<sect1 id="vs-Haskell-defn">
<title>Haskell 98 vs. Glasgow Haskell: language non-compliance
</title>
-
+
<indexterm><primary>GHC vs the Haskell 98 language</primary></indexterm>
<indexterm><primary>Haskell 98 language vs GHC</primary></indexterm>
<sect2 id="haskell98-divergence">
<title>Divergence from Haskell 98</title>
-
-
+
+
<sect3 id="infelicities-lexical">
<title>Lexical syntax</title>
-
- <itemizedlist>
- <listitem>
- <para>The Haskell report specifies that programs may be
- written using Unicode. GHC only accepts the ISO-8859-1
- character set at the moment.</para>
- </listitem>
+ <itemizedlist>
<listitem>
<para>Certain lexical rules regarding qualified identifiers
are slightly different in GHC compared to the Haskell
</listitem>
</itemizedlist>
</sect3>
-
+
<sect3 id="infelicities-syntax">
<title>Context-free syntax</title>
-
+
<itemizedlist>
<listitem>
<para>GHC is a little less strict about the layout rule when used
<sect3 id="infelicities-decls">
<title>Declarations and bindings</title>
- <para>None known.</para>
+ <para>GHC's typechecker makes all pattern bindings monomorphic
+ by default; this behaviour can be disabled with
+ <option>-XNoMonoPatBinds</option>. See <xref
+ linkend="options-language" />.</para>
</sect3>
-
+
<sect3 id="infelicities-Modules">
<title>Module system and interface files</title>
-
- <para>None known.</para>
+
+ <para>GHC requires the use of <literal>hs-boot</literal>
+ files to cut the recursive loops among mutually recursive modules
+ as described in <xref linkend="mutual-recursion"/>. This more of an infelicity
+ than a bug: the Haskell Report says
+ (<ulink url="http://haskell.org/onlinereport/modules.html#sect5.7">Section 5.7</ulink>) "Depending on the Haskell
+ implementation used, separate compilation of mutually
+ recursive modules may require that imported modules contain
+ additional information so that they may be referenced before
+ they are compiled. Explicit type signatures for all exported
+ values may be necessary to deal with mutual recursion. The
+ precise details of separate compilation are not defined by
+ this Report."
+
+ </para>
+
</sect3>
<sect3 id="infelicities-numbers">
</listitem>
</varlistentry>
</variablelist>
-
+
</sect3>
<sect3 id="infelicities-Prelude">
alphabetic by <literal>isAlpha</literal>.</para>
</listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><literal>hGetContents</literal></term>
+ <listitem>
+ <para>
+ Lazy I/O throws an exception if an error is
+ encountered, in contrast to the Haskell 98 spec which
+ requires that errors are discarded (see Section 21.2.2
+ of the Haskell 98 report). The exception thrown is
+ the usual IO exception that would be thrown if the
+ failing IO operation was performed in the IO monad, and can
+ be caught by <literal>System.IO.Error.catch</literal>
+ or <literal>Control.Exception.catch</literal>.
+ </para>
+ </listitem>
+ </varlistentry>
</variablelist>
</sect3>
</sect2>
the <literal>Int</literal> type.</para>
<para>The <literal>fromInteger</literal><indexterm><primary><literal>fromInteger</literal></primary>
- </indexterm>function (and hence
+ </indexterm> function (and hence
also <literal>fromIntegral</literal><indexterm><primary><literal>fromIntegral</literal></primary>
</indexterm>) is a special case when
converting to <literal>Int</literal>. The value of
<para>Negative literals, such as <literal>-3</literal>, are
- specified by (a careful reading of) the Haskell Report as
+ specified by (a careful reading of) the Haskell Report as
meaning <literal>Prelude.negate (Prelude.fromInteger 3)</literal>.
So <literal>-2147483648</literal> means <literal>negate (fromInteger 2147483648)</literal>.
Since <literal>fromInteger</literal> takes the lower 32 bits of the representation,
</listitem>
</varlistentry>
</variablelist>
-
+
</sect2>
+
+ <sect2 id="ffi-divergence">
+ <title>Divergence from the FFI specification</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><literal>hs_init()</literal> not allowed
+ after <literal>hs_exit()</literal></term>
+ <listitem>
+ <para>The FFI spec requires the implementation to support
+ re-initialising itself after being shut down
+ with <literal>hs_exit()</literal>, but GHC does not
+ currently support that.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </sect2>
+
</sect1>
</listitem>
<listitem>
- <para>GHC does not allow you to have a data type with a context
+ <para>GHC does not allow you to have a data type with a context
that mentions type variables that are not data type parameters.
For example:
<programlisting>
using the standard way to encode recursion via a data type:</para>
<programlisting>
data U = MkU (U -> Bool)
-
+
russel :: U -> Bool
russel u@(MkU p) = not $ p u
-
+
x :: Bool
x = russel (MkU russel)
</programlisting>
the problem would impose an extra overhead on every
compilation. So the bug remains un-fixed. There is more
background in <ulink
- url="http://research.microsoft.com/~simonpj/Papers/inlining">
+ url="http://research.microsoft.com/~simonpj/Papers/inlining/">
Secrets of the GHC inliner</ulink>.</para>
</listitem>
module (whatever that is).</para>
</listitem>
- <listitem>
+ <listitem>
<para>On Windows, there's a GNU ld/BFD bug
whereby it emits bogus PE object files that have more than
0xffff relocations. When GHCi tries to load a package affected by this
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