[project @ 2001-03-23 15:25:30 by simonmar]

document :def and :undef

diff --git a/ghc/docs/users_guide/ghci.sgml b/ghc/docs/users_guide/ghci.sgml
index 35694a5..8e4836e 100644 (file)
--- a/ghc/docs/users_guide/ghci.sgml
+++ b/ghc/docs/users_guide/ghci.sgml
@@ -628,10 +628,55 @@ $ ghci -lm
       </varlistentry>
 
       <varlistentry>
-       <term><literal>:def</literal></term>
+       <term><literal>:def</literal> <replaceable>name</replaceable> <replaceable>expr</replaceable></term>
        <indexterm><primary><literal>:def</literal></primary></indexterm>
        <listitem>
-         <para>ToDo.</para>
+         <para>The command <literal>:def</literal>
+         <replaceable>name</replaceable>
+         <replaceable>expr</replaceable> defines a new GHCi command
+         <literal>:<replaceable>name</replaceable></literal>,
+         implemented by the Haskell expression
+         <replaceable>expr</replaceable>, which must have type
+         <literal>String -> IO String</literal>.  When
+         <literal>:<replaceable>name</replaceable>
+         <replaceable>args</replaceable></literal> is typed at the
+         prompt, GHCi will run the expression
+         <literal>(<replaceable>name</replaceable>
+         <replaceable>args</replaceable>)</literal>, take the
+         resulting <literal>String</literal>, and feed it back into
+         GHCi as a new sequence of commands.  Separate commands in
+         the result must be separated by
+         &lsquo;<literal>\n</literal>&rsquo;.</para>
+
+         <para>That's all a little confusing, so here's a few
+         examples.  To start with, here's a new GHCi command which
+         doesn't take any arguments or produce any results, it just
+         outputs the current date & time:</para>
+
+<screen>
+Prelude> let date _ = Time.getClockTime >>= print >> return ""
+Prelude> :def date date
+Prelude> :date
+Fri Mar 23 15:16:40 GMT 2001
+</screen>
+
+         <para>Here's an example of a command that takes an argument.
+         It's a re-implementation of <literal>:cd</literal>:</para>
+
+<screen>
+Prelude> let mycd d = Directory.setCurrentDirectory d >> return ""
+Prelude> :def mycd mycd
+Prelude> :mycd ..
+</screen>
+
+         <para>Or I could define a simple way to invoke
+         &ldquo;<literal>ghc --make Main</literal>&rdquo; in the
+         current directory:</para>
+
+<screen>
+Prelude> :def make (\_ -> return ":! ghc --make Main")
+</screen>
+
        </listitem>
       </varlistentry>
 
@@ -715,6 +760,16 @@ $ ghci -lm
       </varlistentry>
 
       <varlistentry>
+       <term><literal>:undef</literal> <replaceable>name</replaceable></term>
+       <indexterm><primary><literal>:undef</literal></primary></indexterm>
+       <listitem>
+         <para>Undefines the user-defined command
+         <replaceable>name</replaceable> (see <literal>:def</literal>
+         above).</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
        <term><literal>:unset</literal> <replaceable>option</replaceable>...</term>
        <indexterm><primary><literal>:unset</literal></primary></indexterm>
        <listitem>