has been specified, then the object filename is
<replaceable>dir</replaceable>/<replaceable>mod</replaceable>.<replaceable>osuf</replaceable>,
where <replaceable>mod</replaceable> is the module name with
- dots replaced by slashes. GHC will silently create the necessary directory
+ dots replaced by slashes. GHC will silently create the necessary directory
structure underneath <replaceable>dir</replaceable>, if it does not
- already exist.</para>
+ already exist.</para>
</listitem>
</itemizedlist>
<para>If you use <command>ghc --make</command> and you don't
use the <option>-o</option>, the name GHC will choose
for the executable will be based on the name of the file
- containing the module <literal>Main</literal>.
+ containing the module <literal>Main</literal>.
Note that with GHC the <literal>Main</literal> module doesn't
have to be put in file <filename>Main.hs</filename>.
Thus both
</varlistentry>
</variablelist>
</sect2>
-
+
<sect2 id="keeping-intermediates">
<title>Keeping Intermediate Files</title>
<indexterm><primary>intermediate files, saving</primary>
This section explains how.</para>
<para>Every cycle in the module import graph must be broken by a <filename>hs-boot</filename> file.
- Suppose that modules <filename>A.hs</filename> and <filename>B.hs</filename> are Haskell source files,
+ Suppose that modules <filename>A.hs</filename> and <filename>B.hs</filename> are Haskell source files,
thus:
<programlisting>
module A where
import B( TB(..) )
-
+
newtype TA = MkTA Int
-
+
f :: TB -> TA
f (MkTB x) = MkTA x
module B where
import {-# SOURCE #-} A( TA(..) )
-
+
data TB = MkTB !Int
-
+
g :: TA -> TB
g (MkTA x) = MkTB x
</programlisting>
<programlisting>
ghc -c A.hs-boot
</programlisting>
-When a hs-boot file <filename>A.hs-boot</filename>
+When a hs-boot file <filename>A.hs-boot</filename>
is compiled, it is checked for scope and type errors.
When its parent module <filename>A.hs</filename> is compiled, the two are compared, and
an error is reported if the two are inconsistent.
</para></listitem>
-
+
<listitem>
<para> Just as compiling <filename>A.hs</filename> produces an
interface file <filename>A.hi</filename>, and an object file
<command>ghc -M</command> will report an error if a cycle is found.
</para></listitem>
- <listitem><para> A module <literal>M</literal> that is
+ <listitem><para> A module <literal>M</literal> that is
<literal>{-# SOURCE #-}</literal>-imported in a program will usually also be
ordinarily imported elsewhere. If not, <command>ghc --make</command>
automatically adds <literal>M</literal> to the set of modules it tries to
<para>A hs-boot file is written in a subset of Haskell:
<itemizedlist>
<listitem><para> The module header (including the export list), and import statements, are exactly as in
-Haskell, and so are the scoping rules.
+Haskell, and so are the scoping rules.
Hence, to mention a non-Prelude type or class, you must import it.</para></listitem>
-
+
<listitem><para> There must be no value declarations, but there can be type signatures for
values. For example:
<programlisting>
</para></listitem>
<listitem><para> Fixity declarations are exactly as in Haskell.</para></listitem>
<listitem><para> Type synonym declarations are exactly as in Haskell.</para></listitem>
-<listitem><para> A data type declaration can either be given in full, exactly as in Haskell, or it
+<listitem><para> A data type declaration can either be given in full, exactly as in Haskell, or it
can be given abstractly, by omitting the '=' sign and everything that follows. For example:
<programlisting>
data T a b
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.</para>
<para>
- If you do not write out the constructors, you may need to give a kind
+ If you do not write out the constructors, you may need to give a kind
annotation (<xref linkend="kinding"/>), to tell
GHC the kind of the type variable, if it is not "*". (In source files, this is worked out
from the way the type variable is used in the constructors.) For example:
brought up to date. To bring it up to date,
<literal>make</literal> looks for a rule to do so; one of the
preceding suffix rules does the job nicely. These dependencies
- can be generated automatically by <command>ghc</command>; see
+ can be generated automatically by <command>ghc</command>; see
<xref linkend="makefile-dependencies"/></para>
</sect2>
<filename>Makefile</filename>.</para>
<para>In general, <command>ghc -M Foo</command> does the following.
- For each module <literal>M</literal> in the set
+ For each module <literal>M</literal> in the set
<literal>Foo</literal> plus all its imports (transitively),
it adds to the Makefile:
<itemizedlist>
(See <xref linkend="mutual-recursion"/> for details of
<literal>hi-boot</literal> style interface files.)
</para></listitem>
- </itemizedlist>
+ </itemizedlist>
If <literal>M</literal> imports multiple modules, then there will
be multiple lines with <filename>M.o</filename> as the
target.</para>
be a disaster in practice, so GHC tries to be clever. </para>
<para>In particular, if an instance declaration is in the same module as the definition
-of any type or class mentioned in the <emphasis>head</emphasis> of the instance declaration
+of any type or class mentioned in the <emphasis>head</emphasis> of the instance declaration
(the part after the “<literal>=></literal>”; see <xref linkend="instance-rules"/>), then
GHC has to visit that interface file anyway. Example:</para>
<programlisting>
least one <emphasis>orphan rule</emphasis>.</para> </listitem>
<listitem><para> An instance declaration in a module M is an <emphasis>orphan instance</emphasis> if
- <indexterm><primary>orphan instance</primary></indexterm>
-<itemizedlist>
+ <indexterm><primary>orphan instance</primary></indexterm>
+<itemizedlist>
<listitem><para>
The class of the instance declaration is not declared in M, and
</para></listitem>
</para></listitem>
</itemizedlist>
</para>
- <para> Only the instance head
+ <para> Only the instance head
counts. In the example above, it is not good enough for C's declaration
to be in module A; it must be the declaration of D or T.</para>
</listitem>
-<para>If you use the flag <option>-fwarn-orphans</option>, GHC will warn you
+<para>If you use the flag <option>-fwarn-orphans</option>, GHC will warn you
if you are creating an orphan module.
-Like any warning, you can switch the warning off with <option>-fno-warn-orphans</option>,
+Like any warning, you can switch the warning off with <option>-fno-warn-orphans</option>,
and <option>-Werror</option>
will make the compilation fail if the warning is issued.
</para>
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