[plt-scheme] Student parsing problem

If there's evidence that students get bitten, I think we should do  
something about it.


On Jun 2, 2009, at 6:55 PM, Carl Eastlund wrote:

> I have had students run into the same problem with #; comments, that a
> #; before whitespace or another comment could be forgotten.  I think
> all of the s-expression-eating reader forms should have the "no
> whitespace/comment" restriction in the student languages.
>
> --Carl
>
> On Tue, Jun 2, 2009 at 6:37 PM, Matthias Felleisen  
> <matthias at ccs.neu.edu> wrote:
>>
>> This is an interesting error, and as a beginner I ran into this  
>> myself
>> (1984, probably february or march :-)
>>
>> I have not seen this kind of error since then, however. Before you  
>> invest
>> time, let's see how many people have had students who stumbled  
>> over this.
>>
>> -- Matthias
>>
>> On Jun 2, 2009, at 5:36 PM, Jay McCarthy wrote:
>>
>>> 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.
>>>
>>> Jay
>>>
>>> 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
>>> http://teammccarthy.org/jay
>>>
>>> "The glory of God is Intelligence" - D&C 93