Talk:Monad (functional programming)

This is actually the same as Monad (category theory). These should be merged. —Ashley Y 22:19, 2004 May 31 (UTC)

They're not really the same thing: an explanation of Haskell's IO monad doesn't belong in an article on category theory, and a detailed explanation of monads in category theory isn't relavent to the average Haskell programmer. In addition, many standard Haskell monads aren't strictly speaking monads at all. I think it's probably best to keep the articles separate. Cadr 22:28, 31 May 2004 (UTC)Reply

Which Haskell monads are not monads in the CT sense? —Ashley Y 09:58, 2004 Jun 1 (UTC)

The IO monad is one example (see [1]). Cadr 11:08, 1 Jun 2004 (UTC)

It's not clear, actually, since the difference is only visible with the 'seq' function, which is considered slightly dubious anyway. More importantly, these are Haskell's monad laws that IO may or may not be properly living up to: the sense in which "monad" is used in Haskell is precisely the CT sense.

If you think this should be a separate article, rename it "Monads in functional programming", rather than the () notation which suggests that it's a separate sense of the word.—Ashley Y 02:49, 2004 Jun 2 (UTC)

OK, but it's still the case that the two articles cover very different information. I'm fine with it being renamed to Monads in functional programming. Cadr 14:15, 2 Jun 2004 (UTC)

Rename (from "Monad (functional programming)") done. —Ashley Y 23:27, 2004 Jun 2 (UTC)

Er, the first sentence of the second para (and possibly more) looks like a copyvio from http://nomaware.com/monads/html/introduction.html#what --- I don't know the topic well enough to rephrase to eliminate this. Could someone who knows the topic look into this? thanks, jdb ❋ 06:00, 27 Jan 2005 (UTC)

par function

Latest comment: 19 years ago6 comments4 people in discussion

Why is the function ${\displaystyle (x,y)\mapsto {\frac {1}{{\frac {1}{x}}+{\frac {1}{y}}}}}$  called par? --MarSch 11:06, 25 October 2005 (UTC)Reply

At least that's the function for total resistance of two resistors in parallel coupling. --TuukkaH 16:14, 25 October 2005 (UTC)Reply

For people used to reading C++ all day, "//" is a very difficult operator name to read. It looks like the start of a comment, and it's almost painful to have to ignore such "comments". Perhaps it could be renamed to "./." or even "///"? Kimbly 02:52, 10 January 2006 (UTC)Reply

What about "::", "->", and "--"? (and "|", ">>=", ">>" and "++", further down the page.) Like "//", they all have specific, and entirely different, meanings in C++. Beyond C++ and Haskell, you'll find yet other meanings for them. What makes C++'s "//" special enough to avoid?

Besides, it's fairly clear that the examples are not in C++, so i don't see how it could cause more than momentary confusion, at worst. --Piet Delport 04:34, 10 January 2006 (UTC)Reply

In most grammars, comment signs are special: // and /* in C++, Java etc., # in Python etc., ; in Lisp, -- and {- in Haskell. I noticed I've special-cased them too and skip text in them automatically. C++ programmers are used to << etc. meaning many things because they are overloaded already in the standard and most every language has operator overloading. Of course you can get accustomed to any a syntax, but do we want to make it as hard as possible for people to read this article? It's not like // would be an integral part of the Haskell syntax. --TuukkaH 09:19, 10 January 2006 (UTC)Reply

I know what you mean, I've had the same problem with people using # or ## as an operator, while in Python, shell etc. they are used to start comments. As this page isn't strictly about Haskell, if we want to use Haskell as an example, we could still try to remove unnecessary readability problems from the article. --TuukkaH 05:50, 10 January 2006 (UTC)Reply

Rewrite

Latest comment: 19 years ago1 comment1 person in discussion

I guess my scam is up. I haven't really used Haskell any significant amount, and I barely understand this monad stuff. I just hoped I might be able to push this article away from the two mistakes so many monad tutorials make—presenting them as "how you do I/O" or completely neglecting to give any intuition to the general concept of a monad. I did my rewrite with a copy of Wadler's "Comprehending Monads" in hand, but since I made so many mistakes I'll tag the article for verification. TuukaH is correct above about the naming of par. Gazpacho 04:13, 29 October 2005 (UTC)Reply

Haskell

Latest comment: 19 years ago2 comments2 people in discussion

This page really seems to be more about monads in Haskell, rather than in a generic programming language. The examples given seem to be in Haskell, which for non haskell programmers (i.e. me) are really hard to follow.

Shouldn't this either be renamed to something like "Monads in Haskell" with a link to understanding Haskell, or have the equations written in a common mathematical way?

If I understand correctly, monads are containers for values: for example, a monad value like "Just 5" contains the value 5. The return function "wraps" a value inside a monad, the fmap function allows another function to "look inside" a monad value, and it looks like join turns a value like Just (Just 5) into Just 5, or [[3]] into [3]. A few examples:

return 3 = either [3] or Just 3 -- "Wrap" the value 3 with a monad
fmap (+1) [3,2,4] = [4,3,5] -- (+1) is the incrementor function, and it is allowed to "peek inside" this list to increment everything inside it.
fmap (+1) (Just 5) = Just 6 -- Peeking inside a "Just" value.
join Maybe (Maybe 7) = Maybe 7 -- "Joining" these two Maybe's into one
join [[2]] = [2] -- Joining a listifier with a listifier

Is this clear enough? --67.172.99.160 02:09, 3 December 2005 (UTC)Reply

Kind of. Monads are types with associated functions (bind (written >>=) and return). These are sometimes containers in a naive way — the List monad and Maybe monad. But monads like CPS "contain" something, but it's not directly accessible in any way. More complicated monads do even crazier things: threaded coroutines can be expressed as a monad. Taking an example from a tutorial site (sorry, can't find the URL), a monad could keep a value corresponding to the remaining number of steps to allow in the computation; when this counter reaches zero, all binds just return the value computed up to that point. None of these are "containers for values" in any sensible way.

I don't think moving to "Monads in Haskell" is appropriate. It begins by describing everything abstractly, but eventually we need to discuss monads in practice. Our choices are limited to Haskell, Clean, and Miranda^TM. Every other programming page just picks a language, so why not here? If another language you know of uses monads in an interesting way and with a different syntax, by all means add it in!

I think the current explanation is fine. In that sense the "cite" tag is inappropriate, but it would be nice to cite some source on monads anyway. --Mgreenbe 10:00, 4 January 2006 (UTC)Reply