doc-src/System/Thy/Basics.thy

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theory Basics
imports Pure
begin

chapter {* The Isabelle system environment *}

text {*
  This manual describes Isabelle together with related tools and user
  interfaces as seen from a system oriented view.  See also the
  \emph{Isabelle/Isar Reference Manual}~\cite{isabelle-isar-ref} for
  the actual Isabelle input language and related concepts.

  \medskip The Isabelle system environment provides the following
  basic infrastructure to integrate tools smoothly.

  \begin{enumerate}

  \item The \emph{Isabelle settings} mechanism provides process
  environment variables to all Isabelle executables (including tools
  and user interfaces).

  \item The \emph{raw Isabelle process} (@{executable_ref
  "isabelle-process"}) runs logic sessions either interactively or in
  batch mode.  In particular, this view abstracts over the invocation
  of the actual ML system to be used.  Regular users rarely need to
  care about the low-level process.

  \item The \emph{Isabelle tools wrapper} (@{executable_ref isabelle})
  provides a generic startup environment Isabelle related utilities,
  user interfaces etc.  Such tools automatically benefit from the
  settings mechanism.

  \end{enumerate}
*}


section {* Isabelle settings \label{sec:settings} *}

text {*
  The Isabelle system heavily depends on the \emph{settings
  mechanism}\indexbold{settings}.  Essentially, this is a statically
  scoped collection of environment variables, such as @{setting
  ISABELLE_HOME}, @{setting ML_SYSTEM}, @{setting ML_HOME}.  These
  variables are \emph{not} intended to be set directly from the shell,
  though.  Isabelle employs a somewhat more sophisticated scheme of
  \emph{settings files} --- one for site-wide defaults, another for
  additional user-specific modifications.  With all configuration
  variables in at most two places, this scheme is more maintainable
  and user-friendly than global shell environment variables.

  In particular, we avoid the typical situation where prospective
  users of a software package are told to put several things into
  their shell startup scripts, before being able to actually run the
  program. Isabelle requires none such administrative chores of its
  end-users --- the executables can be invoked straight away.
  Occasionally, users would still want to put the @{"file"
  "$ISABELLE_HOME/bin"} directory into their shell's search path, but
  this is not required.
*}


subsection {* Bootstrapping the environment \label{sec:boot} *}

text {* Isabelle executables need to be run within a proper settings
  environment.  This is bootstrapped as described below, on the first
  invocation of one of the outer wrapper scripts (such as
  @{executable_ref isabelle}).  This happens only once for each
  process tree, i.e.\ the environment is passed to subprocesses
  according to regular Unix conventions.

  \begin{enumerate}

  \item The special variable @{setting_def ISABELLE_HOME} is
  determined automatically from the location of the binary that has
  been run.
  
  You should not try to set @{setting ISABELLE_HOME} manually. Also
  note that the Isabelle executables either have to be run from their
  original location in the distribution directory, or via the
  executable objects created by the @{tool install} utility.  Symbolic
  links are admissible, but a plain copy of the @{"file"
  "$ISABELLE_HOME/bin"} files will not work!

  \item The file @{"file" "$ISABELLE_HOME/etc/settings"} is run as a
  @{executable_ref bash} shell script with the auto-export option for
  variables enabled.
  
  This file holds a rather long list of shell variable assigments,
  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 may have to be adapted (probably @{setting ML_SYSTEM}
  etc.).
  
  \item The file @{verbatim "$ISABELLE_HOME_USER/etc/settings"} (if it
  exists) is run in the same way as the site default settings. Note
  that the variable @{setting ISABELLE_HOME_USER} has already been set
  before --- usually to @{verbatim "~/.isabelle"}.
  
  Thus individual users may override the site-wide defaults.  See also
  file @{"file" "$ISABELLE_HOME/etc/user-settings.sample"} in the
  distribution.  Typically, a user settings file would contain only a
  few lines, just the assigments that are really changed.  One should
  definitely \emph{not} start with a full copy the basic @{"file"
  "$ISABELLE_HOME/etc/settings"}. This could cause very annoying
  maintainance problems later, when the Isabelle installation is
  updated or changed otherwise.
  
  \end{enumerate}

  Since settings files are regular GNU @{executable_def bash} scripts,
  one may use complex shell commands, such as @{verbatim "if"} or
  @{verbatim "case"} statements to set variables depending on the
  system architecture or other environment variables.  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 @{setting_def ISABELLE_PROCESS} and @{setting_def ISABELLE_TOOL} are set
  automatically to the absolute path names of the @{executable
  "isabelle-process"} and @{executable isabelle} executables,
  respectively.
  
  \item @{setting_ref ISABELLE_OUTPUT} will have the identifiers of
  the Isabelle distribution (cf.\ @{setting ISABELLE_IDENTIFIER}) and
  the ML system (cf.\ @{setting ML_IDENTIFIER}) appended automatically
  to its value.

  \end{itemize}

  \medskip Note that the settings environment may be inspected with
  the Isabelle tool @{tool getenv}.  This might help to figure out the
  effect of complex settings scripts.
*}


subsection{* Common variables *}

text {*
  This 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 @{text "\<^sup>*"}.

  \begin{description}

  \item[@{setting_def ISABELLE_HOME}@{text "\<^sup>*"}] is the
  location of the top-level Isabelle distribution directory. This is
  automatically determined from the Isabelle executable that has been
  invoked.  Do not attempt to set @{setting ISABELLE_HOME} yourself
  from the shell!
  
  \item[@{setting_def ISABELLE_HOME_USER}] is the user-specific
  counterpart of @{setting ISABELLE_HOME}. The default value is
  @{verbatim "~/.isabelle"}, under rare circumstances this may be
  changed in the global setting file.  Typically, the @{setting
  ISABELLE_HOME_USER} directory mimics @{setting ISABELLE_HOME} to
  some extend. In particular, site-wide defaults may be overridden by
  a private @{verbatim "$ISABELLE_HOME_USER/etc/settings"}.
  
  \item[@{setting_def ISABELLE_PROCESS}@{text "\<^sup>*"}, @{setting
  ISABELLE_TOOL}@{text "\<^sup>*"}] are automatically set to the full path
  names of the @{executable "isabelle-process"} and @{executable
  isabelle} executables, respectively.  Thus other tools and scripts
  need not assume that the @{"file" "$ISABELLE_HOME/bin"} directory is
  on the current search path of the shell.
  
  \item[@{setting_def ISABELLE_IDENTIFIER}@{text "\<^sup>*"}] refers
  to the name of this Isabelle distribution, e.g.\ ``@{verbatim
  Isabelle2008}''.

  \item[@{setting_def ML_SYSTEM}, @{setting_def ML_HOME},
  @{setting_def ML_OPTIONS}, @{setting_def ML_PLATFORM}, @{setting_def
  ML_IDENTIFIER}@{text "\<^sup>*"}] specify the underlying ML system
  to be used for Isabelle.  There is only a fixed set of admissable
  @{setting ML_SYSTEM} names (see the @{"file"
  "$ISABELLE_HOME/etc/settings"} file of the distribution).
  
  The actual compiler binary will be run from the directory @{setting
  ML_HOME}, with @{setting ML_OPTIONS} as first arguments on the
  command line.  The optional @{setting ML_PLATFORM} may specify the
  binary format of ML heap images, which is useful for cross-platform
  installations.  The value of @{setting ML_IDENTIFIER} is
  automatically obtained by composing the values of @{setting
  ML_SYSTEM}, @{setting ML_PLATFORM} and the Isabelle version values.
  
  \item[@{setting_def ISABELLE_PATH}] is a list of directories
  (separated by colons) where Isabelle logic images may reside.  When
  looking up heaps files, the value of @{setting ML_IDENTIFIER} is
  appended to each component internally.
  
  \item[@{setting_def ISABELLE_OUTPUT}@{text "\<^sup>*"}] is a
  directory where output heap files should be stored by default. The
  ML system and Isabelle version identifier is appended here, too.
  
  \item[@{setting_def ISABELLE_BROWSER_INFO}] is the directory where
  theory browser information (HTML text, graph data, and printable
  documents) is stored (see also \secref{sec:info}).  The default
  value is @{verbatim "$ISABELLE_HOME_USER/browser_info"}.
  
  \item[@{setting_def ISABELLE_LOGIC}] specifies the default logic to
  load if none is given explicitely by the user.  The default value is
  @{verbatim HOL}.
  
  \item[@{setting_def ISABELLE_LINE_EDITOR}] specifies the default
  line editor for the @{tool_ref tty} interface.

  \item[@{setting_def ISABELLE_USEDIR_OPTIONS}] is implicitly prefixed
  to the command line of any @{tool_ref usedir} invocation. This
  typically contains compilation options for object-logics --- @{tool
  usedir} is the basic utility for managing logic sessions (cf.\ the
  @{verbatim IsaMakefile}s in the distribution).

  \item[@{setting_def ISABELLE_FILE_IDENT}] specifies a shell command
  for producing a source file identification, based on the actual
  content instead of the full physical path and date stamp (which is
  the default). A typical identification would produce a ``digest'' of
  the text, using a cryptographic hash function like SHA-1, for
  example.
  
  \item[@{setting_def ISABELLE_LATEX}, @{setting_def
  ISABELLE_PDFLATEX}, @{setting_def ISABELLE_BIBTEX}, @{setting_def
  ISABELLE_DVIPS}] refer to {\LaTeX} related tools for Isabelle
  document preparation (see also \secref{sec:tool-latex}).
  
  \item[@{setting_def ISABELLE_TOOLS}] is a colon separated list of
  directories that are scanned by @{executable isabelle} for external
  utility programs (see also \secref{sec:isabelle-tool}).
  
  \item[@{setting_def ISABELLE_DOCS}] is a colon separated list of
  directories with documentation files.
  
  \item[@{setting_def ISABELLE_DOC_FORMAT}] specifies the preferred
  document format, typically @{verbatim dvi} or @{verbatim pdf}.
  
  \item[@{setting_def DVI_VIEWER}] specifies the command to be used
  for displaying @{verbatim dvi} files.
  
  \item[@{setting_def PDF_VIEWER}] specifies the command to be used
  for displaying @{verbatim pdf} files.
  
  \item[@{setting_def PRINT_COMMAND}] specifies the standard printer
  spool command, which is expected to accept @{verbatim ps} files.
  
  \item[@{setting_def ISABELLE_TMP_PREFIX}@{text "\<^sup>*"}] is the
  prefix from which any running @{executable "isabelle-process"}
  derives an individual directory for temporary files.  The default is
  somewhere in @{verbatim "/tmp"}.
  
  \end{description}
*}


subsection {* Additional components \label{sec:components} *}

text {* Any directory may be registered as an explicit \emph{Isabelle
  component}.  The general layout conventions are that of the main
  Isabelle distribution itself, and the following two files (both
  optional) have a special meaning:

  \begin{itemize}

  \item @{verbatim "etc/settings"} holds additional settings that are
  initialized when bootstrapping the overall Isabelle environment,
  cf.\ \secref{sec:boot}.  As usual, the content is interpreted as a
  @{verbatim bash} script.  It may refer to the component's enclosing
  directory via the @{verbatim "COMPONENT"} shell variable.

  For example, the following setting allows to refer to files within
  the component later on, without having to hardwire absolute paths:

  \begin{ttbox}
  MY_COMPONENT_HOME="$COMPONENT"
  \end{ttbox}

  Components can also add to existing Isabelle settings such as
  @{setting_def ISABELLE_TOOLS}, in order to provide
  component-specific tools that can be invoked by end-users.  For
  example:

  \begin{ttbox}
  ISABELLE_TOOLS="$ISABELLE_TOOLS:$COMPONENT/lib/Tools"
  \end{ttbox}

  \item @{verbatim "etc/components"} holds a list of further
  sub-components of the same structure.  The directory specifications
  given here can be either absolute (with leading @{verbatim "/"}) or
  relative to the component's main directory.

  \end{itemize}

  The root of component initialization is @{setting ISABELLE_HOME}
  itself.  After initializing all of its sub-components recursively,
  @{setting ISABELLE_HOME_USER} is included in the same manner (if
  that directory exists).  Thus users can easily add private
  components to @{verbatim "$ISABELLE_HOME_USER/etc/components"}.
*}


section {* The raw Isabelle process *}

text {*
  The @{executable_def "isabelle-process"} executable runs bare-bones
  Isabelle 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-process [OPTIONS] [INPUT] [OUTPUT]

  Options are:
    -I           startup Isar interaction mode
    -P           startup Proof General interaction mode
    -S           secure mode -- disallow critical operations
    -W OUTPUT    startup process wrapper, with messages going to OUTPUT stream
    -X           startup PGIP interaction mode
    -e MLTEXT    pass MLTEXT to the ML session
    -f           pass 'Session.finish();' to the ML session
    -m MODE      add print mode for output
    -q           non-interactive session
    -r           open heap file read-only
    -u           pass 'use"ROOT.ML";' to the ML session
    -w           reset write permissions on OUTPUT

  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 (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
  @{setting ISABELLE_PATH} setting, which may consist of multiple
  components separated by colons --- these are tried in the given
  order with the value of @{setting ML_IDENTIFIER} appended
  internally.  In a similar way, base names are relative to the
  directory specified by @{setting ISABELLE_OUTPUT}.  In any case,
  actual file locations may also be given by including at least one
  slash (@{verbatim "/"}) in the name (hint: use @{verbatim "./"} to
  refer to the current directory).
*}


subsubsection {* Options *}

text {*
  If the input heap file does not have write permission bits set, or
  the @{verbatim "-r"} option is given explicitely, then the session
  started will be read-only.  That is, the ML world cannot be
  committed back into the image file.  Otherwise, a writable session
  enables commits into either the input file, or into another output
  heap file (if that is given as the second argument on the command
  line).

  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 (approximately
  50--200~MB). Users are responsible for themselves to dispose their
  heap files when they are no longer needed.

  \medskip The @{verbatim "-w"} option makes the output heap file
  read-only after terminating.  Thus subsequent invocations cause the
  logic image to be read-only automatically.

  \medskip Using the @{verbatim "-e"} option, arbitrary ML code may be
  passed to the Isabelle session from the command line. Multiple
  @{verbatim "-e"}'s are evaluated in the given order. Strange things
  may happen when errorneous ML code is provided. Also make sure that
  the ML commands are terminated properly by semicolon.

  \medskip The @{verbatim "-u"} option is a shortcut for @{verbatim
  "-e"} passing ``@{verbatim "use \"ROOT.ML\";"}'' to the ML session.
  The @{verbatim "-f"} option passes ``@{verbatim
  "Session.finish();"}'', which is intended mainly for administrative
  purposes.

  \medskip The @{verbatim "-m"} option adds identifiers of print modes
  to be made active for this session. Typically, this is used by some
  user interface, e.g.\ to enable output of proper mathematical
  symbols.

  \medskip Isabelle normally enters an interactive top-level loop
  (after processing the @{verbatim "-e"} texts). The @{verbatim "-q"}
  option inhibits interaction, thus providing a pure batch mode
  facility.

  \medskip The @{verbatim "-I"} option makes Isabelle enter Isar
  interaction mode on startup, instead of the primitive ML top-level.
  The @{verbatim "-P"} option configures the top-level loop for
  interaction with the Proof General user interface, and the
  @{verbatim "-X"} option enables XML-based PGIP communication.  The
  @{verbatim "-W"} option makes Isabelle enter a special process
  wrapper for interaction via an external program; the protocol is a
  stripped-down version of Proof General the interaction mode, see
  also @{"file" "~~/src/Pure/System/isabelle_process.ML"} and @{"file"
  "~~/src/Pure/System/isabelle_process.scala"}.

  \medskip The @{verbatim "-S"} option makes the Isabelle process more
  secure by disabling some critical operations, notably runtime
  compilation and evaluation of ML source code.
*}


subsubsection {* Examples *}

text {*
  Run an interactive session of the default object-logic (as specified
  by the @{setting ISABELLE_LOGIC} setting) like this:
\begin{ttbox}
isabelle-process
\end{ttbox}

  Usually @{setting ISABELLE_LOGIC} refers to one of the standard
  logic images, which are read-only by default.  A writable session
  --- based on @{verbatim FOL}, but output to @{verbatim Foo} (in the
  directory specified by the @{setting ISABELLE_OUTPUT} setting) ---
  may be invoked as follows:
\begin{ttbox}
isabelle-process FOL Foo
\end{ttbox}
  Ending this session normally (e.g.\ by typing control-D) dumps the
  whole ML system state into @{verbatim Foo}. Be prepared for several
  tens of megabytes.

  The @{verbatim Foo} session may be continued later (still in
  writable state) by:
\begin{ttbox}
isabelle-process Foo
\end{ttbox}
  A read-only @{verbatim Foo} session may be started by:
\begin{ttbox}
isabelle-process -r Foo
\end{ttbox}

  \medskip Note that manual session management like this does
  \emph{not} provide proper setup for theory presentation.  This would
  require the @{tool usedir} utility.

  \bigskip The next example demonstrates batch execution of Isabelle.
  We retrieve the @{verbatim FOL} theory value from the theory loader
  within ML:
\begin{ttbox}
isabelle-process -e 'theory "FOL";' -q -r FOL
\end{ttbox}
  Note that the output text will be interspersed with additional junk
  messages by the ML runtime environment.  The @{verbatim "-W"} option
  allows to communicate with the Isabelle process via an external
  program in a more robust fashion.
*}


section {* The Isabelle tools wrapper \label{sec:isabelle-tool} *}

text {*
  All Isabelle related tools and interfaces are called via a common
  wrapper --- @{executable isabelle}:

\begin{ttbox}
Usage: isabelle TOOL [ARGS ...]

  Start Isabelle tool NAME with ARGS; pass "-?" for tool specific help.

  Available tools are:

    browser - Isabelle graph browser
    \dots
\end{ttbox}

  In principle, Isabelle tools are ordinary executable scripts that
  are run within the Isabelle settings environment, see
  \secref{sec:settings}.  The set of available tools is collected by
  @{executable isabelle} from the directories listed in the @{setting
  ISABELLE_TOOLS} setting.  Do not try to call the scripts directly
  from the shell.  Neither should you add the tool directories to your
  shell's search path!
*}


subsubsection {* Examples *}

text {*
  Show the list of available documentation of the current Isabelle
  installation like this:

\begin{ttbox}
  isabelle doc
\end{ttbox}

  View a certain document as follows:
\begin{ttbox}
  isabelle doc isar-ref
\end{ttbox}

  Create an Isabelle session derived from HOL (see also
  \secref{sec:tool-mkdir} and \secref{sec:tool-make}):
\begin{ttbox}
  isabelle mkdir HOL Test && isabelle make
\end{ttbox}
  Note that @{verbatim "isabelle mkdir"} is usually only invoked once;
  existing sessions (including document output etc.) are then updated
  by @{verbatim "isabelle make"} alone.
*}

end