You are better to use simple typeclasses. It depends on what you are trying to do, but when I want an open type, I use classes + type families.<br><br><br><div class="gmail_quote">2011/3/18 Stephen Tetley <span dir="ltr">&lt;<a href="mailto:stephen.tetley@gmail.com">stephen.tetley@gmail.com</a>&gt;</span><br>

<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">On 18 March 2011 13:31, Grigory Sarnitskiy &lt;<a href="mailto:sargrigory@ya.ru">sargrigory@ya.ru</a>&gt; wrote:<br>


<br>
&gt; Anyway, a new question arose.  If I have already declared a type, can I add new constructors to it from other modules?<br>
&gt;<br>
&gt; Maybe there are some GHC extensions to solve both these problems.<br>
<br>
</div>&quot;no can do&quot;.<br>
<br>
There are ways to encode extensible types (e.g the &quot;finally tagless&quot;<br>
sytle), but on balance you are better to design extensibility for<br>
functions - easy to add more functions - than make your code much more<br>
complicated so it can be extensible for types.<br>
<br>
Parser combinators and pretty print combinators are great and largely<br>
simple examples of extensibility with functions.<br>
<div><div></div><div class="h5"><br>
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