interface file will be put in <literal>src/A/B/C.hi</literal>
and the object file in <literal>src/A/B/C.o</literal>.</para>
- <para>Note that it is reasonable to have a module
+ <para>For any module that is imported, GHC requires that the
+ name of the module in the import statement exactly matches the
+ name of the module in the interface file (or source file) found
+ using the strategy specified in <xref linkend="search-path">.
+ This means that for most modules, the source file name should
+ match the module name.</para>
+
+ <para>However, note that it is reasonable to have a module
<literal>Main</literal> in a file named
<filename>foo.hs</filename>, but this only works because GHC
never needs to search for the interface for module
<literal>Main</literal> (because it is never imported). It is
therefore possible to have several <literal>Main</literal>
modules in separate source files in the same directory, and GHC
- will not get confused. For modules other than
- <literal>Main</literal>, it is strongly recommended that you
- name the source file after the module name, replacing dots with
- slashes in hierarchical module names.</para>
+ will not get confused.</para>
<para>In batch compilation mode, the name of the object file can
also be overriden using the <option>-o</option> option, and the
<literal>instances</literal> or derive them automatically.
</para>
</listitem>
+
+<listitem> <para>For <literal>data</literal> or <literal>newtype</literal> declaration, you may omit all
+the constructors, by omitting the '=' and everything that follows it:
+<ProgramListing>
+module A where
+ data TA
+</ProgramListing>
+ In a <emphasis>source</emphasis> program
+ this would declare TA to have no constructors (a GHC extension: see <xref linkend="nullary-types">),
+ but in an hi-boot file it means "I don't know or care what the construtors are".
+ This is the most common form of data type declaration, because it's easy to get right.</para>
+ <para>
+ You <emphasis>can</emphasis> also write out the constructors but, if you do so, you must write
+ it out precisely as in its real definition.
+ It is especially delicate if you use a strictness annotation "!",
+ with or without an <literal>{-# UNPACK #-}</literal> pragma. In a source file
+ GHC may or may not choose to unbox the argument, but in an hi-boot file it's
+ assumed that you express the <emphasis>outcome</emphasis> of this decision.
+ (So in the cases where GHC decided not to unpack, you must not use the pragma.)
+ Tread with care.</para>
+ <para>
+ Regardless of whether you write the constructors, you must write all the type parameters,
+ <emphasis>including their kinds</emphasis>
+ if they are not '*'. (You can give explicit kinds in source files too (<xref linkend="sec-kinding">),
+ but you <emphasis>must</emphasis> do so in hi-boot files.)</para>
+ </listitem>
+
+<listitem> <para>For <literal>class</literal> declaration, you may not specify any class
+operations. We could lift this restriction if it became tiresome.</para>
+</listitem>
</itemizedlist>
<para>Notice that we only put the declaration for the newtype
not the signature for <Function>f</Function>, since
<Function>f</Function> isn't used by <literal>B</literal>.</para>
- <para>If you want an <literal>hi-boot</literal> file to export a
- data type, but you don't want to give its constructors (because
- the constructors aren't used by the SOURCE-importing module),
- you can write simply:</para>
-
-<ProgramListing>
-module A where
-data TA
-</ProgramListing>
-
- <para>(You must write all the type parameters, but leave out the
- '=' and everything that follows it.)</para>
</sect2>
projects / ghc-hetmet.git / blobdiff