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I appreciate these attempts to give non-Haskellers a chance to learn Monads but, personally, I never really grokked them until I got into Haskell. In Haskell, M

I appreciate these attempts to give non-Haskellers a chance to learn Monads but, personally, I never really grokked them until I got into Haskell. In Haskell, Monads are defined in terms of types, thus languages without type systems like Haskell's make the concept both more difficult to understand and less (immediately) useful. Having been through many of these tutorials myself, I think the best way to get into Monads (as well as many other useful constructs like Functors, Monoids and Monad Transformers) is to roll up your sleeves and learn Haskell (Learn You A Haskell is a great and relatively quick read). As a bonus, you'll also learn one of the most elegant programming languages around. This comment isn't intended as a knock against the article. I think there's a lot of merit in using monadic constructs in languages that aren't Haskell, I just think Haskell's type system makes understanding the concept easier.

sbochins 14y ago
I don't really have the experience to comment on this issue, but I did try looking at another monad tutorial in Clojure several months ago. I think I kind of got the idea behind monads, but I always thought so what. I have no experience with Haskell. I supposed that may be the reason.
swannodette 14y ago
I disagree. The only sensible introductory text I've found about them is for Scheme - http://www.cs.indiana.edu/~cswords/monads.pdf http://www.cs.indiana.edu/~cswords/monads.pdf. Folks love to emphasize the types - but how one might implement them matters just as much if not more IMO. Also, I've found the usage of monads as the building blocks for modular interpreters to shed the most light on their power, utility, and limitations (see the various papers from Steele, Wadler et al, Hudak et al, and Felleisen et al).
- monkeyfacebag 14y ago
  > but how one might implement them matters just as much if not more IMO This is a false choice. Learning monads through Haskell, you get the forest and the trees! That said, I get that there are legitimate differences of opinion and what worked for me will not necessarily work for others. I feel like some understanding of types (or categories, etc.) is necessary to fully grok monads. Both this article and your linked paper offer some basic explanation of the concept. Tutorials that are essentially implementations of bind are, in fact, missing the forest for the trees.
- cageface 14y ago
  Really your choice for an introduction to monads puts this in an intro paragraph? Before we begin, it is important to brieﬂy talk about the λ- calculus in the context of termination. In short, the λ-calculus is strongly normalizing and thus non-termination is impossible as a general rule.
breckinloggins 14y ago
I think it's a "to each his own" thing. Personally I've always found Haskell's syntax to be distracting. The operators are kind of visually "thick" and the prefix/postfix/infix mix obscures the logic for me. Of course, this is because I only barely grok Haskell. If I really knew Haskell I'm sure I wouldn't have an issue with the syntax, but as someone trying to learn about Monads from a category-theoretic perspective, Haskell just ends up confusing me more than the extra annotations provided by its type system can compensate. I found I understood monads a little better after this article, because the Lisp syntax is uniform enough that it disappeared into the background. The lack of type annotation brings some fresh confusion right back in, but that's the cost of using Clojure for this example. Again, all of this is just how my own brain works. Your brain may vary :) An interesting approach would be to try teaching monads with typed Racket. [1] [1] http://docs.racket-lang.org/ts-guide/ http://docs.racket-lang.org/ts-guide/
- tikhonj 14y ago
  If you're coming from a mathematical perspective (I should note that I didn't but kind of wish I did), then the Haskell type system has an additional advantage: it's very obvious how Haskell types form a category and I've found it's very easy to visualize how functors, monads and so on "look" (for lack of a better term) on the category of Haskell types. Of course, I'm really trying to do the opposite--get a basic understanding of the math from using functors, monads and so on in Haskell. I also read about type theory for fun, so maybe I'm not the least biased person to ask about static typing :P.
chrismsnz 14y ago
I've been spending some time to try and pick up Haskell and I just thought I'd mention that I found "Real World Haskell"[0] to be a bit more understandable and accessible to me than "Learn you a Haskell". Different strokes, obviously, but just thought I'd mention an alternative. [0]: http://book.realworldhaskell.org/ http://book.realworldhaskell.org/

sbochins 14y ago

I don't really have the experience to comment on this issue, but I did try looking at another monad tutorial in Clojure several months ago. I think I kind of got the idea behind monads, but I always thought so what. I have no experience with Haskell. I supposed that may be the reason.

swannodette 14y ago

I disagree. The only sensible introductory text I've found about them is for Scheme - http://www.cs.indiana.edu/~cswords/monads.pdf http://www.cs.indiana.edu/~cswords/monads.pdf. Folks love to emphasize the types - but how one might implement them matters just as much if not more IMO. Also, I've found the usage of monads as the building blocks for modular interpreters to shed the most light on their power, utility, and limitations (see the various papers from Steele, Wadler et al, Hudak et al, and Felleisen et al).

monkeyfacebag 14y ago
> but how one might implement them matters just as much if not more IMO This is a false choice. Learning monads through Haskell, you get the forest and the trees! That said, I get that there are legitimate differences of opinion and what worked for me will not necessarily work for others. I feel like some understanding of types (or categories, etc.) is necessary to fully grok monads. Both this article and your linked paper offer some basic explanation of the concept. Tutorials that are essentially implementations of bind are, in fact, missing the forest for the trees.
cageface 14y ago
Really your choice for an introduction to monads puts this in an intro paragraph? Before we begin, it is important to brieﬂy talk about the λ- calculus in the context of termination. In short, the λ-calculus is strongly normalizing and thus non-termination is impossible as a general rule.

breckinloggins 14y ago

I think it's a "to each his own" thing. Personally I've always found Haskell's syntax to be distracting. The operators are kind of visually "thick" and the prefix/postfix/infix mix obscures the logic for me. Of course, this is because I only barely grok Haskell. If I really knew Haskell I'm sure I wouldn't have an issue with the syntax, but as someone trying to learn about Monads from a category-theoretic perspective, Haskell just ends up confusing me more than the extra annotations provided by its type system can compensate. I found I understood monads a little better after this article, because the Lisp syntax is uniform enough that it disappeared into the background. The lack of type annotation brings some fresh confusion right back in, but that's the cost of using Clojure for this example. Again, all of this is just how my own brain works. Your brain may vary :) An interesting approach would be to try teaching monads with typed Racket. [1] [1] http://docs.racket-lang.org/ts-guide/ http://docs.racket-lang.org/ts-guide/

tikhonj 14y ago
If you're coming from a mathematical perspective (I should note that I didn't but kind of wish I did), then the Haskell type system has an additional advantage: it's very obvious how Haskell types form a category and I've found it's very easy to visualize how functors, monads and so on "look" (for lack of a better term) on the category of Haskell types. Of course, I'm really trying to do the opposite--get a basic understanding of the math from using functors, monads and so on in Haskell. I also read about type theory for fun, so maybe I'm not the least biased person to ask about static typing :P.

chrismsnz 14y ago

I've been spending some time to try and pick up Haskell and I just thought I'd mention that I found "Real World Haskell"[0] to be a bit more understandable and accessible to me than "Learn you a Haskell". Different strokes, obviously, but just thought I'd mention an alternative. [0]: http://book.realworldhaskell.org/ http://book.realworldhaskell.org/