Multi-platform support of Isabelle

==================================

Preamble

--------

The general programming model is that of a stylized ML + Scala + POSIX

environment, with a minimum of system-specific code in user-space

tools.

The Isabelle system infrastructure provides some facilities to make

this work, e.g. see the ML and Scala modules File and Path, or

functions like Isabelle_System.bash.  The settings environment also

provides some means for portability, e.g. the bash function

"platform_path" to keep the impression that Windows/Cygwin adheres to

Isabelle/POSIX standards, although Poly/ML and the JVM are native on

Windows.

When producing add-on tools, it is important to stay within this clean

room of Isabelle, and refrain from non-portable access to operating

system functions. The Isabelle environment uses peculiar scripts for

GNU bash and perl as system glue: this style should be observed as far

as possible.

Supported platforms

-------------------

The following hardware and operating system platforms are officially

supported by the Isabelle distribution (and bundled tools), with the

following base-line versions (which have been selected to be neither

too old nor too new):

  x86_64-linux      Ubuntu 12.04 LTS

  x86_64-darwin     Mac OS X 10.10 Yosemite (macbroy31 MacBookPro6,2)

                    Mac OS X 10.11 El Capitan (macbroy2 MacPro4,1)

                    macOS 10.12 Sierra (macbroy30 MacBookPro6,2)

                    macOS 10.13 High Sierra

  x86_64-windows    Windows 7

  x86_64-cygwin     Cygwin 2.10 https://isabelle.sketis.net/cygwin_2018 (x86_64/release)

All of the above platforms are 100% supported by Isabelle -- end-users

should not have to care about the differences (at least in theory).

Exotic platforms like BSD, Solaris, NixOS are not supported.

64 bit vs. 32 bit platform personality

--------------------------------------

Isabelle requires 64 bit hardware running a 64 bit operating

system. Windows and Mac OS X allow x86 executables as well, but for

Linux this requires separate installation of 32 bit shared

libraries. The POSIX emulation on Windows via Cygwin64 works

exclusively for x86_64.

Poly/ML supports both for x86_64 and x86, and the latter is preferred

for space and performance reasons. Java is always the x86_64 version

on all platforms.

Add-on executables are expected to work without manual user

configuration. Each component settings script needs to determine the

platform details appropriately.

The Isabelle settings environment provides the following important

variables to help configuring platform-dependent tools:

  ISABELLE_PLATFORM64  (potentially empty)

  ISABELLE_PLATFORM32  (potentially empty)

Each can be empty, but not both at the same time. Using GNU bash

notation, tools may express their platform preference, e.g. first 64

bit and second 32 bit, or the opposite:

  "${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}"

  "${ISABELLE_PLATFORM32:-$ISABELLE_PLATFORM64}"

There is a another set of settings for native Windows (instead of the

POSIX emulation of Cygwin used before):

  ISABELLE_WINDOWS_PLATFORM64

  ISABELLE_WINDOWS_PLATFORM32

These are always empty on Linux and Mac OS X, and non-empty on

Windows. They can be used like this to prefer native Windows and then

Unix (first 64 bit second 32 bit):

  "${ISABELLE_WINDOWS_PLATFORM64:-${ISABELLE_WINDOWS_PLATFORM32:-${ISABELLE_PLATFORM64:-$ISABELLE_PLATFORM32}}}"

Dependable system tools

-----------------------

The following portable system tools can be taken for granted:

* Scala on top of Java.  Isabelle/Scala irons out many oddities and

  portability issues of the Java platform.

* GNU bash as uniform shell on all platforms. The POSIX "standard"

  shell /bin/sh does *not* work portably -- there are too many

  non-standard implementations of it. On Debian and Ubuntu /bin/sh is

  actually /bin/dash and introduces many oddities.

* Perl as largely portable system programming language, with its

  fairly robust support for processes, signals, sockets etc.

Known problems

--------------

* Mac OS X: If MacPorts is installed there is some danger that

  accidental references to its shared libraries are created

  (e.g. libgmp).  Use otool -L to check if compiled binaries also work

  without MacPorts.

* Mac OS X: If MacPorts is installed and its version of Perl takes

  precedence over /usr/bin/perl in the PATH, then the end-user needs

  to take care of installing extra modules, e.g. for HTTP support.

  Such add-ons are usually included in Apple's /usr/bin/perl by

  default.

* Common Unix tools like /bin/sh, /bin/kill, sed, ulimit are

  notoriously non-portable an should be avoided.

* The traditional "uname" Unix tool only tells about its own executable

  format, not the underlying platform!