: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
+
: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 (defauilt: "TAGS")
:type <expr> show the type of <expr>
:kind <type> show the kind of <type>
:undef <cmd> undefine user-defined command :<cmd>
<literal>x</literal> in future statements, for example to print
it as we did above.</para>
+ <para>GHCi will print the result of a statement if and only if:
+ <itemizedlist>
+ <listitem>
+ <para>The statement is not a binding, or it is a monadic binding
+ (<literal>p <- e</literal>) that binds exactly one
+ variable.</para>
+ </listitem>
+ <listitem>
+ <para>The variable's type is not polymorphic, is not
+ <literal>()</literal>, and is an instance of
+ <literal>Show</literal></para>
+ </listitem>
+ </itemizedlist>
+ </para>
+
<para>Of course, you can also bind normal non-IO expressions
using the <literal>let</literal>-statement:</para>
<screen>
Prelude> let x = 42
-42
-Prelude> print x
+Prelude> x
42
Prelude>
</screen>
- <para>An important difference between the two types of binding
+ <para>Another important difference between the two types of binding
is that the monadic bind (<literal>p <- e</literal>) is
<emphasis>strict</emphasis> (it evaluates <literal>e</literal>),
whereas with the <literal>let</literal> form, the expression
*** Exception: help!
Prelude>
</screen>
-<para>GHCi will print the result of a
-<literal>x<-e</literal> statement if and only if:
-<itemizedlist>
-<listitem><para>The statement binds exactly one variable</para></listitem>
-<listitem><para>The variable's type is not polymorphic, is not
-<literal>()</literal>,
-and is an instance of <literal>Show</literal>
-</para></listitem>
-</itemizedlist>
+
+ <para>Note that <literal>let</literal> bindings do not automatically
+ print the value bound, unlike monadic bindings.</para>
+
<para>Any exceptions raised during the evaluation or execution
of the statement are caught and printed by the GHCi command line
interface (for more information on exceptions, see the module
<literal>Control.Exception</literal> in the libraries
documentation).</para>
-
<para>Every new binding shadows any existing bindings of the
same name, including entities that are in scope in the current
module context.</para>
x :: Integer
xs :: [Integer]
</screen>
-</para>
+
</sect2>
<sect2 id="ghci-scope">
At the GHCi prompt, the second and third rules are relaxed as follows
(differences italicised):
<itemizedlist>
- <listitem><para> <emphasis>Any</emphasis> of the classes <literal>Ci</literal> is standard.</para></listitem>
+ <listitem><para> <emphasis>All</emphasis> of the classes
+ <literal>Ci</literal> are single-parameter type classes.</para></listitem>
<listitem><para> At least one of the classes <literal>Ci</literal> is
numeric, <emphasis>or is <literal>Show</literal>,
<literal>Eq</literal>, or <literal>Ord</literal></emphasis>.</para></listitem>
<varlistentry>
<term>
<literal>:set</literal> <literal>args</literal> <replaceable>arg</replaceable> ...
- <indexterm><primary><literal>:set</literal></primary></indexterm>
+ <indexterm><primary><literal>:set args</literal></primary></indexterm>
</term>
<listitem>
<para>Sets the list of arguments which are returned when the
<varlistentry>
<term>
<literal>:set</literal> <literal>prog</literal> <replaceable>prog</replaceable>
- <indexterm><primary><literal>:set</literal></primary></indexterm>
+ <indexterm><primary><literal>:set prog</literal></primary></indexterm>
</term>
<listitem>
<para>Sets the string to be returned when the program calls
<varlistentry>
<term>
+ <literal>:set</literal> <literal>prompt</literal> <replaceable>prompt</replaceable>
+ </term>
+ <listitem>
+ <para>Sets the string to be used as the prompt in GHCi.
+ Inside <replaceable>prompt</replaceable>, the sequence
+ <literal>%s</literal> is replaced by the names of the
+ modules currently in scope, and <literal>%%</literal> is
+ replaced by <literal>%</literal>.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
<literal>:show bindings</literal>
<indexterm><primary><literal>:show bindings</literal></primary></indexterm>
</term>
<varlistentry>
<term>
+ <literal>:ctags</literal> <optional><replaceable>filename</replaceable></optional>
+ <literal>:etags</literal> <optional><replaceable>filename</replaceable></optional>
+ <indexterm><primary><literal>:etags</literal></primary>
+ </indexterm>
+ <indexterm><primary><literal>:etags</literal></primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>Generates a “tags” file for Vi-style editors
+ (<literal>:ctags</literal>) or Emacs-style editors (<literal>etags</literal>). If
+ no filename is specified, the defaulit <filename>tags</filename> or
+ <filename>TAGS</filename> is
+ used, respectively. Tags for all the functions, constructors and
+ types in the currently loaded modules are created. All modules must
+ be interpreted for these commands to work.</para>
+ <para>See also <xref linkend="hasktags" />.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
<literal>:type</literal> <replaceable>expression</replaceable>
<indexterm><primary><literal>:type</literal></primary></indexterm>
</term>
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