[Haskell-beginners] Are these soloutions all valid and a good use of Haskell

Roelof Wobben r.wobben at home.nl
Mon Nov 10 13:28:08 UTC 2014

I tried and so far I have this :

last5 = foldl(\acc x -> if x=[] then x else acc xs) [] xs

But now I get parse error on the -> part.


Roelof Wobben schreef op 10-11-2014 13:47:
> Thanks all,
> I will try to make a fold solution as soon as I see that functional 
> explained in the learnyouahaskell.
> Roelof
> Frerich Raabe schreef op 10-11-2014 11:43:
>> On 2014-11-10 11:16, Karl Voelker wrote:
>>> On Mon, Nov 10, 2014, at 01:50 AM, Roelof Wobben wrote:
>>>> What do you experts think of the different ways ?
>>> 2 and 4 are quite similar, and both fine. 3 is not so good: guards
>>> provide weaker guarantees than patterns, and head and tail are partial
>>> functions.
>> In addition to what Karl wrote, I'd like to suggest not using the 
>> semicolon all the time -- it's not needed and just adds noise.
>>> All three implementations have in common that they do their own
>>> recursion. It would be a good exercise to try implementing last as a
>>> fold - in other words, letting the standard library do the recursion 
>>> for
>>> you.
>> Right - I suggest trying to express the problem with the most abstract
>> function first, then consider using a fold, then use manual 
>> recursion. in
>> your particular case you could exploit that for non-empty lists, getting
>> the last element of a list is the same as getting the first element of
>> a reversed list (and there are ready-made functions for reversing a list
>> and getting the first element of a list).
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