Commit 57b1d54a authored by Ian Lynagh's avatar Ian Lynagh
Browse files

Document the Num superclass divergence from H98/H2010

parent 804108f0
...@@ -149,6 +149,39 @@ main = do args <- getArgs ...@@ -149,6 +149,39 @@ main = do args <- getArgs
<title>Numbers, basic types, and built-in classes</title> <title>Numbers, basic types, and built-in classes</title>
<variablelist> <variablelist>
<term>Num superclasses</term>
The <literal>Num</literal> class does not have
<literal>Show</literal> or <literal>Eq</literal>
You can make code that works with both
Haskell98/Haskell2010 and GHC by:
Whenever you make a <literal>Num</literal> instance
of a type, also make <literal>Show</literal> and
<literal>Eq</literal> instances, and
Whenever you give a function, instance or class a
<literal>Num t</literal> constraint, also give it
<literal>Show t</literal> and
<literal>Eq t</literal> constraints.
<varlistentry> <varlistentry>
<term>Multiply-defined array elements&mdash;not checked:</term> <term>Multiply-defined array elements&mdash;not checked:</term>
<listitem> <listitem>
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