[plt-scheme] A data point on 'match' in intro programming: +++!

From: John Clements (clements at brinckerhoff.org)
Date: Tue Jul 7 12:26:23 EDT 2009

On Jul 7, 2009, at 9:15 AM, Prabhakar Ragde wrote:

> John Clements wrote:
>> I'm leading high-school students through the construction of a  
>> bare- bones "universe.ss" application that models the prisoner's  
>> dilemma,  and I decided to import 'match' using a teachpack.  My  
>> experience thus  far has been completely positive, and if there's a  
>> drawback to using  'match' to replace structure-reference functions  
>> and predicates, it  hasn't come up.
>> Well, actually, I suppose I can imagine the following objections:
>> - a straightforward import of 'match' doesn't support symbol  
>> patterns  (presumably, it's a different "quote").
>> - you can't do nifty higher-order things with predicates and  
>> structure  reference functions.
> It would be nice if these could be fixed. In the "advanced" first- 
> term class I teach to really good students, I could use match pretty  
> early, except that I've never been able to get it to do the things I  
> want when I try importing it into a teaching language (I definitely  
> want symbol patterns and predicates). As it stands, I have to  
> introduce it after we move to Module about halfway through, and  
> that's later than I'd like.

I think you're misunderstanding me, though I now see that what I said  
wasn't well explained.  The point about symbol pattterns stands, but  
you *can* write structure patterns just fine; all I was suggesting was  
that if you introduce structures in this way, then when you want to  
show the kids how to use filter to extract all of the llama's from a  
list, you have to explicitly introduce 'llama?' or let them write it  


> I think match as a shorthand for destructuring parallels list and  
> quote notation as a shorthand for structuring, and can be introduced  
> after some explicit practice with accessor functions.

That's the traditional approach (IIUC), and it may well lead to better  


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