[Pharo-dev] Suggested Syntax Highlighting Features for Beginners

J.F. Rick self at je77.com
Fri Apr 4 11:42:00 EDT 2014

Smalltalk is a pretty great language, but its syntax is unusual. I've
taught introductory programming in Pharo three times and, in my experience,
there are two places where novices get repeatedly confused with syntax.

First, there is the differences between assignment := and comparison = .
Obviously, Smalltalk is not the only language where that is a problem. Java
is even more confusing, with assignment = and comparison == . In Squeak,
there was the attempt to address this problem head on with using _ instead
of := and having it show up as an arrow pointing left; while that nicely
addressed that problem, it proved awkward for many reasons (e.g., it only
appeared as an arrow in Squeak, it wasn't compatible with other
Smalltalks). In addition, comparison is a simple message send, where
assignment is the most critical language element that is not an object or a
message. In other words, there is a huge difference in meaning between the
two and a really minor syntactical one. That's confusing to novices. Even
after covering it repeatedly in class I still find novices making that
mistake. As their debugging skills are minimal, this can be a real obstacle.

Second, there is the problem of keyword messages with more than one
argument. In Java, "this.someMessage( arg1, arg2)" is pretty comprehensible
to a novice. In Smalltalk, "self someMessage: arg1 and: arg2" seems like
two message sends (i.e., "this.someMessage(arg1).and(arg2)"). While novices
won't see multi-argument messages very often, they do come up (e.g.,
ifTrue:ifFalse:). I have my class do regular quizzes on identifying
messages and this still tricks them up even if they've already seen in 10

Now, I'm not advocating changing the Smalltalk syntax; that's just unlikely
to happen. But, perhaps syntax highlighting could be employed to good use.
For instance, it is extremely helpful that blocks and parentheses show by
color which ( [ go with which ] ). Perhaps something similar could be done
for messages with more than 1 argument. For instance, the message could be
underlined in different colors. That way I could easily see which ifFalse:
went with which ifTrue:. It would also give a visual indicator: (for
novices) Be careful, this message is one of those weird ones that's longer
than it first appears. For assignment vs comparison, you similarly need a
powerful visual cue that assignment is an usual thing, where comparison is
a pretty ordinary thing. Perhaps an arrow decoration could appear behind
the :=.

These may seem like trivial issues. For experts, they are. I don't need any
of it. I don't find syntax highlighting and command completion that useful
in my programming. But, I'm proficient with a debugger. Should I
occasionally make such a trivial mistake (e.g., forgetting to type : in
:=), I immediately find it while debugging and easily fix it. For novices,
using a debugger is not an option. Remember, they don't understand what a
stack is. Syntax highlighting is the best debugging feature that they
understand. And these are two real common mistakes that they make that
could be addressed by improvements to syntax highlighting.

Just a suggestion,


Jochen "Jeff" Rick, Ph.D.
Skype ID: jochenrick
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