
     <div class="verbatim" id="verbatim-105">
&#x00A0;&#x00A0;module&#x00A0;Stack(&#x00A0;StkType,&#x00A0;push,&#x00A0;pop,&#x00A0;empty&#x00A0;)&#x00A0;where
&#x00A0;<br />&#x00A0;&#x00A0;&#x00A0;&#x00A0;newtype&#