Thank you for finding MapCar. That does a lot of what I need.

So yeah, I just realized that fold_left can be written by simply calling reduce with the same arguments (so that fold_left's initial becomes the first element of reduce's input). But fold_right does require two reverses, in the following sense: suppose I wanted to compare left- and right-associative subtraction. Then, I have to reverse once to change a call of fold_right into fold_left but then I also have to change the order of arguments into the block.

Well, I really want sum to be reduce { $a + $b } 0, @input, so that would make multiplication reduce { $a * $b }, 1, @input. Note that sum is not reduce internally. Here's the code: 

sum(...)
PROTOTYPE: @
CODE:
{
    SV *sv;
    int index;
    if(!items) {
        XSRETURN_UNDEF;
    }
    sv = ST(0);
    RETVAL = slu_sv_value(sv);
    for(index = 1 ; index < items ; index++) {
        sv = ST(index);
        RETVAL += slu_sv_value(sv);
    }
}
OUTPUT:
    RETVAL

[download]

In reply to Re^2: More functional programming utilities by kaif
in thread More functional programming utilities by kaif

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.