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[Caml-list] Discarding elements from a list
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Date: 2003-01-26 (19:00)
From: oliver@f...
Subject: [Caml-list] Discarding elements from a list

after Remi has pushed my towards rewriting my
"I do it like I know it, and therefore imperative"
version of a program into a functional version of
this program (thanks, Remi, I have explored a lot
new things since then :)) I sometimes come to
this problem:

I have to use a partial list.

In the reference manual I did not found any
stdlib-function, and so I have two ideas,
of how to perform e.g. a list, which is used
without the head (throwing away first element):

a) Converting the list to an array, shorten the array,
   converting back to a list, using the list in a functional

b) Using pattern match to throw away the first element, then
   working in the part after the "->" with a function, which
   works on the rest of the list.

c) using a function, which uses an index, for counting, at which
   position we are inside of the list

This problem arises, when a list, on which should be worked,
will be created and it must be used a part of it (e.g. all
elements but the last or all elements but the first), like
creating a multiplication of the last and the current element...
(like fibonacci uses addition, I need multiplication here)
and when the first or last is necessary for some calculation,
but should be thrown away for some other calculation.

Because I have no criteria to decide, which solution I should
prefer (and why), I always rethink the problem again,
and the decision-process slows down.

So, why should I use which solution?

(And how to select parts of a list in general, not only
 throwing away the first or last element?)

Any hints?

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