daniel gratzer

I suppose that's almost the "Haskell zen"

link

@JimmyHoffa It's essentially a generalization over foldr and unfoldr, it's got mathy names (cata, ana, ..) but it's not terrible

@JimmyHoffa Have you looked at recursion-schemes yet? I've been having a lot of fun with it for the last 2 weeks :D

@MichaelT I see what your saying.. yeah I might do that, I can't fit all my books in my dorm :(

@ratchetfreak I'm fairly certain in my little suburb they'd send in riot police :P

Trying to figure out how to move all my crap... it's going to be an adventure

@JimmyHoffa CMU actually :) (I got into both, ended up choosing cmu) and yep!

Hi all

Also Hi Everybody

@JimmyHoffa Yep, I lived about 3 blocks away from that square over the summer.

Everything is seg-faulting D:

I heard monad and OCaml

Hi all

@WorldEngineer More Self, though it is one a few dynamic languages with mostly working closures which is nice :)

Oh god help me, I'm starting to enjoy some javascript

@JimmyHoffa Did my rant above make much sense? I was somewhat asleep when I wrote it :$

btw I do believe Foldable is the relevant typeclass here

This is clearly not the case for all functors so not all functors give rise to a catamorphism

So essentially, a cata exists whenever the F-algebra F a -> a exists

this is normally called cata.

hom :: Functor f => Alg f a -> Fix f -> f a
hom alg = fmap elim . unfix
    where elim = alg . fmap elim . unfix

Sorry, between the carriers of alg and initAlg which are f a and Fix f respectively

Now using this, we need to prove that for every algebra alg :: Alg f a, there is a map between initAlg and alg

type Alg f a = f a -> a
initAlg :: Alg f (Fix f)
initAlg = Fix

In our case, we're interested in a specific initial algebra, which is given by

An initial algebra is one with a unique map to all algebras in the group we're considering. A catamorphism is the unique homomorphism from the initial F-algebra to all others.]

data Tree a = Leaf a | Branch (Tree a) (Tree a)

The classic example of a catamorphism comes from the functor

@JimmyHoffa I'm not so sure. A functor is simply a mapping yes, a catamorphism is meant to model a mapping from an initial algebra to any algebra in a category. A functor can give rise to an F-algebra, but need not necessarily. For example if IO give rise to an F-algebra unsafePerformIO is trivially derived.

Oddly enough the OP didn't care haha

Fair enough

Thanks for mentioning it though :)

@GlenH7 Fair enough, yeah it didn't realize it would upset that many people :$

@JimmyHoffa To my understanding it seems that they actually do prefer lists. Seqs are lists :) So map filter etc are all operating on lists, it's just htat if you're doing access by index or whatever, vector is way more efficient

@YannisRizos So automating is probably just redundant then.

Seems fair, trolls are annoying/distracting

@YannisRizos And at that point I can't imagine the community hasn't notified you with some form of "stop trolling".

@YannisRizos Is there a consequence after a certian number of flags? Like "comment banning" or something? Because if so I'd definitely want to know that I'm being annoying before being banned/punished

@YannisRizos Oh alright, that's what I was hoping for. Ignore me :)

@Ampt hmm fair, I just thought of that.. though there's the same risk with closed/deleted questions and that doesn't happen too much

RFC, deleted comments should notify the poster? My comment got deleted (probably fairly, sorry about that) but I wouldn't know about it if I didn't go back to delete it myself..

@JimmyHoffa yeah :( I'm particularly sad when it's PHP as their blub.. trying to argue with PHP fanatics makes me sad on the inside

Yeah.. I'd expect that more in Scala than clojure htough

Lisps have never really been gung-ho on ADTs

@JimmyHoffa Possible, I suspect that the clojure community is in two camps. "Java with lambda + macros" and "Common lisp/Scheme with Java access"

@JimmyHoffa Fun, suggestion, Hoogle type app for clojure? Based on your question it could come in handy

@JimmyHoffa Learning Clojure?