Oh gosh...I missed that completely...Thanks Lindsay...That explains
everything!
I'm really pleased you told me that because drop looks like a really useful
function.
Best Regards
Dean

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On 6 February 2017 at 22:27, Lindsay John Lawrence <
lawrence.lindsayj...@gmail.com> wrote:
> P16 (**) Drop every N’th element from a list.
>
> (de drop (Lst N)
> (make
> (for (I . X) Lst
> (unless (=0 (% I N))
> (link X) ) ) ) )
>
> : (drop ’(a b c d e f g h i k) 3)
> -> (a b d e g h k)
>
> 'drop' is the function given as a solution to the problem.
>
> /Lindsay
>
>
> On Mon, Feb 6, 2017 at 1:24 PM, dean <deangwillia...@gmail.com> wrote:
>
>> Hi Alex
>> : (filter prog2 (1 a 2 b 3 c) '(T NIL .))
>> -> (1 2 3)
>> : (filter prog2 (1 a 2 b 3 c) '(NIL T .))
>> -> (a b c)
>>
>> Yes the above is exactly what I'm after.
>>
>> I copied this drop example straight from ninety nine..
>> ? P16 (**) Drop every N'th element from a list.
>> : (drop '(a b c d e f g h i k) 3)
>> !? (drop '(a b c d e f g h i k) 3)
>> drop -- Undefined
>>
>> I'm not sure why I'm getting "undefined".
>> I'm using the pil in my picolisp directory.... which looks like this....
>> exec ${0%/*}/bin/picolisp ${0%/*}/lib.l @ext.l "$@"
>> i.e. not the one in /bin which contains /usr,,,, which I think ISN'T
>> local and I think I compiled a local version.
>>
>> Irrespective....thank you very much for your solution.
>>
>> Best Regards Dean
>>
>>
>> On 6 February 2017 at 15:24, Alexander Burger <a...@software-lab.de>
>> wrote:
>>
>>> On Mon, Feb 06, 2017 at 12:25:14PM +0100, Alexander Burger wrote:
>>> > > I'd like to split a list '(txt1 2 txt2 6....
>>> > > into 2 lists
>>> > > '(txt1 txt2...
>>> > > and
>>> > > '(2 6
>>> >
>>> > You could for example filter them:
>>> >
>>> > (let
>>> > (Lst '(txt1 2 txt2 6)
>>> > A (filter sym? Lst)
>>> > B (filter num? Lst) )
>>> > ... use A and B ...)
>>>
>>> It is not clear what you need.
>>>
>>>
>>> If, for example, you want every *second* element, there is a nice trick:
>>>
>>> : (filter prog2 (1 a 2 b 3 c) '(T NIL .))
>>> -> (1 2 3)
>>>
>>> : (filter prog2 (1 a 2 b 3 c) '(NIL T .))
>>> -> (a b c)
>>>
>>> Similarly, you can extract other sequences if you pass the right pattern
>>> of
>>> NIL's and T's.
>>>
>>> ♪♫ Alex
>>> --
>>> UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe
>>>
>>
>>
>