[plt-scheme] Student parsing problem

From: Jay McCarthy (jay.mccarthy at gmail.com)
Date: Tue Jun 2 17:36:38 EDT 2009

Yes, that would work for Beginner. But for the syntax highlighter, I
don't think there's a nice way. My final sentence's "but" should only
apply to the right-hand side of the "and".

I'd change Beginner to show ya'll, but from what I can tell it use
parameters to communicate the different syntax to the real C-reader.
So I'd need to muck with that and add a new parameter... very messy
and not sure its what the Powers That Be would prefer.


On Tue, Jun 2, 2009 at 3:33 PM, Carl Eastlund <carl.eastlund at gmail.com> wrote:
> On Tue, Jun 2, 2009 at 5:27 PM, Jay McCarthy <jay.mccarthy at gmail.com> wrote:
>> I just helped a student debug their program. It looked like this:
>> (define (function1 arg)
>>  ...
>>  )
>> `;;(html (body "Text"))
>> (define (function2 arg)
>>  ...)
>> (function2 1)
>> Naturally it is easy to tell that the problem is that ` finds the next
>> s-expression, even if there are comments and whitespace between it and
>> the next one; so function2 isn't really defined at all.
>> Now, it seems reasonable for this to be a problem that the user should
>> deal with in the Module and other higher languages. But you can get
>> the same problem in Beginner (w/ List Abbrevs):
>> (define (foo bar)
>>  1)
>> `;; Example
>> (define (zog zag)
>>  2)
>> (zog 1)
>> It would be nice, IMHO, if Beginner restricted ` and ' to be adjacent
>> and the standard syntax Scheme highlighter in other languages made
>> quoted expression visually distinct, but it doesn't appear that that
>> is easy to do without trying to do a full parse, plus there is the
>> obvious macro problem.
>> Jay
> This sounds like a custom reader problem to me, which avoids all
> issues of parsing in the editor and "macro problems".  "Just" make it
> a read error to have whitespace, comments, etc. between ` or ' and
> their subsequent, implicitly-wrapped s-expression.
> --Carl

Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University

"The glory of God is Intelligence" - D&C 93

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