On 2/13/12 4:20 PM, Stephen Bloch wrote:
On Feb 13, 2012, at 8:28 AM, David Van Horn wrote:
In BSL, you can detect when the first element of a clause is a variable bound
to a function, but I don't follow the reasoning about ISL. You can't
distinguish good from bad uses without running the code because you can't tell
if a name refers to a function or a non-function.
Not reliably, because the student COULD be using a parameter or a local
variable in that position. But in the COMMON case of this error, the student
will use a predefined function or an explicitly user-defined top-level
function, and it should be possible to recognize those at syntax-check-time.
But even if the name is a parameter, it cannot be bound to a function.
If it's a local, it either is or isn't a function -- you can tell from
the definition.
I think it's correct to consider this a syntax error, not a run-time
error. It should just have a better message.
Which leaves
cond: question result is not true or false: (lambda (a1) ...)
as a good error message to report at run time in the rare cases that don't
match the above description.
Except you don't want to say lambda in BSL.
David
_________________________
Racket Developers list:
http://lists.racket-lang.org/dev
