Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

Re: RFC: Should join subsume reduce?

by nothingmuch (Priest)
on Feb 24, 2006 at 00:49 UTC ( #532433=note: print w/replies, xml ) Need Help??

in reply to RFC: Should join subsume reduce?

reduce is also known fold, and foldr and foldl can be used to implement any of grep, map, join, sum, etc etc etc.

In Haskell Perl's join can be reimplemented as this:

join _ [] = [] -- this means that join on the empty list is the empty +string join delim strings = foldl1 (\left right -> left ++ delim ++ right ) s +trings -- this is join implemented with reduce -- also this could be written as join delim strings = foldl1 ((++) . (++ delim)) strings -- or more perlishly join delim strings = foldl1 (\left right -> concat [left, delim, right +]) strings -- or with autocurrying fun join = foldl1 . ((++) .) . flip (++)
And and similarly we can implement this with List::Util's reduce very elegantly too:
sub join { my ( $delim, @strings ) = @_; reduce { $a . $delim . $b } @strings; } but in this case the concatenation operator is not used directly as th +e a curried higher order function
A tutorial on the universality and expressiveness of fold is a wonderful article on this topic. There are some diagrams to assist you in understanding the article, too.

Since you seemed to like to reference, see The Wheel Gets Reinvented.

Lastly, the argument that adding reduce to Perl will break code is wrong - err, lock and others were added post factum as weak keywords - keywords that are only available if there is no sub by that name in the current package already.

zz zZ Z Z #!perl

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://532433]
[marto]: Eily, there's actually a lot of good discussion on the topic in the HN link choroba posted
[marto]: sorry for the late response, busy busy :/
[Corion]: I think you need to load Readline in the debugger, but I don't know how
[Corion]: Yay, invitation for a team-building workshop, with a team of 100 people :-/
[Eily]: marto after an additional read I started to see the light actually. And choroba's link was helpful as well :)
[Corion]: I'll send my colleague who doesn't yet know the people there, and I'll do production duty instead.

How do I use this? | Other CB clients
Other Users?
Others studying the Monastery: (10)
As of 2017-07-26 15:01 GMT
Find Nodes?
    Voting Booth?
    I came, I saw, I ...

    Results (396 votes). Check out past polls.