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.

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