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

That function looks right to me. What is going wrong?

Robby

On Tue, Jul 14, 2009 at 10:32 AM, Matthias
Felleisen<matthias at ccs.neu.edu> wrote:
>
> This is in svn head and tested, but I am pretty sure this worked in 4.0
> already.
>
> (Your function definition, if it worked syntactically, would be wrong.)
>
>
> On Jul 14, 2009, at 11:03 AM, Prabhakar Ragde wrote:
>
>> Matthias Felleisen wrote:
>>>
>>> Agreed, showing them pattern matching late but still in the first year is
>>> the right thing.
>>> BSL, with list abbrv:
>>>>
>>>> (require scheme/match)
>>>>
>>>> ;; [Listof Number] -> Number
>>>>
>>>> (check-expect (sum '(1 2 3)) 6)
>>>>
>>>> (define (sum x)
>>>>  (match x
>>>>    [`() 0]
>>>>    [(cons fst rst) (+ fst (sum rst))]))
>>>
>>> Enjoy -- Matthias
>>
>> Is this 4.2 where you can (require scheme/match)? I'm still at 4.1.3
>> (waiting for 4.2.1), and I can't. If I put
>>
>> #lang scheme
>> (provide match)
>>
>> in matchmodule.ss and then (require "matchmodule.ss"), I can get your code
>> to work. However, this doesn't work:
>>
>> (define (sum x)
>>  (match x
>>    [`() 0]
>>    [`(,fst ,rst ...) (+ fst (sum rst))]))
>>
>> I get:
>>
>> fst: name is not defined, not a parameter, and not a primitive name
>>
>> That last bit of code works fine in Module. --PR
>
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