Monthly Archives: June 2012

The Bootstrap Chronicles Chapter 4 – Pump up with Fuel

Last time we were generating a new image with useful information.  This post tells the story after that first bootstrap: How we ensure that little monster is healthy, and how we ensure that our process is flexible and robust enough, and how does it help pharo in the modularization cruzade.

Fuel – The modularization sword

Probably some of you already know about Fuel: a fast object serializer written by Mariano Peck and Martín Dias. And maybe you are also aware of another Google Summer of Code Martín is working on: a Binary Package manager on top of fuel. Mariano showed us already a first proof of concept of that idea in this post: http://marianopeck.wordpress.com/2011/09/24/importing-and-exporting-packages-with-fuel/.

So, I want to work on building stuff on top of my little bootstrapped image.  And I thought Fuel was a nice gun to attack that problem.

Detecting illnesses

In my last post about the bootstrap I’ve already shown you how to get a list of broken/uninitialized stuff. That gives us an idea of how healthy our image is.  But there are other tools that we already use for that: tests.

So, Can we run SUnit on the bootstrap? Yes.

When I thought about Fuel and the bootstrap, I thought Fuel should be included by default, otherwise it should be difficult make it grow.  Of course I could’ve chosen the compiler for the same purpose.  But I’d like to enable modularization with binary packages.

So, what about exporting sunit as a binary package, and import it in the bootstrap? And what if we also export the tests over sunit, and include them also? Then we should be able to run the tests of sunit. Nice. Then this same idea can be applied to tests the kernel, or the compiler…

And I did it :)

Completeness (or “does it have all its essential parts?”)

Another thing we can think on is testing the completeness.  When should you consider that the bootstrap is complete? A fun definition could be “when it is able to define itself”. Ok, let’s export the bootstrapping code with fuel, and import it in the bootstrapped image, and let’s try to bootstrap from the bootstrap. And do it again, just for fun.

Once the bootstrap bootstrap was working, I put the tests to work on the last generation of bootstraps.

The results

I’ve created some Jobs to test all this stuff in the Ecole de Mines’ Jenkins.

The test results are exported in JUnit format, so we can tell what’s broken and look at the stack trace.  All this jobs are working on the bleeding edge of the project using latest Pharo image and latest CogVM.

Have Fun!

Guille

Smalltalk behind the scenes: the meta model

Have you ever evaluated this pieces of code in Pharo?

 ProtoObject superclass.
 ProtoObject class superclass.
 Metaclass class class = Metaclass.

Wait, WTF? How is that ProtoObject superclass is nil? Wait again, and the one of it’s superclass is Class? Metaclass class is an instance of Metaclass? Hey, that’s kind of the chiken and the egg problem, which one was first?

You know that when you create a class, you specify a superclass for it.  This superclass will specify some other properties and the VM will use it to perform the method lookup.

Also, probably you already know that when a class is created in Smalltalk, a metaclass is created for it implicitly. That metaclass describes the class side behavior: class side methods, class instance variables…

Funny thing about this implicit metamodel, is that a second class hierarchy is built in parallel to the original class hierarchy.

Now, if you think about this, you can understand why the method lookup works also in the class side methods, and they are not static like in Java or C# :).

You can have a look at the following invariants:

aClass superclass class = aClass class superclass.
aClass class class = Metaclass.

Which of course have it’s exceptions. The method lookup ends when it reaches a class whose superclass is nil.  And the class side objects also behave like a Class, because they finally inherit from Class. HA! But then the metaclass hierarchy re-enters the non-metaclass hierarchy. Thinking of this in an operational way is kind of meta confusing, isn’t it?

But this is not the motivation of this post. The motivation is this: Are we really coupled to that meta model?  How can I create my own?

If you remember from my post on vm limitations I learned during the bootstap, the vm only expects 3 things from a class:

  • that it’s first instance variable is it’s superclass.
  • that it’s second instance variable is it’s method dictionary.
  • that it’s third instance variable is it’s format.

Any object respecting that contract can be treated like a class by the VM.  Then you can think on creating your own metaclass loop, kind of independent from the original one…

classFormat := ...
metaclassFormat := ...

"This metaclass defines how our metaclass instances will be.  It is only here to define the first metaclass format, and it will be discarded"
metaclassClass := Metaclass new.
metaclassClass
superclass: Class
methodDictionary: (MethodDictionary new)
         format: classFormat.

metaclass := metaclassClass basicNew.
metaclass instVarAt: 1 put: Metaclass.
metaclass instVarAt: 2 put: MethodDictionary new.
metaclass instVarAt: 3 put: metaclassFormat.

metaclassClass := metaclass basicNew.
metaclassClass instVarAt: 1 put: Metaclass class.
metaclassClass instVarAt: 2 put: MethodDictionary new.
metaclassClass instVarAt: 3 put: classFormat.

metaclassClass adoptInstance: metaclass.

Once you have a metaclass, instantiate it to create your class, and instanciate it to create your little object! That’s crafting Smalltalk using Smalltalk. Well, that is bootstrapping the meta model :).
The only ugly thing is that in order to create a new meta model with different instance variables, you have to create a transient class in the middle, because the VM does not like to have objects with a format X, whose class defines a format Y… So the hack just solves the format problem :).

Now you can think about simpler stuff like a class instance of itself, subclass of nil. Or more complex one :).

You can change it, I told you. Now it’s up to you how to use it…

The Bootstrap Chronicles Chapter 3 – It’s Alive!

So now that you now a bit what the bootstrap is about and what are some of the problems to face.  I’ll show you some solutions and progress for real.

How does the bootstrap implementation work

To bootstrap a Smalltalk environment, you need to create a new environment, with it’s classes and objects, and initialize some state in them. I could have done that in C, using mallocs and initializing everything by hand using plain memory :). But doing it in smalltalk is easier: you have late binding, polymorphism, closures…  Even, once you have done your first steps in the bootstrap, you can send messages to your objects. THAT is nice.

So, that is the way we cho0se to go: A new environment is created (a guest) into the current environment (the host).  The guest will have it’s own classes and objects.

What about the special objects of the vm?  We share them with the host environment, because if not, out new image will not be able to run… Afterwards, when this new image is written into an image file, we will swap references to point to our own new special objects array.

Here is a picture of how it looks like:

How the host and guest are related

The Current Version

I’ve been through several versions of the image with different capabilities, sizes, correctness. You have to know, everything you forgot to initialize, or initialize in a wrong order, or if you took an extra object you do not need, you will have a not running image, or one that carries all the objects in the host also…

Another thing is that current version takes a sample of the objects in the host to build the guest. I’m already working on starting from scratch + source code, but that is the future and I like enjoying the present :).

So, how do you load the current code?

Gofer it
    url: 'http://www.smalltalkhub.com/mc/Guille/Seed/main';
    package: 'ConfigurationOfHazelnut';
    load.

(ConfigurationOfHazelnut project version: '1.3') load.

Also, as the code is very sensitive on what you do,  it is also sensitive on what image you’re running it on.  If you play with it in a wrong/different image, you will have different/unexpected results.  So, I suggest you to use the same image as me for testing it: Latest Pharo 2.0.  In particular, I’ve tested it on versions 20133 and 20134.

Do not scare when loading the configuration on Pharo 2.0 for the first time It will raise an error. It is an issue related with unzipping old mcz in Pharo (http://code.google.com/p/pharo/issues/detail?id=6054) which will fortunately fixed soon. Just close the debugger, try again, and get the project working.

And, How do I try these weird stuff?

With Nicolas Petton, we have written some examples in the class named HazelBuilderExamples.

To run them, you can try the following scripts:

"Writes an image which when opened prints a spaceTally on fileok.txt"
HazelBuilderExample new buildImageWithSpaceTally

"Writes an image which when opened prints a report on all the packaging/initialization deficiencies of the image on fileok.txt"
HazelBuilderExample new buildImageWithBrokenReferencesReport

"Writes an image which when opened prints a report on all the packaging/initialization deficiencies of the image on fileok.txt. The report is written in the xml format Jenkins Junit plugin likes."
HazelBuilderExample new buildImageWithBrokenReferencesReportForJenkins

After evaluating this code, you’ll have some bootstrapped image and changes files. Open that file with your CogVM and wait until it closes.  Then have a look at the fileok.txt file :).

Of couse you can look at the code in the examples, and try to build your own. Email me if you have ideas to improve this :).

There are also probably some problems with file overwritting that came with some latest Pharo changes with the file management.  Please, if you notice this, just remove the bootstrapped* files from the folder where your image is and try again.

Hey! How is this thingy useful?

Well, if you’ve had a look at the examples, the three examples I’ve shown you are very useful:

  • The first one tells you how the space is distributed in the new image. You can use this knowledge to attack space problems if you want an even smaller image.
  • The second one is used to detect bugs in the pharo Packaging or in the initialization process: You have not initialized some classes, or the have been initialized but the initialization code does not initialize all the variables.
  • The third one is the same as the second, but adapted to have this kind of CI integration: http://car.mines-douai.fr/ci/job/Seed%20Broken%20References%20Report/

Nice huh? Now we can use jenkins to validate the core of Pharo is well initialized and well packaged when that list becomes empty.

What’s next?

  • Each one of those things in the list should be tracked as issues.
  • continue working on the bootstrap from sourcecode.
  • Making the fuel seed work so we can install fuel packages on our little image.

Keep u updated!

Hasta Luego!

Guille

The Bootstrap Chronicles Chapter 2 – Do not mess with the VM

Everything you want in life has a price connected to it. There’s a price to pay if you want to make things better, a price to pay just for leaving things as they are, a price for everything.

Harry Browne

And I found myself trying to bootstrap for real. But of course it was not going to be easy. I had to pay the Iron price.

The VM we use plays a very important role in the day to day development. It is the one in charge of defining the method lookup, garbage collection, some platform dependent code, some optimizations. And as it does some nice things for us, it also puts restrictions on what we do. Have you ever heard about the special objects array? The compact classes array? Primitives? We are going to talk a bit about them and other secrets, and how they bother in the bootstrap process :).

The Special Objects Array

The special objects array is an array shared between the VM and the image. This array points to some objects that are important or interesting to the VM, you can have a look at it inspecting the following expression in Pharo:

Smalltalk specialObjectsArray

If you have an overview, you will see some things like the Processor instance, the Array, Smalltalk, SmallInteger, Float, Compiled method, Semaphore classes, some Semaphore instances…

What does the vm do with them? It for example introduces hard validations against concrete classes -yeap, like checking if an instance’s class is the same as the object in it’s slot 20, which BTW is Character…

Ok…

Doing those validations through messages could be too expensive in terms of speed. If you want to be fast, you have to pay some price. If you want to have a tiny mermory footprint, you have to pay some price. There are side effects for decisions in general…

So, some may wonder, Why is this array so important for the bootstrap? Imagine I want to have a new Array class, Class class, Character class, and a new CompiledMethod class.  What should happen if the VM does not recognize them as I would like? CogVM only recognizes one special objects array.

The solution? Hack and cheat.  You choose, you can cheat on the VM side, or in the image side.  Each has a price to pay.  But today is not the day for telling you how I cheated :).

Now, look at the field 29 of the special objects array. It is another array, …

The Compact Classes Array

U remember about compact objects?  If not, you can refresh in here: https://playingwithobjects.wordpress.com/2012/05/30/understanding-object-formats-in-cogvm/.

In two words, compact objects do not have an extra header for the class pointer: they have some bits in it’s base header which is an index into this nice compact classes array, where it’s class is. This mechanism is normally used for classes with tons of instances, saving 1 header for each object. Complexity against space.

Here again, we have the same problem.  Even worse, having this guy here means that if I have my nice Array’ class, which is also compact, and it’s compact class index points to the original Array class, the method lookup will end up in the original class instead of mines :(.

The solution? Hack, and cheat.

The Primitives

Now think what happens when my bootstrap classes use primitives methods. It’s nice because the vm returns me the objects it wants :). It’s actually a sinptom of the last two points. But it is good to know that primitives can give you headaches…

Other problems? Of course…

Literals: I can’t change so easily SmallInteger’s class because it is an inmediate object for example. The same happens with the other numbers, or strings, or blocks.  They all give you headaches. Even if I could make it work with the VM, I should change the compiler to use a different set of classes…

Vm magic assumptions: Like class instances’ first three instance variables are superclass, method dictionary and format.  In that order. Try changing the order :).  Or doing something like:

myA := A new.
A become: 'hello'.
myA crashTheVM.

And there are some other like this. So far I know LinkedList, ProcessScheduler, and Class. Find your own Waldo!

You already know what the solution is, do you?

HACK AND CHEAT

Yeah, this is what the bootstrap is really about. And learning hardcore stuff too :). Of course I can’t tell you every detail because this post will be larger than anyone would care to read.

So, I’ll keep you updated, I have now to continue paying the iron price.

$33 ¥0µ £473r!

9µ1££3

The Bootstrap Chronicles Chapter 1 – Preparing the soil

In my last post I briefly explained what a bootstrap is and why it sometimes is necessary or good to have. But bootstrapping a system is not always the panacea: it means that you have to know lots of it’s internals, implement hackish stuff, fight against huge walls like the VM restrictions… So, today we will talk a bit about implementation.

The First Experiment

I started trying to generate a new image and people pointed to SystemTracer.  There was a fork on PharoTaskForces also, and there were some experiments to base my work on. So I had plenty of things to look at. To have an idea of what SystemTracer does:

  • Traces the whole image graph
  • For each object it reaches, writes a binary version on a file, respecting the object format
  • Finally, it comes to the start of the file and writes the header the VM needs to start

So my first experiment was based on adapting this SystemTracer guy to write a custom set of objects instead of the whole image. The chosen objects were the ones in the Kernel packages, compiler, files, collections…

First problem: If I cherry pick the stuff I want in the new kernel, and the packaging is crap, my selected classes can point directly or indirectly to objects in the non selected set.

This kind of behavior can mean several things:

  • You picked wrong.  You forgot to pick dependencies that should be there to let the image work. Or you picked stuff you didn’t need.
  • You picked right, but you have bad packaging in the system, and have to fix it.

You can be asking yourself, Why not following dependencies recursively? Because if you do that, you will end up with the the whole system again :), so simple. Then, we needed a way to trace these problems, instead of hiding them behind a carpet, because whatever the cause of the problem is, it is a problem in the original system we have to fix, not in our process.  The chosen solution was to replace rejected objects by a mock ones when writing the image through the SystemTracer. This mock object, which we called MissingVariable could carry some info for debug.

After some trials, I got this little monster alive, compiling stuff, writing to files…

But this is not a bootstrap. Because this process is not to make explicit initializations nor kernel creations. So, my next post will be about the next step: towards creating an image from scratch.

Au revoir!

Bootstrapping: finding the missing link

A few months ago I got involved in some crazy project: bootstrapping Pharo. I took some existing code, played with it, hacked it, modified it, understood it. Now I think I have some idea of what is a bootstrap and what are it’s advantages. I’ll try to give a brief introduction to the project: what is it about, advantages, an overview of the current military secret results, and an insight of what is to come.

I recommend you to have look at my last post (the image dilemma) before reading.

This project is one of the ESUG projects supported this year by the google summer of code program.

What is a Bootstrap

The encyclopedic definition: A Bootstrap of system is a process that can generate the smallest subset of that system that may be used to reproduce the complete one.

I mean, you have an explicit process that can generate a the minimal version of your system.

Ok, easier: You kick yourself to get impulse and start from a better place :).

Then, bootstrapping software systems or languages normally means that you will somehow enhance the original process that created the system.

Some examples to clarify:

  • When your computer is turned on, some one has to bootstrap the little program able to load other programs :).
  • Generating a development environment with very basic tools will improve your work a lot (when you use your development environment).
  • C compiler is written in C. That means that It somehow compiles itself. Of course if you do not like assembly much, reading the C implementation is a great improvement.
  • Pharo implements traits and uses them in the core of the system to empower the design.
  • A big part of Pharo’s VM is written in smalltalk!

The need of bootstrapping Pharo

Did you know the image you download from the pharo website is the same one that comes from years ago? I mean, not the exactly same one, but a binary copy :). The fact is that years ago (yeah, ancient history) god created the first image and it started evolving, one little change after the other, to the Pharo we know today.

Now, as in evolution, we found in Pharo missing links.  We do not know how some object became the way it is. Or how it was initialized.  The code is simple nowhere, it’s a missing link. Also, as years passed, our ancestor became chaotic. It grew in many different uncontrolled and unordered ways. Since the Pharo Project started, one if it’s goals was cleaning this mess, but re-modularising and cleaning the system is a hard, long, and bothersome process.

The outputs and advantages of Bootstrapping Pharo will be:

  • getting tools to detect problems: bad dependencies, unexistent initializations, code that really do not work but was never executed before.
  • This initialization process will be explicit and open.
  • We will be able to start the next Pharo from scratch, and since we will be able to change this explicit process, our next generation Pharo will be cleaner and fancier. It will be able to acquire easily new features: namespaces/modules, security, remote tools, mirrors.
  • But also, since it will allow people to create a custom system, researchers will have an invaluable tool to fulfil their own purposes.  They will be able to experiment

Current status of the project

The project has already had a first output, which is the image writer.  The image writer is a little tool that traces a graph from an SmalltalkImage object, and deploys that graph into a .image file.  I’ll talk about this sub project in a future post.

The rest of the code is a military secret yet. Ok, I can give it to you, but you have to be responsible if it blows up on your face :).

The results of the project so far are:

  • It can create an Smalltalk image living inside another image.
  • This inner/guest image can be written in a new .image file.
  • With this approach a small kernel of 1.1MB has been reached.
  • SpaceTally runs and prints reports to understand how the space is distributed among objects.
  • A tool to detect every uninitialized class variable/class instance variable and references to unexistant globals was developed.

Soon we will have all these public on Pharo Jenkins server.

Next Steps

  • Jenkins jobs :)
  • Taking jenkins feedback to speed up the cleaning process
  • Remodularizaton to get even a smaller kernel
  • Maybe some little experiment to bootstrap MicroSqueak and learn from it
  • Bootstrap from source code.

I’ll try to keep you updated often.  BTW, any ideas, critics or suggestions are welcome. I’m not a gurú, I’m just learning, as everyone :).

Saludos!

The Image Dilemma

Without self knowledge, without understanding the working and functions of his machine, man cannot be free, he cannot govern himself and he will always remain a slave.
Goerge Gurdjieff

Many people I’ve talked to think Smalltalk is weirdy because it has an image.  Funny thing is most people that thinks that, do it because they feel it’s different.  Or they do Java.  Of course, Java and Smalltalk are different :). Okok, joke, I’m not interested in flamewars. Seriously what puzzles me is that normally people’s opinion on technology is based on feelings instead of concrete rational arguments.

So, let’s think a bit on the pros and cons of using an image and not using it.  Really. Only after understanding a bit you can decide whatever you want to use. That’s what the quote at the start is there for :).

Also, this post will be one of the corner stones to explain the bootstrap gsoc project basics later ;).

Non Image Based Development Environments

Ok, we all know these. It’s the kind of environment we use when we code in C, Java, Python, Ruby, JavaScript and many other.

We have source files which will be somehow interpreted on runtime or traduced to machine code in an executable file.  Naively explained, the interpreted ones normally depend on another program normally called interpreter or VM and the other ones depend only the first time on a compiler. So far, nothing strange.

Image Based Development Environments

Image based environments are the main topic of this post.  But before talking about it’s pros and cons, we have to define what is an image. And to avoid preconceptions, let’s name them snapshots. A snapshot is a photo taken of a system in a moment of time x, from which we can rebuild the whole system again.

If you have ever used VirtualBox or VMWare solutions you know what I am talking about: you have, for example, a linux mint virtual machine, which can be opened with your virtual box software.  If you save the state of your linux mint with virtual box, the next time you open it, it will wake up in the same state you left it. It will not start everything from scratch unless you tell it explicitly. And if you quit without saving, the next time will open without your changes.

It’s a very simple concept:  you are treating a whole running system (a linux machine in this case) as any of your other data files.

So that’s how most of the smalltalk systems work: you have a running smalltalk system, and when you wake it up, it will start from where it was left. Even if you was in the middle of a computation, this computation will continue running.

Comparison

System Configuration

How heavy or reproducible is our system configuration?

non image based

When a program start it normally does some basic initialization, configuration loading, setup stuff…  Every time our program does this same basic stuff.  It’s a repetitive task, but it’s done by the machine, so I’m ok with it.

Even more, one of the advantages of loading the application again from scratch is that you are testing your building process. And having a working artifact after ensures that you will be able to rebuild it in the future following the same steps.

But have you ever wondered how much time takes a java class loader to load the classes you will use?  And how much time takes Hibernate or Spring or JBoss to read your configuration, and provide an usable environment?  And how about to compile a large C/C# application? Ok, those times are machine time. You can go to take a coffee every time you restart your tomcat, or change a source file with many dependencies. That time is not even important in a deployed product, since it is delayed to the user or webserver which may run it once every hours/days. But it is important some times.  For example, when you are developing software. Software development is a highly demanding task which requires concentration. Taking a coffee every 15 minutes makes you lose concentration. And you can’t avoid checking/compiling/testing your code for long periods of times because handling lots of changes only in your head it’s a really hard task.

image based

When an snapshot is taken, the whole objects and computations that were occupying some memory in your program will be saved in a file in the state they were.  Object references are not broken. Then, when you load your smalltalk snapshot again, the objects take place in memory, and continue working as they were.  Normally there is not heavy initialization on image startup other than reallocating resources from outside the environment (files, sockets are OS resources and become invalid for sure when the system is halted).  You don’t have to configure almost none of your program neither, because it is already configured!

Now, since you don’t have to reinitialize your configurations from scratch every time, maybe you initialized it, then accidentally deleted the method that performed the configuration. And then you are screwed, because if you want to start from scratch you will have pieces of your program lost that will make it impossible.  This is why we may consider an image based system and evolving environment.  Because the system is changed by mutations that may get lost or untracked.

The Development process

How is our development process altered by the environment we use?

non image based

  1. Write code in a file
  2. Compile or similar or however you want to call it :).
  3. Run the whole program from scratch
  4. Test
  5. Go to 1

This process is slooow.  Specially because of steps 2/3.  For every change you do, no matter if it is long of little, you have to rebuild everything and lost time with it, and reinitialize, and reconfigure…  Even if you only wanted to replace a 2 by a 3, or fix a typo in a string.

However, there exist currently some tools that implement what they call hot deployment which is nothing else that exploiting some dynamic features that let a program change while it’s running.  But hey!  That’s what we do with an image based approach: we change the program while it’s running.

Anyway, those extra steps makes you gain reproducibility by making some parts of the process a bit more explicit.  At the cost of extra bureaucracy.

image based

  1. Open your image
  2. Write code
  3. Evaluate/Accept
  4. Test
  5. Go to 2

Here the main difference is that the modification of our program is made of little deltas during execution.  We replace/change/create methods while our whole program is running.  We create classes, objects, modify class hierarchies while our whole program is running.  We alter our objects state while our whole program is running. This really improves the development process, since the time you have to wait to receive feedback from execution or testing is almost none. And there is less overhead, less context switch in your head.

Now the problem is that to reproduce our program we have to track all the little changes we’ve done.  And understand them, and discard the ones that really overlap o do not make sense.  In the Smalltalk System Pharo we have a .changes file that works as a log of the changes done.  This changes file aims to reduce the impact of this dynamic feature disadvantages.

IDE’s Features

Have you ever used an IDE with refactoring support, syntax highlighting, nice code browsing capabilities?  What do our tools need in order to provide us all those gourgeous features?

IDE are meta-programs. They are programs that help us manipulate programs: modify them, understand them, query them.  And to do that they can do it by:

  • directly modifying source code without a model behind.  Painful and Hard.  I would never try to do it that way :).
  • modeling the concepts of the language they will manipulate to make it easier.

non image based

A program’s meta model (a model representing program entities such as classes or variables instead of domain entities like bank accounts and clients) is often generated when the program runs if you have reflective capabilities in the manipulated language. But IDEs should work while the program is not running, or even if it does not provide reflection. So, how does this approach build this kind of tools?

They have an alternative model and an alternative parser/compiler which generates this model from sourcecode.  A lot of extra work is needed for information that is already there. The problem is that information is lost in text files with source code instead of being stored in a more malleable format.

image based

Our image based approach can contain all the meta information in the snapshot, alive, as first class objects.  This means that we do not have to create a duplicated meta-model, nor an extra parser/compiler.  We can use the ones that are alive in the image.  We make use of the model created by the language, what we can’t do in the non image based approach.

Files or no files

Some times you feel comfortable modifying files, some times not.

non image based

You have files with your source code. You can use them to execute/compile your program, you can store them in svn/git/bazar repositories, you can diff/grep/more/less/find over them just using a terminal.

I think this is the main pro over the image based approach. There are plenty of tools working on plain text files you can use if your source code lives in this kind of storage.

But try to write a program implementing an extract method refactoring over a piece of text.  You have to write a very complex and large program analyzing classes, methods, scopes…

In two words: It’s really cool to use existing tools.  But it is not that nice to write your own.

image based

As the opposite of the not having an image, we can’t just use our nice text manipulation tools on our image file.  We have to rebuild them on our system, or externalize the source code in files to use them.  And then re-insert the feedback in the system.

But there are other tasks-like refactorings and meta programming in general- that become very simple just by the fact of manipulating objects instead of text.

In the Pharo project there are plenty of existing and arising tools aiming us to interact with the outer world, just like:

Conclusion

As I’ve shown you, these two approaches have their good and bad stuff.  None of them is the silver bullet, and we should be aware of that to be better developers.

I hope you are a little more free now ;).

さようなら!