Guillaume Marceau wrote:
Right now, the stepper takes the code from the definition windows and
displays it in a different window, with a different color, with a
different layout, with some brackets turned into parenthesis, and with
the comments are removed. I just opened a simple solution from last
semester and launched the stepper on it. It took me no less than 20
seconds to trace the first redex presented by the stepper to the
expression in the definition window it came from. It's really hard to
do!
When using the stepper, students struggle to see the correspondence
between what's on the left and what's on the right, despite the
colored highlights and all that. In my experience, the correspondence
has to be carefully pointed out to them by the instructor. Their
understanding of the correspondence between the content of the stepper
window and the code they wrote in the definition window must be
fainter still.
There has to be an easy way to establish these two correspondences:
from pre-step to post-step, and from the stepper window to the
definition window. None of the proposals posted to in this thread so
far address this.
I can think of many different ways to make the stepper<->definition
correspondence manifest. As John said, I once suggested that the code
should be reduced in-place, in the definition window. Shriram doesn't
like that idea (but he has never bothered to say why.)
Another possibility is to use a two column layout. The left column
would show the normal definition window, and the right column would
show a single stepper state, aligning each reduced (or partially
reduced) expression with the expression it came from on the left-hand
side.
To establish the pre<->post correspondence, the redex should disappear
and its reduction be put in its place (with the rest of the code
sliding downward smoothly to make space if necessary.)
Another, less invasive, way of making the stepper-definition connection
might be on every step to scroll the definitions window and highlight
the term from which the redex is derived. For function application the
function definition could be highlighted too in a different color. The
highlighting would require some creativity for forms like cond (maybe
de-highlight clauses as they're eliminated?), but it would be a more
incremental approach than forcing the stepper UI into the definitions
window.
Ryan
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