isbn9789526046266

print third
second = third
print second
And here is a passage that illustrates a fairly typical way of working on this code in VPS:
Pair 33 have just reached the line third = second.
Kate 33 : Then ‘third’. . . ummm. . . we make a new one again. And then I do this. Creates the
variable and assigns the reference to it.
John 33 : Yup.
Kate 33 : And then number three from ‘second’.
John 33 : We take the third value. . . or the third term.
Kate 33 : Carries out the list assignment. Yeah. Then we print again. . .
John 33 : Small laugh.
Kate 33 : In a sarcastic tone: Exciting! Carries out the first print statement. Okay.
John 33 : All right. . . and then again, the ‘third’...
Kate 33 : So. . . Carries out the second print statement.
John 33 : [That was] the ‘third’ value.
Kate 33 : And again we change them.
John 33 : ‘second’ is changed to ‘third’.
Kate 33 : Yeah. . . Moves the cursor around the operators area. Oh yeah, there isn’t an equals
sign here. Or are we supposed to just drag this over here? Assigns from second into third.
No. It can’t be this one either, right? Tries using the assign-to-index operator. No, did I just
do it the wrong way around now?
John 33 : ‘third’. . .
Kate 33 : Assigns from third into second. That’s how it goes, yeah.
John 33 : Yeah.
Kate 33 : And then another ‘print’. Yay. Executes the last print statement. The end of the
program is reached and the assignment is complete.
John 33 : Yes! Ooh, yeah!
Kate 33 : Yesss! Next example. Opens the second VPS assignment.
At no point during the VPS session did Pair 33 pay any attention to the fact that two references point
at a single list in the heap. At no point did they pay any attention to how this is demonstrated by the
program output (or indeed pay attention to the output at all). Nevertheless, they selected each execution
step correctly and eventually completed the exercise without great trouble.
At no point did the VPS exercise require students to understand reference semantics in order to find
the correct simulation step. The students had no trouble with references not because they understood
the concept well but because there was no particular reason for them to pay attention to it. Most of the
students we observed simply ignored the topic entirely or took it for granted.
In the light of the above, and of existing research supporting active learning, it seems reasonable to
conclude that a significant part of the reason why VPS did not help students learn much about reference
semantics lies in how the VPS assignments did not require them to use their knowledge of the topic.
Other factors may also have contributed to students’ lack of attention to references. The visualization
of references in UUhistle v0.2 (see Figure 16.1 on p. 262) is not very attention-grabbing. The toylike
nature of the example programs may have made program output (which highlights the impact of reference
semantics) less interesting for the students. In a single case (described in Section 18.2.3 above), we saw
a pair consciously decide against believing the system’s visualization of references.
Despite the problems, some students did pay attention to references. Pair 6, whose work on the same
code is described on page 307, is one of these rare cases.
19.4 VPS helps with – and only with – what learners focus on
Let us try to summarize our findings. Our experimental study enables us to answer the question: “Does
VPS in UUhistle v0.2 work?” with a cautious “Yes, but. . . ” The system appeared to help students learn
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