Hi, buddies. I am a newbie on Haskell. Recently I want to implement a simple Lattice in Haskell, but I met some difficulties.<br>Scrap of the code is as below, but I met syntax error:<br><br>&gt;&nbsp; class Lattice e where<br>
&gt;&nbsp; &nbsp;&nbsp;&nbsp; join :: e -&gt; e -&gt; e<br>&gt;&nbsp; &nbsp;&nbsp;&nbsp; meet :: e -&gt; e -&gt; e<br>&gt;&nbsp; <br>&gt;&nbsp; &nbsp;&nbsp;&nbsp; -- associative law<br>&gt;&nbsp; &nbsp;&nbsp;&nbsp; join x (join y z) = join (join x y) z<br>&gt;&nbsp; &nbsp;&nbsp;&nbsp; join (join x y) z = join x (join y z)<br>
<br>The main problem is that mathematic equations is bi-directed, but in Haskell the pattern matching is only in one direction -<br>from left to right. And only variables and constructors could be occur in the right side of the pattern matching.
<br><br>Seems mathematic axioms and pattern matching are different things.<br><br>So how could I rewrite the equations to pattern matching? Which technique should I learn?<br><br>Thanks for your help.<br><br>Regards,<br>Mingli
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