Hi,
I like David's proposal. It strikes a good balance between newbie
friendly and detailed enough foundations (you don't learn Peano's Axioms
before learning to count).
Cheers,
Offray
On 13/01/16 09:27, David Allouche wrote:
Hey,
Since I just recently figured that stuff out, my perspective might be
useful.
I do not think it is a good idea to push external VCS too much at this
point. They are important to collaboration, so they should be
mentioned, but they add a lot of complexity.
Taking into account the feedback from Sven, and my own ideas, here's
how I would write it. I hope this helps.
1. The *virtual machine* (VM) provides the environment where the
Pharo system lives. It is different for each operating system and
hardware architecture, and runs as a machine language executable
in the operating system. It implements the details of managing
memory, executing Pharo byte-code, and communicating with the
world outside of the Pharo system: files, other operating system
process, and the network.
2. The *image* is the state of all objects in a running Pharo system:
classes, method as source and byte-code, windows, VM processes.
All of those are objects. The virtual machine can load image
files, and save running images back to disk.
3. The *sources* file is a way to save space by putting the source
code of classes outside of the image. Since an image contains
byte-compiled methods, it can run without its associated sources
files. This file only provides information that useful to the
programmer. It is generated once per major release of Pharo, and
is usually stored in the same directory as the image. Several
images can use the same sources file.
4. The *changes* file logs all source code changes since the
generation of the sources file. It lets you examine and revert
source code changes. It also serves as a journal so you can
recover changes you made but did not save to the disk image, by
mistake or because of a crash. An image does not need its changes
file to run. Each change file belong to a single image.
NOTE: Some virtual machines run in web browsers, and are Javascript
programs instead of machine language. They provide the same services
as other virtual machines, they just treat Javascript as the machine
language and the browser as the operating system.
The image, sources and changes files are portable across operating
systems, and can be copied and run on any appropriate virtual machine.
The format of the sources and changes file is defined by code stored
in the image, not the VM.
A complete Pharo release contains the following files:
* An executable virtual machine, named:
o Pharo.exe for Windows;
o pharo for Linux;
o Pharo for OS X (inside a package named Pharo.app).
* An image, named after the release: Pharo4.0.image
* A sources file, named after the release: PharoV40.sources.
* A nearly empty changes file, named after the image: Pharo4.0.changes
They are starting point for a live environment that you adapt to your
needs. The .image file containes the byte-compiler of the language,
the language parser, the IDE tools, many libraries and provide a
virtual operating system that runs on top of a virtual machine.
As you work in Pharo, the .image and .changes files are modified, so
you need to make sure that they are writable.
The .image and .changes files are intimately linked and should always
be kept together, with matching filenames. Never edit them directly
with a text editor, as .images holds your live object runtime memory,
which indexes into the .changes files for the source.
It is a good idea to keep a backup copy of the
downloaded .image and .changes files so you can always start from a
fresh image and reload your code. But to manage changes on larger
projects you should also use a version control system that will
provide more control to record and communicate your changes.
The four main component files above can be placed in the same
directory, although it’s also possible to put the Virtual Machine and
sources file in a separate directory where everyone has read-only
access to them.
If more than one image file is present in the same directory pharo
will prompt you to choose an image file you want to load.
Do whatever works best for your style of working and your operating
system.
