-<Chapter id="using-GHC">
-<title>Using GHC
-</title>
+<chapter id="using-ghc">
+ <title>Using GHC</title>
-<para>
-<IndexTerm><Primary>GHC, using</Primary></IndexTerm>
-<IndexTerm><Primary>using GHC</Primary></IndexTerm>
-GHC is a command-line compiler: in order to compile a Haskell program,
-GHC must be invoked on the source file(s) by typing a command to the
-shell. The steps involved in compiling a program can be automated
-using the <command>make</command> tool (this is especially useful if the program
-consists of multiple source files which depend on each other). This
-section describes how to use GHC from the command-line.
-</para>
+ <indexterm><primary>GHC, using</primary></indexterm>
+ <indexterm><primary>using GHC</primary></indexterm>
-<Sect1 id="command-line-structure">
-<title>Overall command-line structure
-</title>
-
-<para>
-<IndexTerm><Primary>structure, command-line</Primary></IndexTerm>
-<IndexTerm><Primary>command-line structure</Primary></IndexTerm>
-</para>
+ <para>GHC can work in one of three “modes”:</para>
-<para>
-An invocation of GHC takes the following form:
-</para>
+ <variablelist>
+ <varlistentry>
+ <term><cmdsynopsis><command>ghc</command>
+ <arg choice=plain>––interactive</arg>
+ </cmdsynopsis></term>
+ <indexterm><primary>interactive mode</primary>
+ </indexterm>
+ <indexterm><primary>ghci</primary>
+ </indexterm>
+ <listitem>
+ <para>Interactive mode, which is also available as
+ <command>ghci</command>. Interactive mode is described in
+ more detail in <xref linkend="ghci">.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><cmdsynopsis><command>ghc</command>
+ <arg choice=plain>––make</arg>
+ </cmdsynopsis></term>
+ <indexterm><primary>make mode</primary>
+ </indexterm>
+ <indexterm><primary><option>––make</option></primary>
+ </indexterm>
+ <listitem>
+ <para>In this mode, GHC will build a multi-module Haskell
+ program automatically, figuring out dependencies for itself.
+ If you have a straightforward Haskell program, this is likely
+ to be much easier, and faster, than using
+ <command>make</command>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><cmdsynopsis>
+ <command>ghc</command>
+ <group>
+ <arg>-E</arg>
+ <arg>-C</arg>
+ <arg>-S</arg>
+ <arg>-c</arg>
+ </group>
+ </cmdsynopsis></term>
+ <indexterm><primary><option>-E</option></primary></indexterm>
+ <indexterm><primary><option>-C</option></primary></indexterm>
+ <indexterm><primary><option>-S</option></primary></indexterm>
+ <indexterm><primary><option>-c</option></primary></indexterm>
+ <listitem>
+ <para>This is the traditional batch-compiler mode, in which
+ GHC can compile source files one at a time, or link objects
+ together into an executable.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <sect1>
+ <title>Options overview</title>
+
+ <para>GHC's behaviour is controlled by
+ <firstterm>options</firstterm>, which for historical reasons are
+ also sometimes referred to as command-line flags or arguments.
+ Options can be specified in three ways:</para>
-<para>
+ <sect2>
+ <title>Command-line arguments</title>
+
+ <indexterm><primary>structure, command-line</primary></indexterm>
+ <indexterm><primary>command-line</primary><secondary>arguments</secondary></indexterm>
+ <indexterm><primary>arguments</primary><secondary>command-line</secondary></indexterm>
+
+ <para>An invocation of GHC takes the following form:</para>
<Screen>
ghc [argument...]
</Screen>
-</para>
+ <para>Command-line arguments are either options or file names.</para>
+
+ <para>Command-line options begin with <literal>-</literal>.
+ They may <emphasis>not</emphasis> be grouped:
+ <option>-vO</option> is different from <option>-v -O</option>.
+ Options need not precede filenames: e.g., <literal>ghc *.o -o
+ foo</literal>. All options are processed and then applied to
+ all files; you cannot, for example, invoke <literal>ghc -c -O1
+ Foo.hs -O2 Bar.hs</literal> to apply different optimisation
+ levels to the files <filename>Foo.hs</filename> and
+ <filename>Bar.hs</filename>.</para>
+ </sect2>
-<para>
-Command-line arguments are either options or file names.
-</para>
+ <Sect2 id="source-file-options">
+ <title>Command line options in source files</title>
+
+ <indexterm><primary>source-file options</primary></indexterm>
+
+ <para>Sometimes it is useful to make the connection between a
+ source file and the command-line options it requires quite
+ tight. For instance, if a Haskell source file uses GHC
+ extensions, it will always need to be compiled with the
+ <option>-fglasgow-exts</option> option. Rather than maintaining
+ the list of per-file options in a <filename>Makefile</filename>,
+ it is possible to do this directly in the source file using the
+ <literal>OPTIONS</literal> pragma <indexterm><primary>OPTIONS
+ pragma</primary></indexterm>:</para>
-<para>
-Command-line options begin with <literal>-</literal>. They may <emphasis>not</emphasis> be
-grouped: <option>-vO</option> is different from <option>-v -O</option>. Options need not
-precede filenames: e.g., <command>ghc *.o -o foo</command>. All options are
-processed and then applied to all files; you cannot, for example, invoke
-<command>ghc -c -O1 Foo.hs -O2 Bar.hs</command> to apply different optimisation
-levels to the files <filename>Foo.hs</filename> and <filename>Bar.hs</filename>. For conflicting
-options, e.g., <option>-c -S</option>, we reserve the right to do anything we
-want. (Usually, the last one applies.)
-</para>
+<ProgramListing>
+{-# OPTIONS -fglasgow-exts #-}
+module X where
+...
+</ProgramListing>
+
+ <para><literal>OPTIONS</literal> pragmas are only looked for at
+ the top of your source files, upto the first
+ (non-literate,non-empty) line not containing
+ <literal>OPTIONS</literal>. Multiple <literal>OPTIONS</literal>
+ pragmas are recognised. Note that your command shell does not
+ get to the source file options, they are just included literally
+ in the array of command-line arguments the compiler driver
+ maintains internally, so you'll be desperately disappointed if
+ you try to glob etc. inside <literal>OPTIONS</literal>.</para>
+
+ <para>NOTE: the contents of OPTIONS are prepended to the
+ command-line options, so you <emphasis>do</emphasis> have the
+ ability to override OPTIONS settings via the command
+ line.</para>
+
+ <para>It is not recommended to move all the contents of your
+ Makefiles into your source files, but in some circumstances, the
+ <literal>OPTIONS</literal> pragma is the Right Thing. (If you
+ use <option>-keep-hc-file-too</option> and have OPTION flags in
+ your module, the OPTIONS will get put into the generated .hc
+ file).</para>
+ </sect2>
-</Sect1>
+ <sect2>
+ <title>Setting options in GHCi</title>
-<Sect1 id="file-suffixes">
-<title>Meaningful file suffixes
-</title>
+ <para>Options may also be modified from within GHCi, using the
+ <literal>:set</literal> command. See <xref linkend="ghci-set">
+ for more details.</para>
+ </sect2>
+ </sect1>
+
+ <sect1 id="static-dynamic-flags">
+ <title>Static vs. Dynamic options</title>
+ <indexterm><primary>static</primary><secondary>options</secondary>
+ </indexterm>
+ <indexterm><primary>dynamic</primary><secondary>options</secondary>
+ </indexterm>
+
+ <para>Each of GHC's command line options is classified as either
+ <firstterm>static</firstterm> or <firstterm>dynamic</firstterm>.
+ A static flag may only be specified on the command line, whereas a
+ dynamic flag may also be given in an <literal>OPTIONS</literal>
+ pragma in a source file or set from the GHCi command-line with
+ <literal>:set</literal>.</para>
+
+ <para>As a rule of thumb, all the language options are dynamic, as
+ are the warning options and the debugging options. The rest are
+ static, with the notable exceptions of <option>-v</option>,
+ <option>-cpp</option>, <option>-fasm</option>,
+ <option>-fvia-C</option>, and <option>-#include</option>.
+
+ The flag reference tables (<xref linkend="flag-reference">) lists
+ the status of each flag.</para>
+ </sect1>
-<para>
-<IndexTerm><Primary>suffixes, file</Primary></IndexTerm>
-<IndexTerm><Primary>file suffixes for GHC</Primary></IndexTerm>
-</para>
+ <sect1 id="file-suffixes">
+ <title>Meaningful file suffixes</title>
-<para>
-File names with “meaningful” suffixes (e.g., <filename>.lhs</filename> or <filename>.o</filename>)
-cause the “right thing” to happen to those files.
-</para>
+ <indexterm><primary>suffixes, file</primary></indexterm>
+ <indexterm><primary>file suffixes for GHC</primary></indexterm>
-<para>
-<VariableList>
+ <para>File names with “meaningful” suffixes (e.g.,
+ <filename>.lhs</filename> or <filename>.o</filename>) cause the
+ “right thing” to happen to those files.</para>
-<VarListEntry>
-<Term><filename>.lhs</filename>:</Term>
-<ListItem>
-<para>
-<IndexTerm><Primary>lhs suffix</Primary></IndexTerm>
-A “literate Haskell” module.
-</para>
-</ListItem>
-</VarListEntry>
-<VarListEntry>
-<Term><filename>.hs</filename>:</Term>
-<ListItem>
-<para>
-A not-so-literate Haskell module.
-</para>
-</ListItem>
-</VarListEntry>
-<VarListEntry>
-<Term><filename>.hi</filename>:</Term>
-<ListItem>
-<para>
-A Haskell interface file, probably compiler-generated.
-</para>
-</ListItem>
-</VarListEntry>
-<VarListEntry>
-<Term><filename>.hc</filename>:</Term>
-<ListItem>
-<para>
-Intermediate C file produced by the Haskell compiler.
-</para>
-</ListItem>
-</VarListEntry>
-<VarListEntry>
-<Term><filename>.c</filename>:</Term>
-<ListItem>
-<para>
-A C file not produced by the Haskell compiler.
-</para>
-</ListItem>
-</VarListEntry>
-<VarListEntry>
-<Term><filename>.s</filename>:</Term>
-<ListItem>
-<para>
-An assembly-language source file, usually
-produced by the compiler.
-</para>
-</ListItem>
-</VarListEntry>
-<VarListEntry>
-<Term><filename>.o</filename>:</Term>
-<ListItem>
-<para>
-An object file, produced by an assembler.
-</para>
-</ListItem>
-</VarListEntry>
-</VariableList>
-</para>
+ <variablelist>
-<para>
-Files with other suffixes (or without suffixes) are passed straight
-to the linker.
-</para>
+ <varlistentry>
+ <term><filename>.lhs</filename></term>
+ <indexterm><primary><literal>lhs</literal> suffix</primary></indexterm>
+ <listitem>
+ <para>A “literate Haskell” module.</para>
+ </listitem>
+ </varlistentry>
-</Sect1>
+ <varlistentry>
+ <term><filename>.hs</filename></term>
+ <listitem>
+ <para>A not-so-literate Haskell module.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>.hi</filename></term>
+ <listitem>
+ <para>A Haskell interface file, probably
+ compiler-generated.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>.hc</filename></term>
+ <listitem>
+ <para>Intermediate C file produced by the Haskell
+ compiler.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>.c</filename></term>
+ <listitem>
+ <para>A C file not produced by the Haskell
+ compiler.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>.s</filename></term>
+ <listitem>
+ <para>An assembly-language source file, usually produced by
+ the compiler.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><filename>.o</filename></term>
+ <listitem>
+ <para>An object file, produced by an assembler.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>Files with other suffixes (or without suffixes) are passed
+ straight to the linker.</para>
+
+ </sect1>
<sect1 id="options-help">
<title>Help and verbosity options</title>
<variablelist>
<varlistentry>
- <term><literal>-help</literal></term>
- <term><literal>-?</literal></term>
- <indexterm><primary><literal>-?</literal></primary></indexterm>
- <indexterm><primary><literal>-help</literal></primary></indexterm>
+ <term><option>––help</option></term>
+ <term><option>-?</option></term>
+ <indexterm><primary><option>-?</option></primary></indexterm>
+ <indexterm><primary><option>––help</option></primary></indexterm>
<listitem>
<para>Cause GHC to spew a long usage message to standard
output and then exit.</para>
</varlistentry>
<varlistentry>
- <term><literal>-v</literal></term>
- <indexterm><primary><literal>-v</literal></primary></indexterm>
+ <term><option>-v</option></term>
+ <indexterm><primary><option>-v</option></primary></indexterm>
<listitem>
<para>The <option>-v</option> option makes GHC
<emphasis>verbose</emphasis>: it reports its version number
</varlistentry>
<varlistentry>
- <term><literal>-v</literal><replaceable>n</replaceable></term>
+ <term><option>-v</option><replaceable>n</replaceable></term>
<indexterm><primary><option>-v</option></primary></indexterm>
<listitem>
<para>To provide more control over the compiler's verbosity,
<variablelist>
<varlistentry>
- <term><literal>-v0</literal></term>
+ <term><option>-v0</option></term>
<listitem>
<para>Disable all non-essential messages (this is the
default).</para>
</varlistentry>
<varlistentry>
- <term><literal>-v1</literal></term>
+ <term><option>-v1</option></term>
<listitem>
<para>Minimal verbosity: print one line per
compilation (this is the default when
- <option>--make</option> or
- <option>--interactive</option> is on).</para>
+ <option>––make</option> or
+ <option>––interactive</option> is on).</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><literal>-v2</literal></term>
+ <term><option>-v2</option></term>
<listitem>
<para>Print the name of each compilation phase as it
is executed. (equivalent to
</varlistentry>
<varlistentry>
- <term><literal>-v3</literal></term>
+ <term><option>-v3</option></term>
<listitem>
<para>The same as <option>-v2</option>, except that in
addition the full command line (if appropriate) for
</varlistentry>
<varlistentry>
- <term><literal>-v4</literal></term>
+ <term><option>-v4</option></term>
<listitem>
<para>The same as <option>-v3</option> except that the
intermediate program representation after each
</varlistentry>
<varlistentry>
- <term><literal>--version</literal></term>
- <indexterm><primary><literal>--version</literal></primary></indexterm>
+ <term><option>-V</option></term>
+ <term><option>––version</option></term>
+ <indexterm><primary><option>-V</option></primary></indexterm>
+ <indexterm><primary><option>––version</option></primary></indexterm>
<listitem>
<para>Print a one-line string including GHC's version number.</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><literal>--numeric-version</literal></term>
- <indexterm><primary><literal>--numeric-version</literal></primary></indexterm>
+ <term><option>––numeric-version</option></term>
+ <indexterm><primary><option>––numeric-version</option></primary></indexterm>
<listitem>
<para>Print GHC's numeric version number only.</para>
</listitem>
</varlistentry>
- </variablelist>
- </sect1>
-
- <Sect1 id="options-order">
- <title>Running the right phases in the right order</title>
-
- <indexterm><primary>order of passes in GHC</primary></indexterm>
- <indexterm><primary>pass ordering in GHC</primary></indexterm>
-
-
- <para>The basic task of the <command>ghc</command> driver is to
- run each input file through the right phases (compiling, linking,
- etc.).</para>
-
- <para>The first phase to run is determined by the input-file
- suffix, and the last phase is determined by a flag. If no
- relevant flag is present, then go all the way through linking.
- This table summarises:</para>
-
-<InformalTable>
-<TGroup Cols="4">
-<ColSpec Align="Left">
-<ColSpec Align="Left">
-<ColSpec Align="Left">
-<ColSpec Align="Left">
-<TBody>
-
-<Row>
-<Entry>Phase of the compilation system</Entry>
-<Entry>Suffix saying “start here”</Entry>
-<Entry>Flag saying “stop after”</Entry>
-<Entry>(suffix of) output file</Entry>
-</Row>
-
-<Row>
-<Entry>
-literate pre-processor </Entry>
-<Entry> .lhs </Entry>
-<Entry> - </Entry>
-<Entry> .hs </Entry>
-</Row>
-<Row>
-<Entry>
-C pre-processor (opt.) </Entry>
-<Entry> .hs (with <literal>-cpp</literal>) </Entry>
-<Entry> -E </Entry>
-<Entry> .hspp </Entry>
-</Row>
-<Row>
-<Entry>
-Haskell compiler </Entry>
-<Entry> .hs </Entry>
-<Entry> -C, -S </Entry>
-<Entry> .hc, .s </Entry>
-</Row>
-<Row>
-<Entry>
-C compiler (opt.) </Entry>
-<Entry> .hc or .c </Entry>
-<Entry> -S </Entry>
-<Entry> .s </Entry>
-</Row>
-<Row>
-<Entry>
-assembler </Entry>
-<Entry> .s </Entry>
-<Entry> -c </Entry>
-<Entry> .o </Entry>
-</Row>
-<Row>
-<Entry>
-linker </Entry>
-<Entry> other </Entry>
-<Entry> - </Entry>
-<Entry> a.out </Entry>
-</Row>
-</TBody>
-</TGroup>
-</InformalTable>
-
-<IndexTerm><Primary>-C option</Primary></IndexTerm>
-<IndexTerm><Primary>-S option</Primary></IndexTerm>
-<IndexTerm><Primary>-c option</Primary></IndexTerm>
-
-<para>
-Thus, a common invocation would be: <command>ghc -c Foo.hs</command>
-</para>
-
-<para>
-Note: What the Haskell compiler proper produces depends on whether a
-native-code generator is used (producing assembly language) or not
-(producing C).
-</para>
-
- <para>NOTE: the option <option>-E</option><IndexTerm><Primary>-E
- option</Primary></IndexTerm> runs just the pre-processing passes
- of the compiler, dumping the result in a file. Note that this
- differs from all GHCs prior to version 4.11, in which the result
- was dumped to the standard output. If used in conjunction with
- -cpp, the output is the code blocks of the original (literal)
- source after having put it through the grinder that is the C
- pre-processor. Sans <option>-cpp</option>, the output is the
- de-litted version of the original source.</para>
-
- <para>The following options also affect which phases get run:</para>
-
- <variablelist>
- <varlistentry>
- <term><option>-cpp</option></term>
- <indexterm><primary><option>-cpp</option></primary></indexterm>
- <listitem>
- <para>Run the C pre-processor on the Haskell source before
- compiling it. See <xref linkend="c-pre-processor"> for more
- details.</para>
- </listitem>
- </varlistentry>
<varlistentry>
- <term><option>-fasm</option></term>
- <indexterm><primary><option>-fasm</option></primary></indexterm>
+ <term><option>––print-libdir</option></term>
+ <indexterm><primary><option>––print-libdir</option></primary></indexterm>
<listitem>
- <para>Use GHC's native code generator rather than compiling
- via C. This will compile faster (up to twice as fast), but
- may produce code that is slightly slower than compiling via
- C. <option>-fasm</option> is the default when optimisation
- is off (see <xref linkend="options-optimise">).</para>
+ <para>Print the path to GHC's library directory. This is
+ the top of the directory tree containing GHC's libraries,
+ interfaces, and include files (usually something like
+ <literal>/usr/local/lib/ghc-5.04</literal> on Unix). This
+ is the value of
+ <literal>$libdir</literal><indexterm><primary><literal>libdir</literal></primary>
+ </indexterm>in the package configuration file (see <xref
+ linkend="packages">).</para>
</listitem>
</varlistentry>
- <varlistentry>
- <term><option>-fvia-C</option></term>
- <indexterm><primary><option>-fvia-C</option></primary>
- </indexterm>
- <listitem>
- <para>Compile via C instead of using the native code
- generator. This is default for optimised compilations, and
- on architectures for which GHC doesn't have a native code
- generator.</para>
- </listitem>
- </varlistentry>
</variablelist>
</sect1>
- <sect1 id="options-output">
- <title>Re-directing the compilation output(s)</title>
-
- <indexterm><primary>output-directing options</primary></indexterm>
- <indexterm><primary>redirecting compilation output</primary></indexterm>
+ <sect1 id="make-mode">
+ <title>Using <command>ghc</command> <option>––make</option></title>
-
- <variablelist>
- <varlistentry>
- <term><literal>-o</literal></term>
- <indexterm><primary><literal>-o</literal></primary></indexterm>
- <listitem>
- <para>GHC's compiled output normally goes into a
- <filename>.hc</filename>, <filename>.o</filename>, etc.,
- file, depending on the last-run compilation phase. The
- option <option>-o foo</option><IndexTerm><Primary>-o
- option</Primary></IndexTerm> re-directs the output of that
- last-run phase to file <filename>foo</filename>.</para>
-
- <para>Note: this “feature” can be
- counterintuitive: <command>ghc -C -o foo.o foo.hs</command>
- will put the intermediate C code in the file
- <filename>foo.o</filename>, name notwithstanding!</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>-odir</literal></term>
- <indexterm><primary><literal>-odir</literal></primary></indexterm>
- <listitem>
- <para>The <option>-o</option> option isn't of much use if
- you have <emphasis>several</emphasis> input files…
- Non-interface output files are normally put in the same
- directory as their corresponding input file came from. You
- may specify that they be put in another directory using the
- <option>-odir <dir></option><IndexTerm><Primary>-odir
- <dir> option</Primary></IndexTerm> (the “Oh,
- dear” option). For example:</para>
-
-<Screen>
-% ghc -c parse/Foo.hs parse/Bar.hs gurgle/Bumble.hs -odir `arch`
-</Screen>
-
- <para>The output files, <filename>Foo.o</filename>,
- <filename>Bar.o</filename>, and
- <filename>Bumble.o</filename> would be put into a
- subdirectory named after the architecture of the executing
- machine (<filename>sun4</filename>,
- <filename>mips</filename>, etc). The directory must already
- exist; it won't be created.</para>
-
- <para>Note that the <option>-odir</option> option does
- <emphasis>not</emphasis> affect where the interface files
- are put. In the above example, they would still be put in
- <filename>parse/Foo.hi</filename>,
- <filename>parse/Bar.hi</filename>, and
- <filename>gurgle/Bumble.hi</filename>.</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>-ohi</literal></term>
- <indexterm><primary><literal>-ohi</literal></primary></indexterm>
- <listitem>
- <para></para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>-osuf</literal></term>
- <term><literal>-hisuf</literal></term>
- <indexterm><primary><literal>-osuf</literal></primary></indexterm>
- <indexterm><primary><literal>-hisuf</literal></primary></indexterm>
- <listitem>
- <para>EXOTICA: The <option>-osuf
- <suffix></option><IndexTerm><Primary>-osuf
- <suffix> option</Primary></IndexTerm> will change the
- <filename>.o</filename> file suffix for object files to
- whatever you specify. (We use this in compiling the
- prelude.).</para>
-
- <para>Similarly, the <option>-hisuf
- <suffix></option><IndexTerm><Primary>-hisuf
- <suffix> option</Primary></IndexTerm> will change the
- <filename>.hi</filename> file suffix for non-system
- interface files (see <XRef LinkEnd="hi-options">).</para>
-
- <para>The <option>-hisuf</option>/<option>-osuf</option>
- game is useful if you want to compile a program with both
- GHC and HBC (say) in the same directory. Let HBC use the
- standard <filename>.hi</filename>/<filename>.o</filename>
- suffixes; add <option>-hisuf g_hi -osuf
- g_o</option> to your <command>make</command> rule for
- GHC compiling…</para>
- </listitem>
- </varlistentry>
- </variablelist>
-
- <sect2 id="keeping-intermediates">
- <title>Keeping Intermediate Files</title>
- <indexterm><primary>intermediate files, saving</primary>
- </indexterm>
- <indexterm><primary><literal>.hc</literal> files, saving</primary>
- </indexterm>
- <indexterm><primary><literal>.s</literal> files, saving</primary>
+ <indexterm><primary><option>––make</option></primary>
+ </indexterm>
+ <indexterm><primary>separate compilation</primary>
+ </indexterm>
+
+ <para>When given the <option>––make</option> option, GHC will
+ build a multi-module Haskell program by following dependencies
+ from a single root module (usually <literal>Main</literal>). For
+ example, if your <literal>Main</literal> module is in a file
+ called <filename>Main.hs</filename>, you could compile and link
+ the program like this:</para>
+
+<screen>
+ghc ––make Main.hs
+</screen>
+
+ <para>The command line may contain any number of source file names
+ or module names; GHC will figure out all the modules in the
+ program by following the imports from these initial modules. It
+ will then attempt to compile each module which is out of date, and
+ finally if there is a <literal>Main</literal> module, the program
+ will also be linked into an executable.</para>
+
+ <para>The main advantages to using <literal>ghc ––make</literal>
+ over traditional <literal>Makefile</literal>s are:</para>
+
+ <itemizedlist>
+ <listitem>
+ <para>GHC doesn't have to be restarted for each compilation,
+ which means it can cache information between compilations.
+ Compiling a muli-module program with <literal>ghc
+ ––make</literal> can be up to twice as fast as running
+ <literal>ghc</literal> individually on each source
+ file.</para>
+ </listitem>
+ <listitem>
+ <para>You don't have to write a
+ <literal>Makefile</literal>.</para>
+ </listitem>
+ <indexterm><primary><literal>Makefile</literal>s</primary><secondary>avoiding</secondary>
</indexterm>
+ <listitem>
+ <para>GHC re-calculates the dependencies each time it is
+ invoked, so the dependencies never get out of sync with the
+ source.</para>
+ </listitem>
+ </itemizedlist>
+
+ <para>Any of the command-line options described in the rest of
+ this chapter can be used with <option>––make</option>, but note
+ that any options you give on the command line will apply to all
+ the source files compiled, so if you want any options to apply to
+ a single source file only, you'll need to use an
+ <literal>OPTIONS</literal> pragma (see <xref
+ linkend="source-file-options">).</para>
+
+ <para>If the program needs to be linked with additional objects
+ (say, some auxilliary C code), then the object files can be
+ given on the command line and GHC will include them when linking
+ the executable.</para>
+
+ <para>Note that GHC can only follow dependencies if it has the
+ source file available, so if your program includes a module for
+ which there is no source file, even if you have an object and an
+ interface file for the module, then GHC will complain. The
+ exception to this rule is for package modules, which may or may
+ not have source files.</para>
+
+ <para>The source files for the program don't all need to be in the
+ same directory; the <option>-i</option> option can be used to add
+ directories to the search path (see <xref
+ linkend="search-path">).</para>
+ </sect1>
+
+ <Sect1 id="options-order">
+ <title>GHC without <option>––make</option></title>
- <para>The following options are useful for keeping certain
- intermediate files around, when normally GHC would throw these
- away after compilation:</para>
-
- <variablelist>
- <varlistentry>
- <term><literal>-keep-hc-files</literal></term>
- <indexterm>
- <primary><literal>-keep-hc-files</literal></primary>
- </indexterm>
- <listitem>
- <para>Keep intermediate <literal>.hc</literal> files when
- doing <literal>.hs</literal>-to-<literal>.o</literal>
- compilations via C (NOTE: <literal>.hc</literal> files
- aren't generated when using the native code generator, you
- may need to use <literal>-fvia-C</literal> to force them
- to be produced).</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>-keep-s-files</literal></term>
- <indexterm>
- <primary><literal>-keep-s-files</literal></primary>
- </indexterm>
- <listitem>
- <para>Keep intermediate <literal>.s</literal> files.</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>-keep-raw-s-files</literal></term>
- <indexterm>
- <primary><literal>-keep-raw-s-files</literal></primary>
- </indexterm>
- <listitem>
- <para>Keep intermediate <literal>.raw-s</literal> files.
- These are the direct output from the C compiler, before
- GHC does “assembly mangling” to produce the
- <literal>.s</literal> file. Again, these are not produced
- when using the native code generator.</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>-keep-tmp-files</literal></term>
- <indexterm>
- <primary><literal>-keep-tmp-files</literal></primary>
- </indexterm>
- <indexterm>
- <primary>temporary files</primary>
- <secondary>keeping</secondary>
- </indexterm>
- <listitem>
- <para>Instructs the GHC driver not to delete any of its
- temporary files, which it normally keeps in
- <literal>/tmp</literal> (or possibly elsewhere; see <xref
- linkend="temp-files">). Running GHC with
- <literal>-v</literal> will show you what temporary files
- were generated along the way.</para>
- </listitem>
- </varlistentry>
- </variablelist>
- </sect2>
-
- <sect2 id="temp-files">
- <title>Redirecting temporary files</title>
-
- <indexterm>
- <primary>temporary files</primary>
- <secondary>redirecting</secondary>
- </indexterm>
+ <para>Without <option>––make</option>, GHC will compile one or
+ more source files given on the command line.</para>
- <variablelist>
- <varlistentry>
- <term><literal>-tmpdir</literal></term>
- <indexterm><primary><literal>-tmpdir</literal></primary></indexterm>
- <listitem>
- <para>If you have trouble because of running out of space
- in <filename>/tmp</filename> (or wherever your
- installation thinks temporary files should go), you may
- use the <option>-tmpdir
- <dir></option><IndexTerm><Primary>-tmpdir
- <dir> option</Primary></IndexTerm> option to specify
- an alternate directory. For example, <option>-tmpdir
- .</option> says to put temporary files in the current
- working directory.</para>
-
- <para>Alternatively, use your <Constant>TMPDIR</Constant>
- environment variable.<IndexTerm><Primary>TMPDIR
- environment variable</Primary></IndexTerm> Set it to the
- name of the directory where temporary files should be put.
- GCC and other programs will honour the
- <Constant>TMPDIR</Constant> variable as well.</para>
-
- <para>Even better idea: Set the
- <Constant>DEFAULT_TMPDIR</Constant> make variable when
- building GHC, and never worry about
- <Constant>TMPDIR</Constant> again. (see the build
- documentation).</para>
- </listitem>
- </varlistentry>
- </variablelist>
- </sect2>
+ <para>The first phase to run is determined by each input-file
+ suffix, and the last phase is determined by a flag. If no
+ relevant flag is present, then go all the way through linking.
+ This table summarises:</para>
+ <informaltable>
+ <tgroup cols="4">
+ <colspec align="left">
+ <colspec align="left">
+ <colspec align="left">
+ <colspec align="left">
+
+ <thead>
+ <row>
+ <entry>Phase of the compilation system</entry>
+ <entry>Suffix saying “start here”</entry>
+ <entry>Flag saying “stop after”</entry>
+ <entry>(suffix of) output file</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>literate pre-processor</entry>
+ <entry><literal>.lhs</literal></entry>
+ <entry>-</entry>
+ <entry><literal>.hs</literal></entry>
+ </row>
+
+ <row>
+ <entry>C pre-processor (opt.)
+ </entry>
+ <entry><literal>.hs</literal> (with
+ <option>-cpp</option>)</entry>
+ <entry><option>-E</option></entry>
+ <entry><literal>.hspp</literal></entry>
+ </row>
+
+ <row>
+ <entry>Haskell compiler</entry>
+ <entry><literal>.hs</literal></entry>
+ <entry><option>-C</option>, <option>-S</option></entry>
+ <entry><literal>.hc</literal>, <literal>.s</literal></entry>
+ </row>
+
+ <row>
+ <entry>C compiler (opt.)</entry>
+ <entry><literal>.hc</literal> or <literal>.c</literal></entry>
+ <entry><option>-S</option></entry>
+ <entry><literal>.s</literal></entry>
+ </row>
+
+ <row>
+ <entry>assembler</entry>
+ <entry><literal>.s</literal></entry>
+ <entry><option>-c</option></entry>
+ <entry><literal>.o</literal></entry>
+ </row>
+
+ <row>
+ <entry>linker</entry>
+ <entry><replaceable>other</replaceable></entry>
+ <entry>-</entry>
+ <entry><filename>a.out</filename></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+
+ <indexterm><primary><option>-C</option></primary></indexterm>
+ <indexterm><primary><option>-E</option></primary></indexterm>
+ <indexterm><primary><option>-S</option></primary></indexterm>
+ <indexterm><primary><option>-c</option></primary></indexterm>
+
+ <para>Thus, a common invocation would be: <literal>ghc -c
+ Foo.hs</literal></para>
+
+ <para>Note: What the Haskell compiler proper produces depends on
+ whether a native-code generator<indexterm><primary>native-code
+ generator</primary></indexterm> is used (producing assembly
+ language) or not (producing C). See <xref
+ linkend="options-codegen"> for more details.</para>
+
+ <para>Note: C pre-processing is optional, the
+ <option>-ccp</option><indexterm><primary><option>-cpp</option></primary>
+ </indexterm>flag turns it on. See <xref
+ linkend="c-pre-processor"> for more details.</para>
+
+ <para>Note: The option <option>-E</option><IndexTerm><Primary>-E
+ option</Primary></IndexTerm> runs just the pre-processing passes
+ of the compiler, dumping the result in a file. Note that this
+ differs from the previous behaviour of dumping the file to
+ standard output.</para>
</sect1>
+ &separate;
+
<sect1 id="options-sanity">
<title>Warnings and sanity-checking</title>
generated during compilation. By default, you get a standard set
of warnings which are generally likely to indicate bugs in your
program. These are:
- <option>-fwarn-overlpapping-patterns</option>,
+ <option>-fwarn-overlapping-patterns</option>,
<option>-fwarn-deprecations</option>,
<option>-fwarn-duplicate-exports</option>,
<option>-fwarn-missing-fields</option>, and
<para>Provides the standard warnings plus
<option>-fwarn-incomplete-patterns</option>,
<option>-fwarn-unused-matches</option>,
- <option>-fwarn-unused-imports</option> and
+ <option>-fwarn-unused-imports</option>,
+ <option>-fwarn-misc</option>, and
<option>-fwarn-unused-binds</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-w</option>:</term>
<listitem>
- <IndexTerm><Primary>-w option</Primary></IndexTerm>
+ <IndexTerm><Primary><option>-w</option></Primary></IndexTerm>
<para>Turns off all warnings, including the standard ones.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-Wall</option>:</term>
<listitem>
- <indexterm><primary>-Wall option</primary></indexterm>
+ <indexterm><primary><option>-Wall</option></primary></indexterm>
<para>Turns on all warning options.</para>
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><option>-Werror</option>:</term>
+ <listitem>
+ <indexterm><primary><option>-Werror</option></primary></indexterm>
+ <para>Makes any warning into a fatal error. Useful so that you don't
+ miss warnings when doing batch compilation. </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
<para>The full set of warning options is described below. To turn
<varlistentry>
<term><option>-fwarn-duplicate-exports</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-duplicate-exports option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-duplicate-exports</option></primary></indexterm>
<indexterm><primary>duplicate exports, warning</primary></indexterm>
<indexterm><primary>export lists, duplicates</primary></indexterm>
<varlistentry>
<term><option>-fwarn-hi-shadowing</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-hi-shadowing option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-hi-shadowing</option></primary></indexterm>
<indexterm><primary>shadowing</primary>
<secondary>interface files</secondary></indexterm>
<varlistentry>
<term><option>-fwarn-incomplete-patterns</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-incomplete-patterns option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-incomplete-patterns</option></primary></indexterm>
<indexterm><primary>incomplete patterns, warning</primary></indexterm>
<indexterm><primary>patterns, incomplete</primary></indexterm>
</varlistentry>
<varlistentry>
+ <term><option>-fwarn-misc</option>:</term>
+ <indexterm><primary><option>-fwarn-misc</option></primary></indexterm>
+ <listitem>
+ <para>Turns on warnings for various harmless but untidy
+ things. This currently includes: importing a type with
+ <literal>(..)</literal> when the export is abstract, and
+ listing duplicate class assertions in a qualified type.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><option>-fwarn-missing-fields</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-missing-fields option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-missing-fields</option></primary></indexterm>
<indexterm><primary>missing fields, warning</primary></indexterm>
<indexterm><primary>fields, missing</primary></indexterm>
<varlistentry>
<term><option>-fwarn-missing-methods</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-missing-methods option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-missing-methods</option></primary></indexterm>
<indexterm><primary>missing methods, warning</primary></indexterm>
<indexterm><primary>methods, missing</primary></indexterm>
an instance declaration is missing one or more methods, and
the corresponding class declaration has no default
declaration for them.</para>
+ <para>The warning is suppressed if the method name
+ begins with an underscore. Here's an example where this is useful:
+ <programlisting>
+ class C a where
+ _simpleFn :: a -> String
+ complexFn :: a -> a -> String
+ complexFn x y = ... _simpleFn ...
+ </programlisting>
+ The idea is that: (a) users of the class will only call <literal>complexFn</literal>;
+ never <literal>_simpleFn</literal>; and (b)
+ instance declarations can define either <literal>complexFn</literal> or <literal>_simpleFn</literal>.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-fwarn-missing-signatures</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-missing-signatures option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-missing-signatures</option></primary></indexterm>
<indexterm><primary>type signatures, missing</primary></indexterm>
<para>If you would like GHC to check that every top-level
<varlistentry>
<term><option>-fwarn-name-shadowing</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-name-shadowing option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-name-shadowing</option></primary></indexterm>
<indexterm><primary>shadowing, warning</primary></indexterm>
<para>This option causes a warning to be emitted whenever an
<varlistentry>
<term><option>-fwarn-overlapping-patterns</option>:</term>
- <indexterm><primary>-fwarn-overlapping-patterns option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-overlapping-patterns</option></primary></indexterm>
<indexterm><primary>overlapping patterns, warning</primary></indexterm>
<indexterm><primary>patterns, overlapping</primary></indexterm>
<listitem>
patterns that can fail, eg. <literal>\(x:xs)->...</literal>.
Normally, these aren't treated as incomplete patterns by
<option>-fwarn-incomplete-patterns</option>.</para>
+ <para>``Lambda-bound patterns'' includes all places where there is a single pattern,
+ including list comprehensions and do-notation. In these cases, a pattern-match
+ failure is quite legitimate, and triggers filtering (list comprehensions) or
+ the monad <literal>fail</literal> operation (monads). For example:
+ <programlisting>
+ f :: [Maybe a] -> [a]
+ f xs = [y | Just y <- xs]
+ </programlisting>
+ Switching on <option>-fwarn-simple-patterns</option> will elicit warnings about
+ these probably-innocent cases, which is why the flag is off by default. </para>
+ <para> The <literal>deriving( Read )</literal> mechanism produces monadic code with
+ pattern matches, so you will also get misleading warnings about the compiler-generated
+ code. (This is arguably a Bad Thing, but it's awkward to fix.)</para>
+
</listitem>
</varlistentry>
<varlistentry>
<term><option>-fwarn-type-defaults</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-type-defaults option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-type-defaults</option></primary></indexterm>
<indexterm><primary>defaulting mechanism, warning</primary></indexterm>
<para>Have the compiler warn/inform you where in your source
the Haskell defaulting mechanism for numeric types kicks
<varlistentry>
<term><option>-fwarn-unused-binds</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-unused-binds option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-unused-binds</option></primary></indexterm>
<indexterm><primary>unused binds, warning</primary></indexterm>
<indexterm><primary>binds, unused</primary></indexterm>
<para>Report any function definitions (and local bindings)
<varlistentry>
<term><option>-fwarn-unused-imports</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-unused-imports option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-unused-imports</option></primary></indexterm>
<indexterm><primary>unused imports, warning</primary></indexterm>
<indexterm><primary>imports, unused</primary></indexterm>
<varlistentry>
<term><option>-fwarn-unused-matches</option>:</term>
<listitem>
- <indexterm><primary>-fwarn-unused-matches option</primary></indexterm>
+ <indexterm><primary><option>-fwarn-unused-matches</option></primary></indexterm>
<indexterm><primary>unused matches, warning</primary></indexterm>
<indexterm><primary>matches, unused</primary></indexterm>
<para>Report all unused variables which arise from pattern
matches, including patterns consisting of a single variable.
For instance <literal>f x y = []</literal> would report
- <VarName>x</VarName> and <VarName>y</VarName> as unused. To
- eliminate the warning, all unused variables can be replaced
- with wildcards.</para>
+ <VarName>x</VarName> and <VarName>y</VarName> as unused. The
+ warning is suppressed if the variable name begins with an underscore, thus:
+ <programlisting>
+ f _x = True
+ </programlisting>
+ </para>
</listitem>
</varlistentry>
</VariableList>
<para>If you're feeling really paranoid, the
- <option>-dcore-lint</option> option<indexterm><primary>-dcore-lint
- option</primary></indexterm> is a good choice. It turns on
- heavyweight intra-pass sanity-checking within GHC. (It checks
- GHC's sanity, not yours.)</para>
+ <option>-dcore-lint</option>
+ option<indexterm><primary><option>-dcore-lint</option></primary></indexterm>
+ is a good choice. It turns on heavyweight intra-pass
+ sanity-checking within GHC. (It checks GHC's sanity, not
+ yours.)</para>
</sect1>
- &separate;
&packages;
<sect1 id="options-optimise">
</varlistentry>
<varlistentry>
- <term><option>-O2-for-C</option>:</term>
- <indexterm><primary>-O2-for-C option</primary></indexterm>
- <indexterm><primary>gcc, invoking with -O2</primary></indexterm>
- <listitem>
- <para>Says to run GCC with <option>-O2</option>, which may
- be worth a few percent in execution speed. Don't forget
- <option>-fvia-C</option>, lest you use the native-code
- generator and bypass GCC altogether!</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
<term><option>-Ofile <file></option>:</term>
<indexterm><primary>-Ofile <file> option</primary></indexterm>
<indexterm><primary>optimising, customised</primary></indexterm>
<para>We don't use a <option>-O*</option> flag for day-to-day
work. We use <option>-O</option> to get respectable speed;
e.g., when we want to measure something. When we want to go for
- broke, we tend to use <option>-O -fvia-C -O2-for-C</option> (and
- we go for lots of coffee breaks).</para>
+ broke, we tend to use <option>-O -fvia-C</option> (and we go for
+ lots of coffee breaks).</para>
<para>The easiest way to see what <option>-O</option> (etc.)
“really mean” is to run with <option>-v</option>,
</varlistentry>
<varlistentry>
+ <term><option>-fignore-asserts</option>:</term>
+ <listitem>
+ <indexterm><primary><option>-fignore-asserts</option></primary></indexterm>
+ <para>Causes GHC to ignore uses of the function
+ <literal>Exception.assert</literal> in source code (in
+ other words, rewriting <literal>Exception.assert p
+ e</literal> to <literal>e</literal> (see <xref
+ linkend="sec-assertions">). This flag is turned on by
+ <option>-O</option>.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><option>-fno-strictness</option></term>
<indexterm><primary><option>-fno-strictness</option></primary>
</indexterm>
</varlistentry>
<varlistentry>
- <term><option>-funfolding-interface-threshold<n></option>:</term>
- <listitem>
- <indexterm><primary><option>-funfolding-interface-threshold</option></primary></indexterm>
- <indexterm><primary>inlining, controlling</primary></indexterm>
- <indexterm><primary>unfolding, controlling</primary></indexterm>
-
- <para>(Default: 30) By raising or lowering this number,
- you can raise or lower the amount of pragmatic junk that
- gets spewed into interface files. (An unfolding has a
- “size” that reflects the cost in terms of
- “code bloat” of expanding that unfolding in
- another module. A bigger function would be assigned a
- bigger cost.)</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
<term><option>-funfolding-creation-threshold<n></option>:</term>
<listitem>
<indexterm><primary><option>-funfolding-creation-threshold</option></primary></indexterm>
<indexterm><primary>inlining, controlling</primary></indexterm>
<indexterm><primary>unfolding, controlling</primary></indexterm>
- <para>(Default: 30) This option is similar to
- <option>-funfolding-interface-threshold</option>, except
- that it governs unfoldings within a single module.
- Increasing this figure is more likely to result in longer
+ <para>(Default: 45) Governs the maximum size that GHC will
+ allow a function unfolding to be. (An unfolding has a
+ “size” that reflects the cost in terms of
+ “code bloat” of expanding that unfolding at
+ at a call site. A bigger function would be assigned a
+ bigger cost.) </para>
+
+ <para> Consequences: (a) nothing larger than this will be
+ inlined (unless it has an INLINE pragma); (b) nothing
+ larger than this will be spewed into an interface
+ file. </para>
+
+
+ <para> Increasing this figure is more likely to result in longer
compile times than faster code. The next option is more
useful:</para>
</listitem>
</variablelist>
</sect2>
-
+
</sect1>
-
-&phases;
-
-<Sect1 id="sec-using-concurrent">
+
+ &phases;
+
+ <sect1 id="sec-using-concurrent">
<title>Using Concurrent Haskell</title>
-<para>
-<indexterm><primary>Concurrent Haskell—use</primary></indexterm>
-</para>
+ <indexterm><primary>Concurrent Haskell—use</primary></indexterm>
<para>
-GHC (as of version 4.00) supports Concurrent Haskell by default,
-without requiring a special option or libraries compiled in a certain
-way. To get access to the support libraries for Concurrent Haskell
-(i.e. <literal>Concurrent</literal> and friends), use the
-<option>-package concurrent</option> option.
-</para>
+GHC supports Concurrent Haskell by default, without requiring a
+special option or libraries compiled in a certain way. To get access
+to the support libraries for Concurrent Haskell, just import
+<literal>Control.Concurrent</literal> (details are in the accompanying
+library documentation).</para>
<para>
-Three RTS options are provided for modifying the behaviour of the
-threaded runtime system. See the descriptions of
-<option>-C[<us>]</option>, <option>-q</option>, and
-<option>-t<num></option> in <XRef LinkEnd="parallel-rts-opts">.
+RTS options are provided for modifying the behaviour of the threaded
+runtime system. See <XRef LinkEnd="parallel-rts-opts">.
</para>
<para>
-Concurrent Haskell is described in more detail in <XRef
-LinkEnd="sec-Concurrent">.
+Concurrent Haskell is described in more detail in the documentation
+for the <literal>Control.Concurrent</literal> module.
</para>
</Sect1>
<para>
[You won't be able to execute parallel Haskell programs unless PVM3
-(Parallel Virtual Machine, version 3) is installed at your site.]
-</para>
+(Parallel Virtual Machine, version 3) is installed at your site.]
+</Para>
<para>
To compile a Haskell program for parallel execution under PVM, use the
-<option>-parallel</option> option,<indexterm><primary>-parallel
-option</primary></indexterm> both when compiling <emphasis>and
-linking</emphasis>. You will probably want to <literal>import
-Parallel</literal> into your Haskell modules.
-</para>
+<Option>-parallel</Option> option,<IndexTerm><Primary>-parallel
+option</Primary></IndexTerm> both when compiling <Emphasis>and
+linking</Emphasis>. You will probably want to <Literal>import
+Parallel</Literal> into your Haskell modules.
+</Para>
<para>
To run your parallel program, once PVM is going, just invoke it
“as normal”. The main extra RTS option is
-<option>-N<n></option>, to say how many PVM
+<Option>-qp<n></Option>, to say how many PVM
“processors” your program to run on. (For more details of
all relevant RTS options, please see <XRef
LinkEnd="parallel-rts-opts">.)
PVM, detailed in the following sections.
</para>
-<sect2>
-<title>Dummy's guide to using PVM</title>
+<Sect2 id="pvm-dummies">
+<Title>Dummy's guide to using PVM</Title>
<para>
<indexterm><primary>PVM, how to use</primary></indexterm>
<para>
Creating and/or controlling your “parallel machine” is a purely-PVM
-business; nothing specific to Parallel Haskell.
-</para>
+business; nothing specific to Parallel Haskell. The following paragraphs
+describe how to configure your parallel machine interactively.
+</Para>
-<para>
-You use the <command>pvm</command><indexterm><primary>pvm command</primary></indexterm> command to start PVM on your
+<Para>
+If you use parallel Haskell regularly on the same machine configuration it
+is a good idea to maintain a file with all machine names and to make the
+environment variable PVM_HOST_FILE point to this file. Then you can avoid
+the interactive operations described below by just saying
+</Para>
+
+<ProgramListing>
+pvm $PVM_HOST_FILE
+</ProgramListing>
+
+<Para>
+You use the <Command>pvm</Command><IndexTerm><Primary>pvm command</Primary></IndexTerm> command to start PVM on your
machine. You can then do various things to control/monitor your
“parallel machine;” the most useful being:
</para>
<ColSpec Align="Left">
<TBody>
-<Row>
-<Entry><KeyCombo><KeyCap>Control</KeyCap><KeyCap>D</KeyCap></KeyCombo></Entry>
-<Entry>exit <command>pvm</command>, leaving it running</Entry>
-</Row>
-
-<Row>
-<Entry><command>halt</command></Entry>
-<Entry>kill off this “parallel machine” & exit</Entry>
-</Row>
-
-<Row>
-<Entry><command>add <host></command></Entry>
-<Entry>add <command><host></command> as a processor</Entry>
-</Row>
-
-<Row>
-<Entry><command>delete <host></command></Entry>
-<Entry>delete <command><host></command></Entry>
-</Row>
-
-<Row>
-<Entry><command>reset</command></Entry>
-<Entry>kill what's going, but leave PVM up</Entry>
-</Row>
-
-<Row>
-<Entry><command>conf</command></Entry>
-<Entry>list the current configuration</Entry>
-</Row>
-
-<Row>
-<Entry><command>ps</command></Entry>
-<Entry>report processes' status</Entry>
-</Row>
-
-<Row>
-<Entry><command>pstat <pid></command></Entry>
-<Entry>status of a particular process</Entry>
-</Row>
+<row>
+<entry><KeyCombo><KeyCap>Control</KeyCap><KeyCap>D</KeyCap></KeyCombo></entry>
+<entry>exit <command>pvm</command>, leaving it running</entry>
+</row>
+
+<row>
+<entry><command>halt</command></entry>
+<entry>kill off this “parallel machine” & exit</entry>
+</row>
+
+<row>
+<entry><command>add <host></command></entry>
+<entry>add <command><host></command> as a processor</entry>
+</row>
+
+<row>
+<entry><command>delete <host></command></entry>
+<entry>delete <command><host></command></entry>
+</row>
+
+<row>
+<entry><command>reset</command></entry>
+<entry>kill what's going, but leave PVM up</entry>
+</row>
+
+<row>
+<entry><command>conf</command></entry>
+<entry>list the current configuration</entry>
+</row>
+
+<row>
+<entry><command>ps</command></entry>
+<entry>report processes' status</entry>
+</row>
+
+<row>
+<entry><command>pstat <pid></command></entry>
+<entry>status of a particular process</entry>
+</row>
</TBody>
</TGroup>
</sect2>
-<sect2>
-<title>Parallelism profiles</title>
+<Sect2 id="par-profiles">
+<Title>Parallelism profiles</Title>
<para>
<indexterm><primary>parallelism profiles</primary></indexterm>
results—only with “how parallel” it was! We want pretty pictures.
</para>
-<para>
-Parallelism profiles (à la <command>hbcpp</command>) can be generated with the
-<option>-q</option><indexterm><primary>-q RTS option (concurrent, parallel)</primary></indexterm> RTS option. The
+<Para>
+Parallelism profiles (à la <Command>hbcpp</Command>) can be generated with the
+<Option>-qP</Option><IndexTerm><Primary>-qP RTS option (concurrent, parallel)</Primary></IndexTerm> RTS option. The
per-processor profiling info is dumped into files named
-<filename><full-path><program>.gr</filename>. These are then munged into a PostScript picture,
+<Filename><full-path><program>.gr</Filename>. These are then munged into a PostScript picture,
which you can then display. For example, to run your program
-<filename>a.out</filename> on 8 processors, then view the parallelism profile, do:
-</para>
+<Filename>a.out</Filename> on 8 processors, then view the parallelism profile, do:
+</Para>
-<para>
+<Para>
<Screen>
-% ./a.out +RTS -N8 -q
-% grs2gr *.???.gr > temp.gr # combine the 8 .gr files into one
-% gr2ps -O temp.gr # cvt to .ps; output in temp.ps
-% ghostview -seascape temp.ps # look at it!
+<prompt>$</prompt> ./a.out +RTS -qP -qp8
+<prompt>$</prompt> grs2gr *.???.gr > temp.gr # combine the 8 .gr files into one
+<prompt>$</prompt> gr2ps -O temp.gr # cvt to .ps; output in temp.ps
+<prompt>$</prompt> ghostview -seascape temp.ps # look at it!
</Screen>
-</para>
+</Para>
<para>
The scripts for processing the parallelism profiles are distributed
</sect2>
-<sect2>
-<title>Other useful info about running parallel programs</title>
+<Sect2>
+<Title>Other useful info about running parallel programs</Title>
-<para>
+<Para>
The “garbage-collection statistics” RTS options can be useful for
seeing what parallel programs are doing. If you do either
-<option>+RTS -Sstderr</option><indexterm><primary>-Sstderr RTS option</primary></indexterm> or <option>+RTS -sstderr</option>, then
+<Option>+RTS -Sstderr</Option><IndexTerm><Primary>-Sstderr RTS option</Primary></IndexTerm> or <Option>+RTS -sstderr</Option>, then
you'll get mutator, garbage-collection, etc., times on standard
error. The standard error of all PE's other than the `main thread'
appears in <filename>/tmp/pvml.nnn</filename>, courtesy of PVM.
<para>
<VariableList>
-<varlistentry>
-<term><option>-N<N></option>:</term>
-<listitem>
-<para>
-<indexterm><primary>-N<N> RTS option (parallel)</primary></indexterm>
-(PARALLEL ONLY) Use <literal><N></literal> PVM processors to run this program;
+<VarListEntry>
+<Term><Option>-qp<N></Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-qp<N> RTS option</Primary></IndexTerm>
+(PARALLEL ONLY) Use <Literal><N></Literal> PVM processors to run this program;
the default is 2.
</para>
</listitem>
green queue is split into green (for the currently running thread
only) and amber (for other runnable threads). We do not recommend
that you use the verbose suboption if you are planning to use the
-<command>hbcpp</command> profiling tools or if you are context switching at every heap
-check (with <option>-C</option>).
-</para>
-</listitem>
-</varlistentry>
-<varlistentry>
-<term><option>-t<num></option>:</term>
-<listitem>
-<para>
-<indexterm><primary>-t<num> RTS option</primary></indexterm>
-(PARALLEL ONLY) Limit the number of concurrent threads per processor
-to <literal><num></literal>. The default is 32. Each thread requires slightly over 1K
-<emphasis>words</emphasis> in the heap for thread state and stack objects. (For
-32-bit machines, this translates to 4K bytes, and for 64-bit machines,
-8K bytes.)
-</para>
-</listitem>
-</varlistentry>
-<varlistentry>
-<term><option>-d</option>:</term>
-<listitem>
-<para>
-<indexterm><primary>-d RTS option (parallel)</primary></indexterm>
+<Command>hbcpp</Command> profiling tools or if you are context switching at every heap
+check (with <Option>-C</Option>).
+-->
+</Para>
+</ListItem>
+</VarListEntry>
+<VarListEntry>
+<Term><Option>-qt<num></Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-qt<num> RTS option</Primary></IndexTerm>
+(PARALLEL ONLY) Limit the thread pool size, i.e. the number of concurrent
+threads per processor to <Literal><num></Literal>. The default is
+32. Each thread requires slightly over 1K <Emphasis>words</Emphasis> in
+the heap for thread state and stack objects. (For 32-bit machines, this
+translates to 4K bytes, and for 64-bit machines, 8K bytes.)
+</Para>
+</ListItem>
+</VarListEntry>
+<!-- no more -HWL
+<VarListEntry>
+<Term><Option>-d</Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-d RTS option (parallel)</Primary></IndexTerm>
(PARALLEL ONLY) Turn on debugging. It pops up one xterm (or GDB, or
-something…) per PVM processor. We use the standard <command>debugger</command>
+something…) per PVM processor. We use the standard <Command>debugger</Command>
script that comes with PVM3, but we sometimes meddle with the
-<command>debugger2</command> script. We include ours in the GHC distribution,
-in <filename>ghc/utils/pvm/</filename>.
-</para>
-</listitem>
-</varlistentry>
-<varlistentry>
-<term><option>-e<num></option>:</term>
-<listitem>
-<para>
-<indexterm><primary>-e<num> RTS option (parallel)</primary></indexterm>
-(PARALLEL ONLY) Limit the number of pending sparks per processor to
-<literal><num></literal>. The default is 100. A larger number may be appropriate if
-your program generates large amounts of parallelism initially.
-</para>
-</listitem>
-</varlistentry>
-<varlistentry>
-<term><option>-Q<num></option>:</term>
-<listitem>
-<para>
-<indexterm><primary>-Q<num> RTS option (parallel)</primary></indexterm>
+<Command>debugger2</Command> script. We include ours in the GHC distribution,
+in <Filename>ghc/utils/pvm/</Filename>.
+</Para>
+</ListItem>
+</VarListEntry>
+-->
+<VarListEntry>
+<Term><Option>-qe<num></Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-qe<num> RTS option
+(parallel)</Primary></IndexTerm> (PARALLEL ONLY) Limit the spark pool size
+i.e. the number of pending sparks per processor to
+<Literal><num></Literal>. The default is 100. A larger number may be
+appropriate if your program generates large amounts of parallelism
+initially.
+</Para>
+</ListItem>
+</VarListEntry>
+<VarListEntry>
+<Term><Option>-qQ<num></Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-qQ<num> RTS option (parallel)</Primary></IndexTerm>
(PARALLEL ONLY) Set the size of packets transmitted between processors
-to <literal><num></literal>. The default is 1024 words. A larger number may be
+to <Literal><num></Literal>. The default is 1024 words. A larger number may be
appropriate if your machine has a high communication cost relative to
computation speed.
-</para>
-</listitem>
-</varlistentry>
+</Para>
+</ListItem>
+</VarListEntry>
+<VarListEntry>
+<Term><Option>-qh<num></Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-qh<num> RTS option (parallel)</Primary></IndexTerm>
+(PARALLEL ONLY) Select a packing scheme. Set the number of non-root thunks to pack in one packet to
+<num>-1 (0 means infinity). By default GUM uses full-subgraph
+packing, i.e. the entire subgraph with the requested closure as root is
+transmitted (provided it fits into one packet). Choosing a smaller value
+reduces the amount of pre-fetching of work done in GUM. This can be
+advantageous for improving data locality but it can also worsen the balance
+of the load in the system.
+</Para>
+</ListItem>
+</VarListEntry>
+<VarListEntry>
+<Term><Option>-qg<num></Option>:</Term>
+<ListItem>
+<Para>
+<IndexTerm><Primary>-qg<num> RTS option
+(parallel)</Primary></IndexTerm> (PARALLEL ONLY) Select a globalisation
+scheme. This option affects the
+generation of global addresses when transferring data. Global addresses are
+globally unique identifiers required to maintain sharing in the distributed
+graph structure. Currently this is a binary option. With <num>=0 full globalisation is used
+(default). This means a global address is generated for every closure that
+is transmitted. With <num>=1 a thunk-only globalisation scheme is
+used, which generated global address only for thunks. The latter case may
+lose sharing of data but has a reduced overhead in packing graph structures
+and maintaining internal tables of global addresses.
+</Para>
+</ListItem>
+</VarListEntry>
</VariableList>
</para>
</varlistentry>
<varlistentry>
- <term><option>-mlong-calls</option>:</term>
- <listitem>
- <para>(HPPA machines)<indexterm><primary>-mlong-calls option
- (HPPA only)</primary></indexterm> Means to pass the
- like-named option to GCC. Required for Very Big modules,
- maybe. (Probably means you're in trouble…)</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
<term><option>-monly-[32]-regs</option>:</term>
<listitem>
<para>(iX86 machines)<indexterm><primary>-monly-N-regs
</sect1>
-&runtime
-&debug
-&flags
+&runtime;
+
+<sect1 id="ext-core">
+ <title>Generating and compiling External Core Files</title>
+
+ <indexterm><primary>intermediate code generation</primary></indexterm>
+
+ <para>GHC can dump its optimized intermediate code (said to be in “Core” format)
+ to a file as a side-effect of compilation. Core files, which are given the suffix
+ <filename>.hcr</filename>, can be read and processed by non-GHC back-end
+ tools. The Core format is formally described in <ulink url="http://www.haskell.org/ghc/docs/papers/core.ps.gz"
+ <citetitle>An External Representation for the GHC Core Language</citetitle></ulink>,
+ and sample tools (in Haskell)
+ for manipulating Core files are available in the GHC source distribution
+ directory <literal>/fptools/ghc/utils/ext-core</literal>.
+ Note that the format of <literal>.hcr</literal>
+ files is <emphasis>different</emphasis> (though similar) to the Core output format generated
+ for debugging purposes (<xref linkend="options-debugging">).</para>
+
+ <para>The Core format natively supports notes which you can add to
+ your source code using the <literal>CORE</literal> pragma (see <xref
+ linkend="pragmas">).</para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term><option>-fext-core</option></term>
+ <indexterm>
+ <primary><option>-fext-core</option></primary>
+ </indexterm>
+ <listitem>
+ <para>Generate <literal>.hcr</literal> files.</para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+<para>GHC can also read in External Core files as source; just give the <literal>.hcr</literal> file on
+the command line, instead of the <literal>.hs</literal> or <literal>.lhs</literal> Haskell source.
+A current infelicity is that you need to give teh <literal>-fglasgow-exts</literal> flag too, because
+ordinary Haskell 98, when translated to External Core, uses things like rank-2 types.</para>
+</sect1>
+
+&debug;
+&flags;
</Chapter>
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