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\chapter{Basic concepts}
The \emph{Isabelle System Manual} describes Isabelle together with
related tools and user interfaces as seen from an outside (operating
system oriented) view. See the \emph{Isabelle Reference Manual} for
all internal {\ML} level user commands, on the other hand.
\medskip The Isabelle system level environment is based on a few
general concepts:
\begin{itemize}
\item The \emph{Isabelle settings mechanism}, which provides
environment variables to all Isabelle programs (including tools and
user interfaces).
\item \emph{Isabelle proper} (\ttindex{isabelle}), which runs logic
sessions, both interactively or in batch mode. In particular,
\texttt{isabelle} abstracts over the invocation of the actual {\ML}
system to be used.
\item The \emph{Isabelle tools wrapper} (\ttindex{isatool}), which
provides a generic startup platform for Isabelle related utilities.
Thus tools automatically benefit from the settings mechanism.
Furthermore, the shell's search path is kept clean from many small
programs.
\item The \emph{Isabelle interface wrapper}
(\ttindex{Isabelle}\footnote{Note the capital \texttt{I}!}), which
provides some abstraction over the actual user interface to be used.
\end{itemize}
\medskip The beginning user would probably just run one of the
interfaces (by invoking the capital \texttt{Isabelle}), and maybe some
basic tools like \texttt{doc} (see \S\ref{sec:tool-doc}). This
assumes that the system has already been installed properly, of
course.\footnote{In case you have to do this yourself, see the
\ttindex{INSTALL} file in the top-level directory of the
distribution. The information provided there should be sufficient as
a start.}
\section{Isabelle settings} \label{sec:settings}
The Isabelle system heavily depends on the \emph{settings
mechanism}\indexbold{settings}. Basically, this is just a collection
of environment variables, e.g.\ \texttt{ISABELLE_HOME},
\texttt{ML_SYSTEM}, \texttt{ML_HOME}. These variables are \emph{not}
intended to be set directly from the shell!
Isabelle employs a somewhat more sophisticated scheme of
\emph{settings files} --- one for site-wide defaults, another for
optional user-specific modifications. With all configuration
variables in just a few places, this is considered much more
maintainable and user-friendly than ordinary shell environment
variables.
In particular, we avoid the typical situation where prospective users
of a software package are told to put this and that in their shell
startup scripts. Isabelle requires none such administrative chores of
its end-users --- the executables can be run straight away. Usually,
users would want to put the Isabelle \texttt{bin} directory into their
shell's search path, of course.
\subsection{Building the environment}
Whenever any of the Isabelle executables is run, their settings
environment is built as follows:
\begin{enumerate}
\item The special variable \settdx{ISABELLE_HOME} is determined
automatically from the location of the binary that has been run.
You should not try to set \texttt{ISABELLE_HOME} manually. Also note
that the Isabelle executables have to be run from their original
location in the distribution directory --- copying or linking them
somewhere else just won't work!
\item The file \texttt{\$ISABELLE_HOME/etc/settings} ist run as a
shell script with the auto-export option for variables enabled.
This file typically contains a rather long list of assigments
\texttt{FOO="bar"}, thus providing the site-wide default settings.
The Isabelle distribution already contains a global settings file
with sensible defaults for most variables. When installing the
system, only a few of these have to be adapted (most likely
\texttt{ML_SYSTEM} etc.).
\item The file \texttt{\$ISABELLE_HOME_USER/etc/settings} (if it
exists) is run the same way as the site default settings. The
variable \texttt{ISABELLE_HOME_USER} has already been set before ---
usually to \texttt{\~\relax/isabelle}.
Thus individual users may override the site-wide defaults. See also
file \texttt{etc/user-settings.sample} in the distribution.
Typically, user settings are a few lines only, just containing the
assigments that are really needed. One should definitely \emph{not}
start with a full copy the central
\texttt{\$ISABELLE_HOME/etc/settings}. This could cause very
annoying maintainance problems later, when the Isabelle installation
is updated or changed otherwise.
\end{enumerate}
Note that settings files are actually full GNU bash scripts. So one
may use complex shell commands, say \texttt{if} or \texttt{case}
statements to set variables depending on the system architecture or
other environment variables, for example. Such advanced features
should be added only with great care, though. In particular, external
environment references should be kept at a minimum.
\medskip A few variables are somewhat special:
\begin{itemize}
\item \settdx{ISABELLE} and \settdx{ISATOOL} are set automatically to
the absolute path names of the \texttt{isabelle} and
\texttt{isatool} executables, respectively.
\item \settdx{ISABELLE_PATH} and \settdx{ISABELLE_OUTPUT} will have
the {\ML} system identifier (as specified by \texttt{ML_SYSTEM})
automatically appended to their values.
\end{itemize}
\medskip The Isabelle settings scheme is basically quite simple, but
non-trivial. For debugging purposes, the generated environment may be
inspected with the \texttt{getenv} utility, see
\S\ref{sec:tool-getenv}.
\subsection{Common variables}
Below is a reference of common Isabelle settings variables. Note that
the list is somewhat open-ended. Third-party utilities or interfaces
may add their own selection. Variables that are special in some sense
are marked with *.
\begin{description}
\item[\settdx{ISABELLE_HOME}*] is the location of the top-level
Isabelle distribution directory. This is automatically determined
from the Isabelle executable that has been invoked. Do not try to
set \texttt{ISABELLE_HOME} yourself from the shell.
\item[\settdx{ISABELLE_HOME_USER}] is the user-specific counterpart of
\texttt{ISABELLE_HOME}. The default value is
\texttt{\~\relax/isabelle}, under rare circumstances this may be
changed in the global setting file. Typically, the
\texttt{ISABELLE_HOME_USER} directory mimics \texttt{ISABELLE_HOME}
to some extend. In particular, site-wide defaults may be overridden
by a private \texttt{etc/settings}.
\item[\settdx{ISABELLE}*, \settdx{ISATOOL}*] are automatically set to
the full paths of the \texttt{isabelle} and \texttt{isatool}
executables, respectively. Thus other tools and scripts need not
assume that the Isabelle \texttt{bin} directory is on the current
search path of the shell.
\item[\settdx{ML_SYSTEM}, \settdx{ML_HOME}, \settdx{ML_OPTIONS}]
specify the underlying {\ML} system to be used for Isabelle. The
choice of \texttt{ML_SYSTEM} identifiers is quite fixed, see the
global \texttt{etc/settings} file for some examples. The actual
compiler binary will be run from directory \texttt{ML_HOME}, with
\texttt{ML_OPTIONS} as first arguments on the command line.
\item[\settdx{ISABELLE_PATH}*] is a list of directories (separated by
colons) where Isabelle logic images may reside. Note that the
\texttt{ML_SYSTEM} identifier is appended to each component
automatically.
\item[\settdx{ISABELLE_OUTPUT}*] is a directory where output heap
files should be stored by default. The \texttt{ML_SYSTEM} identifier
is appended here, too.
\item[\settdx{ISABELLE_LOGIC}] specifies the default logic to load if
none is given explicitely by the user --- e.g.\ when running
\texttt{isabelle} directly, or some user interface.
\item[\settdx{ISABELLE_USEDIR_OPTIONS}] is implicitely prefixed to the
command line of any \texttt{isatool usedir} invocation (see also
\S\ref{sec:tool-usedir}). This typically contains compilation
options for object-logics --- \texttt{usedir} is the basic utility
that builds them (cf.\ the \texttt{IsaMakefile}s in the
distribution).
\item[\settdx{ISABELLE_TOOLS}] is a colon separated list of
directories that are scanned by \texttt{isatool} for utility
programs (see also \S\ref{sec:isatool}).
\item[\settdx{ISABELLE_DOCS}] is a colon separated list of directories
with documentation files.
\item[\settdx{DVI_VIEWER}] specifies the command to be used for
displaying \texttt{dvi} files.
\item[\settdx{ISABELLE_INSTALL_FONTS}] determines the way that the
Isabelle symbol fonts are installed into your currently running X11
display server. X11 fonts are a non-trivial issue, see
\S\ref{sec:tool-installfonts} for more information.
\item[\settdx{ISABELLE_INTERFACE}] is an identifier that specifies the
actual user interface that the capital \texttt{Isabelle} should
invoke. Currently available are \texttt{none}, \texttt{xterm} and
\texttt{emacs}. See \S\ref{sec:interface} for more details.
\end{description}
\section{Isabelle proper --- \texttt{isabelle}}
The \ttindex{isabelle} executable runs logic sessions --- either
interactively or in batch mode. It provides an abstraction over the
underlying {\ML} system, and over the actual heap file locations. Its
usage is:
\begin{ttbox}
Usage: isabelle [OPTIONS] [INPUT] [OUTPUT]
Options are:
-e MLTEXT pass MLTEXT to the ML session
-m MODE add print mode for output
-q non-interactive session
-r open heap file read-only
INPUT (default "\$ISABELLE_LOGIC") and OUTPUT specify in/out heaps.
These are either names to be searched in the Isabelle path, or actual
file names (then containing at least one /).
If INPUT is "RAW_ML_SYSTEM", just start the bare bones ML system.
\end{ttbox}
Input files without path specifications are looked up in the
\texttt{ISABELLE_PATH} setting, which may consist of multiple
components separated by colons --- these are tried in order. Short
output names are relative to the directory specified by
\texttt{ISABELLE_OUTPUT} setting. In any case, actual file locations
may also be given by including at least one \texttt{/} in the name
(hint: use \texttt{./} to refer to the current directory).
\subsection*{Options}
If the input heap file does not have write permission bits set, or the
\texttt{-r} option is given explicitely, then the session will be
read-only. That is, the {\ML} world cannot be committed back into the
logic image. Otherwise, a writable session enables commits into
either the input file, or into an alternative output heap file (in
case this is given as the second argument).
The read-write state of sessions is determined at startup only, it
cannot be changed intermediately. Also note that heap images may
require considerable amounts of disk space. Users are responsible
themselves to dispose their heap files when they are no longer needed.
\medskip Using the \texttt{-e} option, arbitrary {\ML} code may be
passed to the Isabelle session from the command line. Multiple
\texttt{-e}'s are evaluated in order. Strange things may happen when
errorneous {\ML} code is given. Also make sure that commands are
terminated properly by semicolon.
\medskip The \texttt{-m} option adds identifiers of print modes to be
made active for this session. Typically, this is used by some user
interface, for example to enable output of mathematical symbols from a
special screen font. See also \S\ref{sec:tool-installfonts} about
fonts and the \emph{Isabelle Reference Manual} about print modes in
general.
\medskip Isabelle normally enters an interactice {\ML} top-level loop
(after processing the \texttt{-e} texts). The \texttt{-q} option
inhibits this, thus providing a pure batch mode facility.
\subsection*{Examples}
Run an interactive session of the default object-logic (as specified
by the \texttt{ISABELLE_LOGIC} setting) like this:
\begin{ttbox}
isabelle
\end{ttbox}
Usually \texttt{ISABELLE_LOGIC} refers to one of the standard logic
images, which are read-only by default. A writable session --- based
on \texttt{FOL}, but output to \texttt{Foo} (in the directory
specified by the \texttt{ISABELLE_OUTPUT} setting) --- may be invoked
as follows:
\begin{ttbox}
isabelle FOL Foo
\end{ttbox}
Ending this session normally (e.g.\ by typing control-D) dumps the
whole {\ML} system state into \texttt{Foo}. Be prepared for several
megabytes!
The \texttt{Foo} session may be continued later (still in writable
state) by:
\begin{ttbox}
isabelle Foo
\end{ttbox}
A read-only \texttt{Foo} session may be started by:
\begin{ttbox}
isabelle -r Foo
\end{ttbox}
One may also use something like \texttt{chmod~-w} on the logic image
to have them read-only automatically.
\medskip The next example demonstrates batch execution of Isabelle. We
print a certain theorem of \texttt{FOL}:
\begin{ttbox}
isabelle -e "prth allE;" -q -r FOL
\end{ttbox}
Note that the output text will be usually interspersed with some
garbage produced by the {\ML} compiler.
\section{The Isabelle tools wrapper --- \texttt{isatool}} \label{sec:isatool}
FIXME
\section{The Isabelle interface wrapper --- \texttt{Isabelle}} \label{sec:interface}
FIXME