Add :run and tweak :main

[ghc-hetmet.git] / docs / users_guide / ghci.xml

diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml
index d8d0a89..9fa5d87 100644 (file)
--- a/docs/users_guide/ghci.xml
+++ b/docs/users_guide/ghci.xml
@@ -18,7 +18,7 @@
   <indexterm><primary>FFI</primary><secondary>GHCi support</secondary></indexterm>
   <indexterm><primary>Foreign Function
   Interface</primary><secondary>GHCi support</secondary></indexterm>.
   <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>
 
   <sect1 id="ghci-introduction">
     <title>Introduction to GHCi</title>

@@ -28,64 +28,15 @@
 
 <screen>
 $ ghci
 
 <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
 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:
-
-   &lt;stmt&gt;                      evaluate/run &lt;stmt&gt;
-   :add &lt;filename&gt; ...         add module(s) to the current target set
-   :browse [*]&lt;module&gt;         display the names defined by &lt;module&gt;
-   :cd &lt;dir&gt;                   change directory to &lt;dir&gt;
-   :def &lt;cmd&gt; &lt;expr&gt;           define a command :&lt;cmd&gt;
-   :edit &lt;file&gt;                edit file
-   :edit                       edit last module
-   :help, :?                   display this list of commands
-   :info [&lt;name&gt; ...]          display information about the given names
-   :load &lt;filename&gt; ...        load module(s) and their dependents
-   :module [+/-] [*]&lt;mod&gt; ...  set the context for expression evaluation
-   :main [&lt;arguments&gt; ...]     run the main function with the given arguments
-   :reload                     reload the current module set
-
-   :set &lt;option&gt; ...           set options
-   :set args &lt;arg&gt; ...         set the arguments returned by System.getArgs
-   :set prog &lt;progname&gt;        set the value returned by System.getProgName
-   :set prompt &lt;prompt&gt;        set the prompt used in GHCi
-   :set editor &lt;cmd&gt;        set the command used for :edit
-
-   :show modules               show the currently loaded modules
-   :show bindings              show the current bindings made at the prompt
-
-   :ctags [&lt;file&gt;]             create tags file for Vi (default: "tags")
-   :etags [&lt;file&gt;]             create tags file for Emacs (default: "TAGS")
-   :type &lt;expr&gt;                show the type of &lt;expr&gt;
-   :kind &lt;type&gt;                show the kind of &lt;type&gt;
-   :undef &lt;cmd&gt;                undefine user-defined command :&lt;cmd&gt;
-   :unset &lt;option&gt; ...         unset options
-   :quit                       exit GHCi
-   :!&lt;command&gt;                 run the shell command &lt;command&gt;
-
- 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
-    -&lt;flags&gt;      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
 
     <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

@@ -268,19 +219,17 @@ Ok, modules loaded: Main.
 <screen>
 Prelude> :! ghc -c D.hs
 Prelude> :load A
 <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 B                ( B.hs, interpreted )

+Compiling C                ( C.hs, interpreted )

 Compiling A                ( A.hs, interpreted )
 Ok, modules loaded: A, B, C, D.
 *Main>
 </screen>
 
 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 
     is unchanged since the last compilation.</para>
 
     <para>At any time you can use the command 

@@ -296,7 +245,7 @@ B                ( B.hs, interpreted )
 A                ( A.hs, interpreted )
 *Main></screen>
 
 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>
     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>

@@ -305,9 +254,6 @@ A                ( A.hs, interpreted )
 *Main> :! touch D.hs
 *Main> :reload
 Compiling D                ( D.hs, interpreted )
 *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>
 Ok, modules loaded: A, B, C, D.
 *Main> 
 </screen>

@@ -323,8 +269,8 @@ Ok, modules loaded: A, B, C, D.
 *Main> :! ghc -c C.hs
 *Main> :load A
 Compiling D                ( D.hs, interpreted )
 *Main> :! ghc -c C.hs
 *Main> :load A
 Compiling D                ( D.hs, interpreted )

-Compiling C                ( C.hs, interpreted )

 Compiling B                ( B.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>
 Compiling A                ( A.hs, interpreted )
 Ok, modules loaded: A, B, C, D.
 </screen>

@@ -347,8 +293,6 @@ Ok, modules loaded: A, B, C, D.
 
 <screen>
 *Main> :load A
 
 <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.
 Compiling B                ( B.hs, interpreted )
 Compiling A                ( A.hs, interpreted )
 Ok, modules loaded: A, B, C, D.

@@ -359,7 +303,7 @@ Ok, modules loaded: A, B, C, D.
     when working on a large program is to occasionally run
     <literal>ghc &ndash;&ndash;make</literal> to compile the whole project (say
     before you go for lunch :-), then continue working in the
     when working on a large program is to occasionally run
     <literal>ghc &ndash;&ndash;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>
 
     interpreted, but the rest of the project will remain
     compiled.</para>
 

@@ -424,7 +368,6 @@ hello
       <literal>IO</literal> monad.
 <screen>
 Prelude> x &lt;- return 42
       <literal>IO</literal> monad.
 <screen>
 Prelude> x &lt;- return 42

-42

 Prelude> print x
 42
 Prelude>
 Prelude> print x
 42
 Prelude>

@@ -436,7 +379,8 @@ Prelude>
       <literal>x</literal> in future statements, for example to print
       it as we did above.</para>
 
       <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: 
+      <para>If <option>-fprint-bind-result</option> is set then
+      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 
        <itemizedlist>
          <listitem>
            <para>The statement is not a binding, or it is a monadic binding 

@@ -449,13 +393,8 @@ Prelude>
              <literal>Show</literal></para>
          </listitem>
        </itemizedlist>
              <literal>Show</literal></para>
          </listitem>
        </itemizedlist>

-      The automatic printing of binding results can be supressed with
-      <option>:set -fno-print-bind-result</option> (this does not
-      supress printing the result of non-binding statements).
-      <indexterm><primary><option>-fno-print-bind-result</option></primary></indexterm><indexterm><primary><option>-fprint-bind-result</option></primary></indexterm>.
-      You might want to do this to prevent the result of binding
-      statements from being fully evaluated by the act of printing
-      them, for example.</para>
+      <indexterm><primary><option>-fprint-bind-result</option></primary></indexterm><indexterm><primary><option>-fno-print-bind-result</option></primary></indexterm>.
+      </para>

 
       <para>Of course, you can also bind normal non-IO expressions
       using the <literal>let</literal>-statement:</para>
 
       <para>Of course, you can also bind normal non-IO expressions
       using the <literal>let</literal>-statement:</para>

@@ -480,6 +419,45 @@ Prelude>
       <para>Note that <literal>let</literal> bindings do not automatically
        print the value bound, unlike monadic bindings.</para>
 
       <para>Note that <literal>let</literal> bindings do not automatically
        print the value bound, unlike monadic bindings.</para>
 

+      <para>Hint: you can also use <literal>let</literal>-statements
+      to define functions at the prompt:</para>
+<screen>
+Prelude> let add a b = a + b
+Prelude> add 1 2
+3
+Prelude>
+</screen>
+        <para>However, this quickly gets tedious when defining functions 
+        with multiple clauses, or groups of mutually recursive functions,
+        because the complete definition has to be given on a single line, 
+        using explicit braces and semicolons instead of layout:</para>
+<screen>
+Prelude> let { f op n [] = n ; f op n (h:t) = h `op` f op n t }
+Prelude> f (+) 0 [1..3]
+6
+Prelude>
+</screen>
+      <para>To alleviate this issue, GHCi commands can be split over
+      multiple lines, by wrapping them in <literal>:{</literal> and
+      <literal>:}</literal> (each on a single line of its own):</para>
+<screen>
+Prelude> :{
+Prelude| let { g op n [] = n
+Prelude|     ; g op n (h:t) = h `op` g op n t
+Prelude|     }
+Prelude| :}
+Prelude> g (*) 1 [1..3]
+6
+</screen>
+      <para>Such multiline commands can be used with any GHCi command,
+      and the lines between <literal>:{</literal> and
+      <literal>:}</literal> are simply merged into a single line for 
+      interpretation. That implies that each such group must form a single
+      valid command when merged, and that no layout rule is used. 
+      The main purpose of multiline commands is not to replace module
+      loading but to make definitions in .ghci-files (see <xref
+      linkend="ghci-dot-files"/>) more readable and maintainable.</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
       <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

@@ -577,7 +555,9 @@ hello
 Prelude IO>
 </screen>
 
 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>
 
       <literal>:m</literal>). The full syntax of the
       <literal>:module</literal> command is:</para>
 

@@ -618,7 +598,7 @@ Prelude IO>
       <para>
         Hint: GHCi will tab-complete names that are in scope; for
         example, if you run GHCi and type <literal>J&lt;tab&gt;</literal>
       <para>
         Hint: GHCi will tab-complete names that are in scope; for
         example, if you run GHCi and type <literal>J&lt;tab&gt;</literal>

-        then GHCi will expand it to <literal>Just </literal>.
+        then GHCi will expand it to &ldquo;<literal>Just </literal>&rdquo;.

       </para>
 
       <sect3>
       </para>
 
       <sect3>

@@ -631,7 +611,7 @@ Prelude IO>
       </sect3>
 
       <sect3>
       </sect3>
 
       <sect3>

-        <title>The <literal>:main</literal> command</title>
+        <title>The <literal>:main</literal> and <literal>:run</literal> commands</title>

 
         <para>
           When a program is compiled and executed, it can use the
 
         <para>
           When a program is compiled and executed, it can use the

@@ -656,6 +636,37 @@ Prelude> :main foo bar
 ["foo","bar"]
 </screen>
 
 ["foo","bar"]
 </screen>
 

+        <para>
+            We can also quote arguments which contains characters like
+            spaces, and they are treated like Haskell strings, or we can
+            just use Haskell list syntax:
+        </para>
+
+<screen>
+Prelude> :main foo "bar baz"
+["foo","bar baz"]
+Prelude> :main ["foo", "bar baz"]
+["foo","bar baz"]
+</screen>
+
+        <para>
+            Finally, other functions can be called, either with the
+            <literal>-main-is</literal> flag or the <literal>:run</literal>
+            command:
+        </para>
+
+<screen>
+Prelude> let foo = putStrLn "foo" >> System.Environment.getArgs >>= print
+Prelude> let bar = putStrLn "bar" >> System.Environment.getArgs >>= print
+Prelude> :set -main-is foo
+Prelude> :main foo "bar baz"
+foo
+["foo","bar baz"]
+Prelude> :run bar ["foo", "bar baz"]
+bar
+["foo","bar baz"]
+</screen>
+

       </sect3>
     </sect2>
   
       </sect3>
     </sect2>
   

@@ -769,7 +780,7 @@ it &lt;- <replaceable>e</replaceable>
         </listitem>
     </orderedlist>
     At the GHCi prompt, or with GHC if the
         </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>
     the following additional differences apply:
     <itemizedlist>
         <listitem>

@@ -818,8 +829,8 @@ def = toEnum 0
     instance that returns <literal>IO a</literal>.
     However, it is only able to return
     <literal>undefined</literal>
     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>
     <literal>Integer</literal> then ghci gives an error when running a
     printf.
    </para>

@@ -842,7 +853,7 @@ def = toEnum 0
     <para>The debugger provides the following:
     <itemizedlist>
         <listitem>
     <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
             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

@@ -983,6 +994,7 @@ right :: [a]
         <literal>left</literal>:</para>
 
 <screen>
         <literal>left</literal>:</para>
 
 <screen>

+[qsort.hs:2:15-46] *Main> :set -fprint-evld-with-show

 [qsort.hs:2:15-46] *Main> :print left
 left = (_t1::[a])
 </screen>
 [qsort.hs:2:15-46] *Main> :print left
 left = (_t1::[a])
 </screen>

@@ -1002,6 +1014,13 @@ left = (_t1::[a])
         underscore, in this case
         <literal>_t1</literal>.</para>
 
         underscore, in this case
         <literal>_t1</literal>.</para>
 

+      <para>The flag <literal>-fprint-evld-with-show</literal> instructs
+      <literal>:print</literal> to reuse
+      available <literal>Show</literal> instances when possible. This happens
+      only when the contents of the variable being inspected 
+      are completely evaluated.</para>
+
+

       <para>If we aren't concerned about preserving the evaluatedness of a
         variable, we can use <literal>:force</literal> instead of
         <literal>:print</literal>.  The <literal>:force</literal> command
       <para>If we aren't concerned about preserving the evaluatedness of a
         variable, we can use <literal>:force</literal> instead of
         <literal>:print</literal>.  The <literal>:force</literal> command

@@ -1071,7 +1090,8 @@ right :: [a]
       <para>The execution continued at the point it previously stopped, and has
         now stopped at the breakpoint for a second time.</para>
 
       <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>Setting breakpoints</title>
 
         <para>Breakpoints can be set in various ways.  Perhaps the easiest way to

@@ -1134,7 +1154,7 @@ right :: [a]
         <title>Listing and deleting breakpoints</title>
 
         <para>The list of breakpoints currently enabled can be displayed using
         <title>Listing and deleting breakpoints</title>
 
         <para>The list of breakpoints currently enabled can be displayed using

-          <literal>:show&nbsp;breaks</literal></para>:
+          <literal>:show&nbsp;breaks</literal>:</para>

 <screen>
 *Main> :show breaks
 [0] Main qsort.hs:1:11-12
 <screen>
 *Main> :show breaks
 [0] Main qsort.hs:1:11-12

@@ -1160,10 +1180,14 @@ right :: [a]
 
       <para>Single-stepping is a great way to visualise the execution of your
         program, and it is also a useful tool for identifying the source of a
 
       <para>Single-stepping is a great way to visualise the execution of your
         program, and it is also a useful tool for identifying the source of a

-        bug.  The concept is simple: single-stepping enables all the
-        breakpoints in the program and executes until the next breakpoint is
-        reached, at which point you can single-step again, or continue
-        normally.  For example:</para>
+        bug. GHCi offers two variants of stepping. Use 
+       <literal>:step</literal>  to enable all the
+        breakpoints in the program, and execute until the next breakpoint is
+        reached. Use <literal>:steplocal</literal> to limit the set
+       of enabled breakpoints to those in the current top level function.
+       Similarly, use <literal>:stepmodule</literal> to single step only on
+       breakpoints contained in the current module.
+       For example:</para>

 
 <screen>
 *Main> :step main
 
 <screen>
 *Main> :step main

@@ -1172,10 +1196,11 @@ _result :: IO ()
 </screen>
 
       <para>The command <literal>:step
 </screen>
 
       <para>The command <literal>:step

-          <replaceable>expr</replaceable></literal> begins the evaluation of
+        <replaceable>expr</replaceable></literal> begins the evaluation of

         <replaceable>expr</replaceable> in single-stepping mode.  If
         <replaceable>expr</replaceable> in single-stepping mode.  If

-        <replaceable>expr</replaceable> is ommitted, then it single-steps from
-        the current breakpoint.</para>
+        <replaceable>expr</replaceable> is omitted, then it single-steps from
+        the current breakpoint. <literal>:stepover</literal> 
+        works similarly.</para>

 
       <para>The <literal>:list</literal> command is particularly useful when
         single-stepping, to see where you currently are:</para>
 
       <para>The <literal>:list</literal> command is particularly useful when
         single-stepping, to see where you currently are:</para>

@@ -1373,7 +1398,9 @@ a :: a
         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
         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
 
       <para>The GHCi debugger offers a way to hopefully shed some light on
         these errors quickly and without modifying or recompiling the source

@@ -1382,9 +1409,13 @@ a :: a
         <literal>:trace</literal> and <literal>:history</literal> to establish
         the context.  However, <literal>head</literal> is in a library and
         we can't set a breakpoint on it directly.  For this reason, GHCi
         <literal>:trace</literal> and <literal>:history</literal> to establish
         the context.  However, <literal>head</literal> is in a library and
         we can't set a breakpoint on it directly.  For this reason, GHCi

-        provides the flag <literal>-fbreak-on-exception</literal> which causes
-        the evaluator to stop when an exception is thrown, just as it does when
-        a breakpoint is hit.  This is only really useful in conjunction with
+        provides the flags <literal>-fbreak-on-exception</literal> which causes
+        the evaluator to stop when an exception is thrown, and <literal>
+       -fbreak-on-error</literal>, which works similarly but stops only on 
+       uncaught exceptions. When stopping at an exception, GHCi will act 
+       just as it does when a breakpoint is hit, with the deviation that it
+       will not show you any source code location. Due to this, these 
+       commands are only really useful in conjunction with

         <literal>:trace</literal>, in order to log the steps leading up to the
         exception.  For example:</para>
 
         <literal>:trace</literal>, in order to log the steps leading up to the
         exception.  For example:</para>
 

@@ -1437,7 +1468,7 @@ as = 'b' : 'c' : (_t1::[Char])
 <programlisting>
 import Prelude hiding (map)
 
 <programlisting>
 import Prelude hiding (map)
 

-map :: (a->b) -> a -> b
+map :: (a->b) -> [a] -> [b]

 map f [] = []
 map f (x:xs) = f x : map f xs
 </programlisting>
 map f [] = []
 map f (x:xs) = f x : map f xs
 </programlisting>

@@ -1540,7 +1571,7 @@ Just 20
         </listitem>
        <listitem><para>
          Implicit parameters (see <xref linkend="implicit-parameters"/>) are only available 
         </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>
         </listitem>
       </itemizedlist>

@@ -1568,9 +1599,7 @@ $ ghci Main.hs
 
     <para>Most of the command-line options accepted by GHC (see <xref
     linkend="using-ghc"/>) also make sense in interactive mode.  The ones
 
     <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>
 
     <sect2>
       <title>Packages</title>

@@ -1586,12 +1615,7 @@ $ ghci Main.hs
 
 <screen>
 $ ghci -package readline
 
 <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> 
 Loading package base ... linking ... done.
 Loading package readline-1.0 ... linking ... done.
 Prelude> 

@@ -1721,22 +1745,58 @@ $ ghci -lm
 
       <varlistentry>
        <term>
 
       <varlistentry>
        <term>

-          <literal>:browse</literal> <optional><literal>*</literal></optional><replaceable>module</replaceable> ...
+          <literal>:browse</literal><optional><literal>!</literal></optional> <optional><optional><literal>*</literal></optional><replaceable>module</replaceable></optional> ...

           <indexterm><primary><literal>:browse</literal></primary></indexterm>
         </term>
        <listitem>
          <para>Displays the identifiers defined by the module
          <replaceable>module</replaceable>, which must be either
           <indexterm><primary><literal>:browse</literal></primary></indexterm>
         </term>
        <listitem>
          <para>Displays the identifiers defined by the module
          <replaceable>module</replaceable>, which must be either

-         loaded into GHCi or be a member of a package.  If the
-         <literal>*</literal> symbol is placed before the module
-         name, then <emphasis>all</emphasis> the identifiers defined
-         in <replaceable>module</replaceable> are shown; otherwise
-         the list is limited to the exports of
+         loaded into GHCi or be a member of a package.  If
+         <replaceable>module</replaceable> is omitted, the most
+         recently-loaded module is used.</para>
+
+          <para>If the <literal>*</literal> symbol is placed before
+         the module name, then <emphasis>all</emphasis> the
+         identifiers in scope in <replaceable>module</replaceable> are
+         shown; otherwise the list is limited to the exports of

          <replaceable>module</replaceable>.  The
          <literal>*</literal>-form is only available for modules
          which are interpreted; for compiled modules (including
          modules from packages) only the non-<literal>*</literal>
          <replaceable>module</replaceable>.  The
          <literal>*</literal>-form is only available for modules
          which are interpreted; for compiled modules (including
          modules from packages) only the non-<literal>*</literal>

-         form of <literal>:browse</literal> is available.</para>
+    form of <literal>:browse</literal> is available.
+    If the <literal>!</literal> symbol is appended to the
+    command, data constructors and class methods will be 
+    listed individually, otherwise, they will only be listed
+    in the context of their data type or class declaration. 
+    The <literal>!</literal>-form also annotates the listing 
+    with comments giving possible imports for each group of 
+    entries.</para>
+<screen>
+Prelude> :browse! Data.Maybe
+-- not currently imported
+Data.Maybe.catMaybes :: [Maybe a] -> [a]
+Data.Maybe.fromJust :: Maybe a -> a
+Data.Maybe.fromMaybe :: a -> Maybe a -> a
+Data.Maybe.isJust :: Maybe a -> Bool
+Data.Maybe.isNothing :: Maybe a -> Bool
+Data.Maybe.listToMaybe :: [a] -> Maybe a
+Data.Maybe.mapMaybe :: (a -> Maybe b) -> [a] -> [b]
+Data.Maybe.maybeToList :: Maybe a -> [a]
+-- imported via Prelude
+Just :: a -> Maybe a
+data Maybe a = Nothing | Just a
+Nothing :: Maybe a
+maybe :: b -> (a -> b) -> Maybe a -> b
+</screen>
+  <para>
+    This output shows that, in the context of the current session, in the scope
+    of <literal>Prelude</literal>, the first group of items from
+    <literal>Data.Maybe</literal> have not been imported (but are available in
+    fully qualified form in the GHCi session - see <xref
+      linkend="ghci-scope"/>), whereas the second group of items have been
+    imported via <literal>Prelude</literal> and are therefore available either
+    unqualified, or with a <literal>Prelude.</literal> qualifier.
+  </para>

        </listitem>
       </varlistentry>
 
        </listitem>
       </varlistentry>
 

@@ -1763,16 +1823,6 @@ $ ghci -lm
 
       <varlistentry>
        <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>:cmd</literal> <replaceable>expr</replaceable>
           <indexterm><primary><literal>:cmd</literal></primary></indexterm>
         </term>
           <literal>:cmd</literal> <replaceable>expr</replaceable>
           <indexterm><primary><literal>:cmd</literal></primary></indexterm>
         </term>

@@ -1787,6 +1837,16 @@ $ ghci -lm
 
       <varlistentry>
        <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>:ctags</literal> <optional><replaceable>filename</replaceable></optional>
          <literal>:etags</literal> <optional><replaceable>filename</replaceable></optional>
          <indexterm><primary><literal>:etags</literal></primary>

@@ -1796,8 +1856,9 @@ $ ghci -lm
        </term>
        <listitem>
          <para>Generates a &ldquo;tags&rdquo; file for Vi-style editors
        </term>
        <listitem>
          <para>Generates a &ldquo;tags&rdquo; 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
+           (<literal>:ctags</literal>) or
+        Emacs-style editors (<literal>:etags</literal>).  If
+           no filename is specified, the default <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
            <filename>TAGS</filename> is
            used, respectively.  Tags for all the functions, constructors and
            types in the currently loaded modules are created.  All modules must

@@ -1808,26 +1869,27 @@ $ ghci -lm
 
       <varlistentry>
        <term>
 
       <varlistentry>
        <term>

-          <literal>:def</literal> <replaceable>name</replaceable> <replaceable>expr</replaceable>
+          <literal>:def<optional>!</optional> <optional><replaceable>name</replaceable> <replaceable>expr</replaceable></optional></literal>

           <indexterm><primary><literal>:def</literal></primary></indexterm>
         </term>
        <listitem>
           <indexterm><primary><literal>:def</literal></primary></indexterm>
         </term>
        <listitem>

-         <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><literal>:def</literal> is used to define new
+          commands, or macros, in GHCi.  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
 
          <para>That's all a little confusing, so here's a few
          examples.  To start with, here's a new GHCi command which

@@ -1871,6 +1933,12 @@ Prelude> :. cmds.ghci
           <literal>:.</literal>, by analogy with the
           &lsquo;<literal>.</literal>&rsquo; Unix shell command that
           does the same thing.</para>
           <literal>:.</literal>, by analogy with the
           &lsquo;<literal>.</literal>&rsquo; Unix shell command that
           does the same thing.</para>

+
+          <para>Typing <literal>:def</literal> on its own lists the
+          currently-defined macros.  Attempting to redefine an
+          existing command name results in an error unless the
+          <literal>:def!</literal> form is used, in which case the old
+          command with that name is silently overwritten.</para>

        </listitem>
       </varlistentry>
 
        </listitem>
       </varlistentry>
 

@@ -1904,6 +1972,15 @@ Prelude> :. cmds.ghci
 
       <varlistentry>
        <term>
 
       <varlistentry>
        <term>

+          <literal>:etags</literal> 
+        </term>
+       <listitem>
+         <para>See <literal>:ctags</literal>.</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>

           <literal>:force <replaceable>identifier</replaceable> ...</literal>
           <indexterm><primary><literal>:force</literal></primary></indexterm>
         </term>
           <literal>:force <replaceable>identifier</replaceable> ...</literal>
           <indexterm><primary><literal>:force</literal></primary></indexterm>
         </term>

@@ -1945,6 +2022,17 @@ Prelude> :. cmds.ghci
       </varlistentry>
 
       <varlistentry>
       </varlistentry>
 
       <varlistentry>

+       <term>
+          <literal>:</literal>
+          <indexterm><primary><literal>:</literal></primary></indexterm>
+        </term>
+       <listitem>
+         <para>Repeat the previous command.</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+

        <term>
           <literal>:history [<replaceable>num</replaceable>]</literal>
           <indexterm><primary><literal>:history</literal></primary></indexterm>
        <term>
           <literal>:history [<replaceable>num</replaceable>]</literal>
           <indexterm><primary><literal>:history</literal></primary></indexterm>

@@ -1972,6 +2060,12 @@ Prelude> :. cmds.ghci
          will be printed.  If <replaceable>name</replaceable> has
          been loaded from a source file, then GHCi will also display
          the location of its definition in the source.</para>
          will be printed.  If <replaceable>name</replaceable> has
          been loaded from a source file, then GHCi will also display
          the location of its definition in the source.</para>

+         <para>For types and classes, GHCi also summarises instances that
+         mention them.  To avoid showing irrelevant information, an instance
+         is shown only if (a) its head mentions <replaceable>name</replaceable>, 
+         and (b) all the other things mentioned in the instance
+         are in scope (either qualified or otherwise) as a result of 
+         a <literal>:load</literal> or <literal>:module</literal> commands. </para>

        </listitem>
       </varlistentry>
 
        </listitem>
       </varlistentry>
 

@@ -2040,7 +2134,7 @@ Prelude> :. cmds.ghci
             However, we cannot simply pass the arguments to the
             <literal>main</literal> function while we are testing in ghci,
             as the <literal>main</literal> function doesn't take its
             However, we cannot simply pass the arguments to the
             <literal>main</literal> function while we are testing in ghci,
             as the <literal>main</literal> function doesn't take its

-            directly.
+            arguments directly.

           </para>
 
           <para>
           </para>
 
           <para>

@@ -2056,6 +2150,37 @@ Prelude> :main foo bar
 ["foo","bar"]
 </screen>
 
 ["foo","bar"]
 </screen>
 

+        <para>
+            We can also quote arguments which contains characters like
+            spaces, and they are treated like Haskell strings, or we can
+            just use Haskell list syntax:
+        </para>
+
+<screen>
+Prelude> :main foo "bar baz"
+["foo","bar baz"]
+Prelude> :main ["foo", "bar baz"]
+["foo","bar baz"]
+</screen>
+
+        <para>
+            Finally, other functions can be called, either with the
+            <literal>-main-is</literal> flag or the <literal>:run</literal>
+            command:
+        </para>
+
+<screen>
+Prelude> let foo = putStrLn "foo" >> System.Environment.getArgs >>= print
+Prelude> let bar = putStrLn "bar" >> System.Environment.getArgs >>= print
+Prelude> :set -main-is foo
+Prelude> :main foo "bar baz"
+foo
+["foo","bar baz"]
+Prelude> :run bar ["foo", "bar baz"]
+bar
+["foo","bar baz"]
+</screen>
+

         </listitem>
       </varlistentry>
 
         </listitem>
       </varlistentry>
 

@@ -2064,9 +2189,15 @@ Prelude> :main foo bar
           <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>
           <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
        <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>
          more details.</para>
        </listitem>
       </varlistentry>

@@ -2079,7 +2210,7 @@ Prelude> :main foo bar
        <listitem>
          <para>Prints a value without forcing its evaluation.
             <literal>:print</literal> may be used on values whose types are
        <listitem>
          <para>Prints a value without forcing its evaluation.
             <literal>:print</literal> may be used on values whose types are

-            unkonwn or partially known, which might be the case for local
+            unknown or partially known, which might be the case for local

             variables with polymorphic types at a breakpoint.  While inspecting
             the runtime value, <literal>:print</literal> attempts to
             reconstruct the type of the value, and will elaborate the type in
             variables with polymorphic types at a breakpoint.  While inspecting
             the runtime value, <literal>:print</literal> attempts to
             reconstruct the type of the value, and will elaborate the type in

@@ -2099,7 +2230,7 @@ Prelude> :main foo bar
           <indexterm><primary><literal>:quit</literal></primary></indexterm>
         </term>
        <listitem>
           <indexterm><primary><literal>:quit</literal></primary></indexterm>
         </term>
        <listitem>

-         <para>Quits GHCi.  You can also quit by typing a control-D
+         <para>Quits GHCi.  You can also quit by typing control-D

          at the prompt.</para>
        </listitem>
       </varlistentry>
          at the prompt.</para>
        </listitem>
       </varlistentry>

@@ -2124,10 +2255,11 @@ Prelude> :main foo bar
           <indexterm><primary><literal>:set</literal></primary></indexterm>
         </term>
        <listitem>
           <indexterm><primary><literal>:set</literal></primary></indexterm>
         </term>
        <listitem>

-         <para>Sets various options.  See <xref linkend="ghci-set"/>
-         for a list of available options.  The
-         <literal>:set</literal> command by itself shows which
-         options are currently set.</para>
+    <para>Sets various options.  See <xref linkend="ghci-set"/> for a list of
+      available options and <xref linkend="interactive-mode-options"/> for a
+      list of GHCi-specific flags.  The <literal>:set</literal> command by
+      itself shows which options are currently set. It also lists the current
+      dynamic flag settings, with GHCi-specific flags listed separately.</para>

        </listitem>
       </varlistentry>
 
        </listitem>
       </varlistentry>
 

@@ -2244,10 +2376,32 @@ Prelude> :main foo bar
           <indexterm><primary><literal>:show modules</literal></primary></indexterm>
         </term>
        <listitem>
           <indexterm><primary><literal>:show modules</literal></primary></indexterm>
         </term>
        <listitem>

-         <para>Show the list of modules currently load.</para>
+         <para>Show the list of modules currently loaded.</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+          <literal>:show packages</literal>
+          <indexterm><primary><literal>:show packages</literal></primary></indexterm>
+        </term>
+       <listitem>
+    <para>Show the currently active package flags, as well as the list of
+      packages currently loaded.</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+          <literal>:show languages</literal>
+          <indexterm><primary><literal>:show languages</literal></primary></indexterm>
+        </term>
+       <listitem>
+    <para>Show the currently active language flags.</para>

        </listitem>
       </varlistentry>
 
        </listitem>
       </varlistentry>
 

+

       <varlistentry>
        <term>
           <literal>:show [args|prog|prompt|editor|stop]</literal>
       <varlistentry>
        <term>
           <literal>:show [args|prog|prompt|editor|stop]</literal>

@@ -2355,7 +2509,7 @@ Prelude> :main foo bar
 
     <para>The <literal>:set</literal> command sets two types of
     options: GHCi options, which begin with
 
     <para>The <literal>:set</literal> command sets two types of
     options: GHCi options, which begin with

-    &lsquo;<literal>+</literal>&rdquo; and &ldquo;command-line&rdquo;
+    &lsquo;<literal>+</literal>&rsquo;, and &ldquo;command-line&rdquo;

     options, which begin with &lsquo;-&rsquo;.  </para>
 
     <para>NOTE: at the moment, the <literal>:set</literal> command
     options, which begin with &lsquo;-&rsquo;.  </para>
 
     <para>NOTE: at the moment, the <literal>:set</literal> command

@@ -2467,9 +2621,10 @@ Prelude> :set -fno-glasgow-exts
     <indexterm><primary>startup</primary><secondary>files, GHCi</secondary>
     </indexterm>
 
     <indexterm><primary>startup</primary><secondary>files, GHCi</secondary>
     </indexterm>
 

-    <para>When it starts, GHCi always reads and executes commands from
-    <filename>$HOME/.ghci</filename>, followed by
-    <filename>./.ghci</filename>.</para>
+    <para>When it starts, unless the <literal>-ignore-dot-ghci</literal>
+    flag is given, GHCi reads and executes commands from
+    <filename>./.ghci</filename>, followed by
+    <filename>$HOME/.ghci</filename>.</para>

 
     <para>The <filename>.ghci</filename> in your home directory is
     most useful for turning on favourite options (eg. <literal>:set
 
     <para>The <filename>.ghci</filename> in your home directory is
     most useful for turning on favourite options (eg. <literal>:set

@@ -2478,7 +2633,7 @@ Prelude> :set -fno-glasgow-exts
     project is a useful way to set certain project-wide options so you
     don't have to type them everytime you start GHCi: eg. if your
     project uses GHC extensions and CPP, and has source files in three
     project is a useful way to set certain project-wide options so you
     don't have to type them everytime you start GHCi: eg. if your
     project uses GHC extensions and CPP, and has source files in three

-    subdirectories A B and C, you might put the following lines in
+    subdirectories A, B and C, you might put the following lines in

     <filename>.ghci</filename>:</para>
 
 <screen>
     <filename>.ghci</filename>:</para>
 
 <screen>

@@ -2626,7 +2781,19 @@ Prelude> :set -fno-glasgow-exts
        <term>I can't use Control-C to interrupt computations in
           GHCi on Windows.</term>
         <listitem>
        <term>I can't use Control-C to interrupt computations in
           GHCi on Windows.</term>
         <listitem>

-          <para>See <xref linkend="ghci-windows"/></para>
+          <para>See <xref linkend="ghci-windows"/>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>The default buffering mode is different in GHCi to GHC.</term>
+        <listitem>
+          <para>
+            In GHC, the stdout handle is line-buffered by default.
+            However, in GHCi we turn off the buffering on stdout,
+            because this is normally what you want in an interpreter:
+            output appears as it is generated.
+          </para>

         </listitem>
       </varlistentry>
     </variablelist>
         </listitem>
       </varlistentry>
     </variablelist>