Ja, REST is CDR, basically (and FIRST is CAR). The Common Lisp HyperSpec says “rest is often preferred stylistically over cdr when the argument is to being subjectively viewed as a list rather than as a cons.”

The similarities between Prolog and Erlang are to be expected, of course, given Erlang’s history as starting out as a hacked up concurrent Prolog.

It’s the lack of the notion of a function that returns something that makes my implementation look so yuck. It’s pretty much a straight-up translation of the Erlang version.

And Danie, kudos for the clever insight! I spent too long thinking how to do the obvious and tedious iterate-over-list way of summing before realising how your Haskell implementation worked.

Thanks for the Prolog, interesting to see the similarities with Erlang.

My Lisp attempt used cdr where your’s used rest (like Clojure). Cool, I thought Common Lisp was stuck with the cryptic cdr.

(defun pairwise-add (l)
(mapcar #’+ l (rest l)))

I had tried to solve the problem with a fold, before I realised (upon googling zipWith) that I was using the wrong hammer!

Also, please someone improve this Prolog version:

sumpairs([X,Y|T],Out) :- Z is X + Y, sumpairs([Y|T], Tail), append([Z],Tail,Out).
sumpairs(_,[]).

(Yes, I did rampantly steal Danie’s very clever solutions.)

I like the Haskell solution!
It is just as elegant as the Clojure example, and probably much faster.

The Perl solution above returns [3, 7, 11, 15, 9] when I execute it.

According to my calculations it should rather return
[3, 5, 7, 9, 11, 13, 15, 17]

(on an array from 1 to 9)

zipWith (+) x (tail x)

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my @array = (1, 2, 3, 4, 5, 6, 7, 8, 9);
push @array, 0 if scalar @array % 2;
my %hash = @array;
my @sum = map { $hash{$_}+$_ } sort keys %hash;

print Dumper(\@sum);