diff options
Diffstat (limited to 'docs/users_guide/glasgow_exts.xml')
| -rw-r--r-- | docs/users_guide/glasgow_exts.xml | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml index de69b60063..26fff9a046 100644 --- a/docs/users_guide/glasgow_exts.xml +++ b/docs/users_guide/glasgow_exts.xml @@ -5000,9 +5000,13 @@ Type splices are not implemented, and neither are pattern splices or quotations. </para></listitem> <listitem><para> - Furthermore, you can only run a function at compile time if it is imported + You can only run a function at compile time if it is imported from another module <emphasis>that is not part of a mutually-recursive group of modules - that includes the module currently being compiled</emphasis>. For example, when compiling module A, + that includes the module currently being compiled</emphasis>. Furthermore, all of the modules of + the mutually-recursive group must be reachable by non-SOURCE imports from the module where the + splice is to be run.</para> + <para> + For example, when compiling module A, you can only run Template Haskell functions imported from B if B does not import A (directly or indirectly). The reason should be clear: to run B we must compile and run A, but we are currently type-checking A. </para></listitem> @@ -6374,14 +6378,14 @@ data T = T {-# UNPACK #-} !(Int,Int) <para>will store the two <literal>Int</literal>s directly in the <function>T</function> constructor, by flattening the pair. - Multi-level unpacking is also supported:</para> + Multi-level unpacking is also supported: <programlisting> data T = T {-# UNPACK #-} !S data S = S {-# UNPACK #-} !Int {-# UNPACK #-} !Int </programlisting> - <para>will store two unboxed <literal>Int#</literal>s + will store two unboxed <literal>Int#</literal>s directly in the <function>T</function> constructor. The unpacker can see through newtypes, too.</para> @@ -6395,6 +6399,15 @@ data S = S {-# UNPACK #-} !Int {-# UNPACK #-} !Int constructor field.</para> </sect2> + <sect2 id="source-pragma"> + <title>SOURCE pragma</title> + + <indexterm><primary>SOURCE</primary></indexterm> + <para>The <literal>{-# SOURCE #-}</literal> pragma is used only in <literal>import</literal> declarations, + to break a module loop. It is described in detail in <xref linkend="mutual-recursion"/>. + </para> +</sect2> + </sect1> <!-- ======================= REWRITE RULES ======================== --> |