What do we call this (new?) higher-order function?

Question

I am trying to name what I think is a new idea for a higher-order function. To the important part, here is the code in Python and Haskell to demonstrate the concept, which will

Answer 1

In Python the meld equivalent is in the itertools receipes and called pairwise.

from itertools import starmap, izp, tee

def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = tee(iterable)
    next(b, None)
    return izip(a, b)

So I would call it:

def pairwith(func, seq):
    return starmap(func, pairwise(seq))

I think this makes sense because when you call it with the identity function, it simply returns pairs.

Answer 2

So because there seems to be no name for this I suggest 'merger' or simple 'merge' because you are merging adjacent values together.

So merge is already taken so I now suggest 'meld' (or 'merger' still but that may be too close to 'merge')

For example:

meld :: (a -> a -> b) -> [a] -> [b]
meld _ [] = []
meld f xs = zipWith f (init xs) (tail xs)

Which can be used as:

> meld (+) [1..10]
[3,5,7,9,11,13,15,17,19]
> meld compare "hello world"
[GT,LT,EQ,LT,GT,LT,GT,LT,GT,GT]

Where the second example makes no real sense but makes a cool example.

Answer 3

this seems like ruby's each_cons

ruby-1.9.2-p0 > (1..10).each_cons(2).to_a

=> [[1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9], [9, 10]] 

Answer 4

Nice idiom! I just needed to use this in Perl to determine the time between sequential events. Here's what I ended up with.

sub pinch(&@) {
  my ( $f, @list ) = @_;
  no strict "refs";

  use vars qw( $a $b );

  my $caller = caller;
  local( *{$caller . "::a"} ) = \my $a;
  local( *{$caller . "::b"} ) = \my $b;

  my @res;
  for ( my $i = 0; $i < @list - 1; ++$i ) {
    $a = $list[$i];
    $b = $list[$i + 1];
    push( @res, $f->() );
  }
  wantarray ? @res : \@res;
}

print join( ",", pinch { $b - $a } qw( 1 2 3 4 5 6 7 ) ), $/;
# ==> 1,1,1,1,1,1

The implementation could probably be prettier if I'd made it dependent on List::Util, but... meh!