use Perl

• unfoldr (Score:1)

  by int32 (6174)

  I played a bit with the concept, and found an issue I can't resolve, possibly you can help me here. The problem concerns whether $_ is an alias or a copy to the parameter passed. If it is a copy then you can't modify it unless it is a reference. If it is an alias you can't modify it if it is read-only. You may ask why should it be modified at all, and here comes the classic unfoldr:

  unfoldr { $_ ? ($_, $_ - 1) : () } 10;

  10,9,8,7,6,5,4,3,2,1

  which allows to pass arbitrary values to the callback .
  • Re:unfoldr (Score:1)

    by Aristotle (5147) <pagaltzis@gmx.de> on 2009.01.29 17:53 (#67111) Homepage Journal

    Btw, no, your point about alias vs copy is mistaken. The induce function above takes a copy of the value and then aliases $_ to that copy, so you are guaranteed to be able to modify the value, although if you want to preserve its last value past the unfolding, you want to arrange for that yourself.

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