The impact of moldability

We say that Glamorous Toolkit (GT) is a moldable development environment. There were a couple of emails on the Pharo mailing list in the recent period that questioned the usefulness of moldability. More specifically, the questions were raised in relation to the newly introduced GTDebugger. The concept of a moldable debugger is new to any IDE, and for this reason we cannot compare with the standard IDE behavior.

Nevertheless, the question is certainly legitimate. Given that we cannot compare with other solutions, we can observe the impact of other moldable interfaces. If we take a step back, the same concept was applied to the GTInspector and GTSpotter before. We introduced these in Pharo 4.0. Let’s see what is the impact.

In Pharo 3, the EyeInspector offered a basic extension possibility, and the Pharo image shipped with 8 such extensions. Together with the introduction of the GTInspector, we shipped 138 extensions. One year later we have 165 in the core image. In the meantime there are many more extensions in external packages. For example, the Moose 6.0 image which is based on Pharo 5.0 ships with about 230 extensions.

Also, in Pharo 4, we shipped 92 extensions to GTSpotter. In Pharo 5, there are 122 extensions. Similarly, there are several more extensions in external packages. For example, in Moose 6.0 we have 135 and if we include the generic way of searching through models we have several hundred more (more about this in a future post).

The explosion of extensions shows that there is a need to have such extensions. This is a validation of a hypothesis put forward by the humane assessment approach a long time ago which started from the observation that context is key in software development, and as such, tools should take this context into account. This idea was first explored in the context of Moose and it stands at the very core of GT. You can see this embodied now in 3 distinct tools, and we will see more as we proceed with the project.

Now, why the difference between Pharo 3 and Pharo 4? First, the cost associated with an inspector extension went down from ~19 lines of code in a separate class to ~9 lines of code in one single method. Second, the value of the extension increased because of the interaction workflow that came with the GTInspector design.

Interestingly, after we introduced the GTInspector, almost all discussions were geared towards the Raw presentation because it introduced a new kind of interaction. Almost no email was about the extension mechanism. The same pattern happened with GTSpotter where messages focused almost exclusively on searching classes and methods. And rightly so, as the default behavior is what people see at first. We have exactly the same type of issues with the GTDebugger.

Now, in the default Pharo image, there are 3 different debuggers: the default one, the bytecode one and the SUnit one. In the Moose image there are 6 debuggers and there are a couple in outside packages. For example, here are two screenshots of two such debuggers: one of a PetitParser debugger, and one of a debugger debugging the update of the debugger.


The cost of these debuggers is measured in hundreds of lines of code. We will certainly not see as many debugger extensions as in the case of the inspector because the granularity is larger and because the cost is larger, but we will certainly see more custom debuggers.

We still need to learn more about how to reach the balance between extensibility and usability. We are at the beginning, but there is clear value in extensibility and we should not discard it as unimportant. The key here is the ability of creating extensions with low effort and this is unprecedented. Let’s put this in perspective: Eclipse started more than a decade ago with a plugin architecture. Right now, the Eclipse marketplace ( has 1722 tools. Granted these are more extensions than we have and they are larger, but at the same time the community that builds those is several orders of magnitude larger than the Pharo one. Yet, we can already compete with this because of the radically low cost structures.

Until now we looked at quantitative plain data. Nevertheless, are these extensions actually affecting productivity qualitatively? In my experience they can have a significant impact, and this site and blog features multiple examples of how this is so. Furthermore, more recently I realized that my workflow has changed quite significantly and the amount of time I spend in the inspector is around 60%.

But, let me give you another perspective. I went around the world over the past year and I asked directly more than 1000 developers working in various languages if they agree that they read code for 50% or more of their time. The vast majority agrees (this is on top of research showing the same thing). Yet, when I ask them if they talk about it to find new ways of understanding systems, they acknowledge that they almost never do. This basically means that people are spending half of their budget on something they never talk about. These are just the direct costs, and many systems see some 80% of their overall effort spent in maintenance. Understanding systems is the single most expensive activity, but the industry does not approach this explicitly. And typical IDEs focus to a large extent on the active part of creating code. For example, is it not ironic how in all IDEs the reading happens in an editor? In Pharo, we look at this problem in a novel way and we have the chance of affecting business costs radically.

Moldability is a competitive advantage. This is why we would like to encourage people to play with these mechanisms and push the envelope of software engineering.

Posted by Tudor Girba at 4 June 2016, 6:16 pm with tags assessment, tools, gt, pharo, moose link