<indexterm><primary>FFI</primary><secondary>GHCi support</secondary></indexterm>
<indexterm><primary>Foreign Function
Interface</primary><secondary>GHCi support</secondary></indexterm>.
- GHCi also includes an interactive debugger (see <xref linkend="ghci-debugger"/>)..</para>
+ GHCi also includes an interactive debugger (see <xref linkend="ghci-debugger"/>).</para>
<sect1 id="ghci-introduction">
<title>Introduction to GHCi</title>
<screen>
$ ghci
- ___ ___ _
- / _ \ /\ /\/ __(_)
- / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98.
-/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
-\____/\/ /_/\____/|_| Type :? for help.
-
+GHCi, version 6.8.1: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
Prelude>
</screen>
<para>There may be a short pause while GHCi loads the prelude and
- standard libraries, after which the prompt is shown. If we follow
- the instructions and type <literal>:?</literal> for help, we
- get:</para>
-
-<screen>
- Commands available from the prompt:
-
- <stmt> evaluate/run <stmt>
- :add <filename> ... add module(s) to the current target set
- :browse [*]<module> display the names defined by <module>
- :cd <dir> change directory to <dir>
- :def <cmd> <expr> define a command :<cmd>
- :edit <file> edit file
- :edit edit last module
- :help, :? display this list of commands
- :info [<name> ...] display information about the given names
- :load <filename> ... load module(s) and their dependents
- :module [+/-] [*]<mod> ... set the context for expression evaluation
- :main [<arguments> ...] run the main function with the given arguments
- :reload reload the current module set
-
- :set <option> ... set options
- :set args <arg> ... set the arguments returned by System.getArgs
- :set prog <progname> set the value returned by System.getProgName
- :set prompt <prompt> set the prompt used in GHCi
- :set editor <cmd> set the command used for :edit
-
- :show modules show the currently loaded modules
- :show bindings show the current bindings made at the prompt
-
- :ctags [<file>] create tags file for Vi (default: "tags")
- :etags [<file>] create tags file for Emacs (default: "TAGS")
- :type <expr> show the type of <expr>
- :kind <type> show the kind of <type>
- :undef <cmd> undefine user-defined command :<cmd>
- :unset <option> ... unset options
- :quit exit GHCi
- :!<command> run the shell command <command>
-
- Options for ':set' and ':unset':
-
- +r revert top-level expressions after each evaluation
- +s print timing/memory stats after each evaluation
- +t print type after evaluation
- -<flags> most GHC command line flags can also be set here
- (eg. -v2, -fglasgow-exts, etc.)
-</screen>
+ standard libraries, after which the prompt is shown. As the banner
+ says, you can type <literal>:?</literal> to see the list of commands
+ available, and a half line description of each of them.</para>
<para>We'll explain most of these commands as we go along. For
Hugs users: many things work the same as in Hugs, so you should be
<screen>
Prelude> :! ghc -c D.hs
Prelude> :load A
-Skipping D ( D.hs, D.o )
-Compiling C ( C.hs, interpreted )
Compiling B ( B.hs, interpreted )
+Compiling C ( C.hs, interpreted )
Compiling A ( A.hs, interpreted )
Ok, modules loaded: A, B, C, D.
*Main>
</screen>
- <para>In the messages from the compiler, we see that it skipped D,
- and used the object file <filename>D.o</filename>. The message
- <literal>Skipping</literal> <replaceable>module</replaceable>
- indicates that compilation for <replaceable>module</replaceable>
- isn't necessary, because the source and everything it depends on
+ <para>In the messages from the compiler, we see that there is no line
+ for <literal>D</literal>. This is because
+ it isn't necessary to compile <literal>D</literal>,
+ because the source and everything it depends on
is unchanged since the last compilation.</para>
<para>At any time you can use the command
A ( A.hs, interpreted )
*Main></screen>
- <para>If we now modify the source of D (or pretend to: using Unix
+ <para>If we now modify the source of D (or pretend to: using the Unix
command <literal>touch</literal> on the source file is handy for
this), the compiler will no longer be able to use the object file,
because it might be out of date:</para>
*Main> :! touch D.hs
*Main> :reload
Compiling D ( D.hs, interpreted )
-Skipping C ( C.hs, interpreted )
-Skipping B ( B.hs, interpreted )
-Skipping A ( A.hs, interpreted )
Ok, modules loaded: A, B, C, D.
*Main>
</screen>
*Main> :! ghc -c C.hs
*Main> :load A
Compiling D ( D.hs, interpreted )
-Compiling C ( C.hs, interpreted )
Compiling B ( B.hs, interpreted )
+Compiling C ( C.hs, interpreted )
Compiling A ( A.hs, interpreted )
Ok, modules loaded: A, B, C, D.
</screen>
<screen>
*Main> :load A
-Skipping D ( D.hs, D.o )
-Skipping C ( C.hs, C.o )
Compiling B ( B.hs, interpreted )
Compiling A ( A.hs, interpreted )
Ok, modules loaded: A, B, C, D.
when working on a large program is to occasionally run
<literal>ghc ––make</literal> to compile the whole project (say
before you go for lunch :-), then continue working in the
- interpreter. As you modify code, the new modules will be
+ interpreter. As you modify code, the changed modules will be
interpreted, but the rest of the project will remain
compiled.</para>
Prelude IO>
</screen>
- <para>(Note: <literal>:module</literal> can be shortened to
+ <para>(Note: you can use <literal>import M</literal> as an
+ alternative to <literal>:module +M</literal>, and
+ <literal>:module</literal> can also be shortened to
<literal>:m</literal>). The full syntax of the
<literal>:module</literal> command is:</para>
<para>
Hint: GHCi will tab-complete names that are in scope; for
example, if you run GHCi and type <literal>J<tab></literal>
- then GHCi will expand it to <literal>Just </literal>.
+ then GHCi will expand it to “<literal>Just </literal>”.
</para>
<sect3>
</listitem>
</orderedlist>
At the GHCi prompt, or with GHC if the
- <literal>-fextended-default-rules</literal> flag is given,
+ <literal>-XExtendedDefaultRules</literal> flag is given,
the following additional differences apply:
<itemizedlist>
<listitem>
instance that returns <literal>IO a</literal>.
However, it is only able to return
<literal>undefined</literal>
- (the reason for the instance having this type is to not require
- extensions to the class system), so if the type defaults to
+ (the reason for the instance having this type is so that printf
+ doesn't require extensions to the class system), so if the type defaults to
<literal>Integer</literal> then ghci gives an error when running a
printf.
</para>
<para>The debugger provides the following:
<itemizedlist>
<listitem>
- <para>The abilty to set a <firstterm>breakpoint</firstterm> on a
+ <para>The ability to set a <firstterm>breakpoint</firstterm> on a
function definition or expression in the program. When the function
is called, or the expression evaluated, GHCi suspends
execution and returns to the prompt, where you can inspect the
<para>The execution continued at the point it previously stopped, and has
now stopped at the breakpoint for a second time.</para>
- <sect3 id="setting-breakpoings">
+ <sect3 id="setting-breakpoints">
<title>Setting breakpoints</title>
<para>Breakpoints can be set in various ways. Perhaps the easiest way to
<title>Listing and deleting breakpoints</title>
<para>The list of breakpoints currently enabled can be displayed using
- <literal>:show breaks</literal></para>:
+ <literal>:show breaks</literal>:</para>
<screen>
*Main> :show breaks
[0] Main qsort.hs:1:11-12
have no context information attached to them. Finding which
particular call to <literal>head</literal> in your program resulted in
the error can be a painstaking process, usually involving
- <literal>Debug.Trace.trace</literal>.</para>
+ <literal>Debug.Trace.trace</literal>, or compiling with
+ profiling and using <literal>+RTS -xc</literal> (see <xref
+ linkend="prof-time-options" />).</para>
<para>The GHCi debugger offers a way to hopefully shed some light on
these errors quickly and without modifying or recompiling the source
</listitem>
<listitem><para>
Implicit parameters (see <xref linkend="implicit-parameters"/>) are only available
- at the scope of a breakpoint if there is a explicit type signature.
+ at the scope of a breakpoint if there is an explicit type signature.
</para>
</listitem>
</itemizedlist>
<para>Most of the command-line options accepted by GHC (see <xref
linkend="using-ghc"/>) also make sense in interactive mode. The ones
- that don't make sense are mostly obvious; for example, GHCi
- doesn't generate interface files, so options related to interface
- file generation won't have any effect.</para>
+ that don't make sense are mostly obvious.</para>
<sect2>
<title>Packages</title>
<screen>
$ ghci -package readline
- ___ ___ _
- / _ \ /\ /\/ __(_)
- / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98.
-/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
-\____/\/ /_/\____/|_| Type :? for help.
-
+GHCi, version 6.8.1: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
Loading package readline-1.0 ... linking ... done.
Prelude>
<varlistentry>
<term>
- <literal>:continue</literal>
- <indexterm><primary><literal>:continue</literal></primary></indexterm>
- </term>
- <listitem><para>Continue the current evaluation, when stopped at a
- breakpoint.</para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
<literal>:cmd</literal> <replaceable>expr</replaceable>
<indexterm><primary><literal>:cmd</literal></primary></indexterm>
</term>
<varlistentry>
<term>
+ <literal>:continue</literal>
+ <indexterm><primary><literal>:continue</literal></primary></indexterm>
+ </term>
+ <listitem><para>Continue the current evaluation, when stopped at a
+ breakpoint.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
<literal>:ctags</literal> <optional><replaceable>filename</replaceable></optional>
<literal>:etags</literal> <optional><replaceable>filename</replaceable></optional>
<indexterm><primary><literal>:etags</literal></primary>
<literal>:module <optional>+|-</optional> <optional>*</optional><replaceable>mod<subscript>1</subscript></replaceable> ... <optional>*</optional><replaceable>mod<subscript>n</subscript></replaceable></literal>
<indexterm><primary><literal>:module</literal></primary></indexterm>
</term>
+ <term>
+ <literal>import <replaceable>mod</replaceable></literal>
+ </term>
<listitem>
<para>Sets or modifies the current context for statements
- typed at the prompt. See <xref linkend="ghci-scope"/> for
+ typed at the prompt. The form <literal>import
+ <replaceable>mod</replaceable></literal> is equivalent to
+ <literal>:module +<replaceable>mod</replaceable></literal>.
+ See <xref linkend="ghci-scope"/> for
more details.</para>
</listitem>
</varlistentry>
projects / ghc-hetmet.git / blobdiff