Re: last item. no output

OK. Now you're problem is much clear.

Have a close look at the type inferred for last.

val last : 'a list list -> 'a list = <fun>

This is due to your first match case: if your incoming list is void, you are returning a void list as last element.

It has to return lists in the other cases. So does it.

Which means that last is waiting for a list of list of something: 'a list list


The problem is asking you to take a list of something ('a list), and return either that there is no last
element (None) or that there is one element (Some something).

val last: 'a list -> 'a option

Have a look at what option is.

Salutations

-- 
Matthieu Dubuget
Guide d’autodéfense numérique : http://guide.boum.org


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