@node The REPL
@chapter The REPL
@anchor{quick-start}
If you've followed the indications in @ref{Setting it up}, your Emacs is
now ready to start playing. Otherwise, i'll wait for you: when you're
ready, just come back here and proceed to the following sections.

@menu
* Starting the REPL::
* First aids::
* Switching contexts::
@end menu

@node Starting the REPL, First aids, The REPL, The REPL
@section Starting the REPL

To start a Scheme REPL (meaning, a scheme process offering you a
Read-Eval-Print Loop), Geiser provides the generic interactive command
@command{run-geiser}. If you run it (via, as is customary in Emacs,
@kbd{M-x run-geiser}, you'll be saluted by a prompt asking which one of
the supported implementations you want to launch (yes, you can stop the
asking: see below). Tabbing for completion will offer you, as of this
writing, @code{guile} and @code{racket}. Just choose your poison, and a
new REPL buffer will pop-up.

@image{img/repls}

If all went according to plan, you'll be facing an
implementation-dependent banner, followed by an interactive prompt.
Going according to plan includes having the executable of the Scheme you
chose in your path. If that's not the case, you can tell Emacs where it
is by setting the variable @var{geiser-<impl>-binary} to an appropriate
value. Returning to our REPL, the first thing to notice is that the
funny prompt is telling you your current module: its name is the part
just after the @@ sign (in Guile, that means @code{guile-user}, while
Racket's top namespace doesn't have a name; cf. @ref{Switching contexts}
below). Other than that, this is pretty much equivalent to having a
command-line interpreter in a terminal, with a bunch of add-ons that
we'll be reviewing below. You can start typing sexps right there: Geiser
will only dispatch them for evaluation when they're complete, and will
indent new lines properly until then.

@node First aids, Switching contexts, Starting the REPL, The REPL
@section First aids

@img{repl-menu, right}
A quick way of seeing what else Geiser's REPL can do for you, is to
display the corresponding entry up there in your menu bar. No, i don't
normally use menus either; but they can come in handy until you've
memorized Geiser's commands, as a learning device. And yes, i usually
run Emacs inside a terminal, but one can always use
@uref{http://www.emacswiki.org/emacs/LaCarte, La Carte} to access the
menus in a convenient enough fashion.

Or just press @kbd{C-h m} and be done with that.

Among the commands at your disposal, we find the familiar input
navigation keys, with a twist. By default, @kbd{M-p} and @kbd{M-n} are
bound to @i{matching} items in your input history. That is, they'll find
the previous or next sexp that start with the current input prefix
(defined as the text between the end of the prompt and your current
position, a.k.a. @dfn{point}, in the buffer). For going up and down the
list unconditionally, just use @kbd{C-c M-p} and @kbd{C-c M-n}.

There are also a few commands to twiddle with the Scheme process.
@kbd{C-c C-q} will mercilessly kill it (but not before stowing your
history in the file system). A softer nuke is performed by @kbd{C-c
C-k}: some (rare, i promise) times, Geiser's REPL can get confused by
the input received from then underlying Scheme (specially if you have
multiple threads writing to the standard ports), and become
irresponsive; you can try this command to try to revive it without
killing the process. Finally, if bad comes to worst and the process is
dead, @kbd{C-c z} will restart it.

The remaining commands are meatier, and deserve sections of their own.

@node Switching contexts,  , First aids, The REPL
@section Switching contexts
@comment  node-name,  next,  previous,  up


@c Local Variables:
@c mode: texinfo
@c TeX-master: "geiser"
@c End: