[plt-scheme] Some fine distinctions

Which one is not?

On May 13, 2009, at 8:40 AM, Robby Findler wrote:

> Actually not every call to sumlists is in tail position.
>
> Robby
>
> On Wednesday, May 13, 2009, Matthias Felleisen  
> <matthias at ccs.neu.edu> wrote:
>>
>> On May 13, 2009, at 7:24 AM, wooks wrote:
>>
>>
>> Didn't fully absorb that. So
>>
>>
>> sumlists :: listoflists -> number
>> (define sumlists
>>    (lambda (a-list)
>>       (let sumlists ([a-list a-list] [accum 0])
>>         (cond
>>          [(empty? a-list) 0]
>>          [(list? (first a-list)) (sumlists (rest a-list)
>>                                   (+ accum (sumlists (first a- 
>> list)))]
>>          [else (sumlists (rest a-list) (+ accum (first a-list)))]))))
>>
>> This is accumulative and I used to think ergo tail recursive.
>> If I am right and it is not (because of the evaluation of the list?
>> case)...is there any way to write this sort of function tail
>> recursively. It looks to me not... at least not in this style of
>> programming.
>>
>>
>> Every call to the (inner) sumlist is in tail position, ergo this  
>> function is tail-recursive.
>>
>> ;; ---
>>
>> The accumulator statement is
>>
>>  ;; accum is the sum of all numbers between a-list0 and a-list
>>
>> (Of course, you failed to name your parameters properly so go back  
>> to the original reply and check it out.)
>>
>> ;; ---
>>
>> What I am saying is that accumulator-style does NOT imply tail- 
>> recursion.
>>
>> _________________________________________________
>>  For list-related administrative tasks:
>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>