| --- Log opened Thu Jul 21 00:00:45 2016 |
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| --- Log closed Thu Jul 21 07:49:16 2016 |
| --- Log opened Thu Jul 21 07:56:34 2016 |
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| 11:19 | <@TheWatcher> | I fucking hate Jenkins. |
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| 11:57 | < catadroid> | ...too much of my self confidence is wrapped up in knowing irrelevant minutiae about C++ |
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| 18:47 | <@Alek> | gah, closures are making my head hurt. |
| 18:48 | <@Alek> | function multiplier(factor) { |
| 18:48 | <@Alek> | return function(number) { |
| 18:48 | <@Alek> | return number * factor; |
| 18:48 | <@Alek> | }; |
| 18:48 | <@Alek> | } |
| 18:48 | <@Alek> | var twice = multiplier(2); |
| 18:48 | <@Alek> | console.log(twice(5)); |
| 18:50 | <&[R]> | Seems like you're understanding them fine there. |
| 18:53 | <@abudhabi> | [R]: You can totally use something without understanding it. |
| 18:54 | <@abudhabi> | Alek: Which part is hand to understand? |
| 19:00 | <@ErikMesoy> | A monad is a first-class monoid in the category of endofunctors, what's so hard to understand? |
| 19:00 | <@Tamber> | Uh-huh. Yup. Some of those are words. |
| 19:01 | <@abudhabi> | Alek: "multiplier" is a function. In JS, you can treat functions sort of like objects - this includes making sort of instances of them. |
| 19:02 | <@abudhabi> | Alek: Here, you are creating an instance of the "multiplier" function with a specified argument, and calling it "twice". |
| 19:03 | <@abudhabi> | Alek: Then you are calling "twice" with an argument too. Those two are multiplied, and you get 10. |
| 19:03 | <@abudhabi> | Alek: There is a trick here that multiplier returns a function of its own. That's how you get two arguments not overwriting each other. |
| 19:04 | <&McMartin> | This is also a simpler example, because the objects closed over (aka "captures", aka "upvalues", depending on who's writing about them) are immutable |
| 19:04 | <@abudhabi> | Alek: The "factor" argument gets assigned the first time, and is then baked into the instance. |
| 19:06 | < catalyst> | A monad is an abstraction Haskell programmers can use to kid themselves that their language has real world usages |
| 19:06 | <@Tamber> | XD |
| 19:06 | < catalyst> | The class is an abstraction that allows programmers with no class to get work done |
| 19:06 | <@ErikMesoy> | Alek: Maybe it helps to try to mentally disentangle the bits of what's going on. Draw a blackbox around the inner part. |
| 19:06 | <@ErikMesoy> | function multiplier(factor) { return blackbox } |
| 19:07 | <&[R]> | That won't work, since factor is no longer in the scope. |
| 19:07 | <@ErikMesoy> | I said "mentally". |
| 19:07 | <@ErikMesoy> | This is not actual code. |
| 19:08 | <&McMartin> | I think R is objecting because it's very hard to blackbox the act of closure creation. |
| 19:09 | <@ErikMesoy> | You give "2" to Multiplier, and Multiplier does something with the 2 and hands back a 2-related black box. Now you can give "5" to the black box, and the black box does something inside and gives back a 10. |
| 19:09 | <&McMartin> | That said, yes, if Alek's pain point is not closures per se but actually function literals, then this is where we need to be |
| 19:17 | < ToxicFrog> | Mmmm, closures |
| 19:17 | <&McMartin> | Also, since IIRC Alek hasn't actually done work with classical OOP languages my glib transformation of closures to and from OOP objects won't help. :( |
| 19:18 | <&McMartin> | On the plus side, JS's implementation of closures is by a wide margin the finest aspect of the language, and it is exactly as suitable for teaching them as Scheme. |
| 19:18 | <&McMartin> | The sharp edges surrounding it have to do with other weirdness and not the implementation of closures themselves. |
| 19:19 | <&McMartin> | (And that sharp edge is filed off, sort of, in ES6, though the syntax is subtle enough that I do wonder how much sense it will make to someone who didn't already use Lisp) |
| 19:46 | < catalyst> | (It's almost like Eich wanted to implement Scheme in the browser) |
| 20:08 | <@Alek> | R, I was copy pasting from the book. -_- |
| 20:09 | <@Alek> | what I didn't get was how the number came from outside to the inside. something to do with the return function() thing? |
| 20:09 | <&[R]> | The inner function retains its scope |
| 20:10 | <@Alek> | ah, it returns a second function, got it. that helps. also, getting a bit of rest away from the book helped. |
| 20:10 | <&[R]> | Yeah, it took me a while to realize that myself |
| 20:11 | <&[R]> | Also, the semi-colons are superfluous. Especially the one after the } |
| 20:11 | <&[R]> | That one bothers me |
| 20:11 | | * Alek points at the book. -_- |
| 20:11 | <&[R]> | I know |
| 20:12 | <@Alek> | how would it work without assigning multiplier() to a var first? would it even work at all? |
| 20:13 | <&[R]> | multiplier(2)(5) |
| 20:13 | <@Alek> | O_O |
| 20:13 | <@Alek> | well, that's a thing. |
| 20:13 | <&[R]> | Though that looks silly and is slightly confusing. |
| 20:14 | <&[R]> | Also obviously you can pass it to a function expecting a callback |
| 20:14 | <@Alek> | callbacks, that's another thing yet to learn. |
| 20:15 | <&[R]> | Callbacks are basically just functions you pass to another function, it's how JS can do async code. |
| 20:15 | <&[R]> | eg: file.on('data', function(data) { /* do work with data */ }) |
| 20:17 | <@Alek> | hmm |
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| 20:18 | <@Alek> | "Almost any program can be made faster by making it bigger and more convoluted." ahahaha |
| 20:18 | <@ion> | O_o |
| 20:18 | <&[R]> | Are you doing a project as you learn JS? |
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| 20:18 | <@Alek> | not yet. |
| 20:18 | <&[R]> | lolwut |
| 20:18 | <@ion> | that's a somehow disturbing sentence |
| 20:18 | <&[R]> | What book are you reading? |
| 20:18 | <@ion> | Also yeah, I was about to ask what book |
| 20:18 | <@Alek> | the only environment the book offers is the in-page sandboxes. |
| 20:18 | <&[R]> | Also, MDN is pretty much /the/ JS reference. |
| 20:18 | <@Alek> | Eloquent Javascript |
| 20:19 | <@Alek> | and I wouldn't have any idea what kind of project to go with, much less environment. |
| 20:19 | <&[R]> | Never heard of it. |
| 20:19 | <@Alek> | http://eloquentjavascript.net/ |
| 20:20 | <&[R]> | https://github.com/marijnh/Eloquent-JavaScript <-- supposedly all the code samples are there |
| 20:21 | <&[R]> | Oh wow, it's actually the whole book |
| 20:21 | <@ion> | Haha, I love this trend of publishing books in public repos like github |
| 20:21 | <@Alek> | the website I gave is the whole book. with code samples in inline sandboxes. |
| 20:21 | <@Alek> | that I can edit and run. |
| 20:22 | <@ion> | also I'm not much of a coder, but that seems like a horrifically javascript-happy comment to make, if your quote about faster more convoluted programs is from there. |
| 20:23 | <@ion> | it'd certainly explain a lot of webpages I visit, if that's the sort of advice being given to javascript developers anyhow... |
| 20:26 | <@Alek> | wow. the +5 || *3 return recurse is something, that's for sure. |
| 20:26 | <@Alek> | yeah, it's from the book. needs a bit of context though, since it's from the recursive functions section. |
| 20:28 | <@Alek> | the book gives sample code of using function recursion to find powers from a number and an exponent, mentions a prior sample using loops instead, says the recursive code is simpler and more elegant (and shorter?), and then mentions it takes longer to run. |
| 20:30 | <&McMartin> | Suffice to say that the short form there there kind of has it backwards |
| 20:30 | <&McMartin> | It's more "optimizing for performance damages readability and maintainability, which is why you do it last and only when you can prove you need to" |
| 20:30 | <&McMartin> | The claim that a recursive solution is cleaner and simpler than an iterative solution is... a claim to evaluate on a case-by-case basis. |
| 20:31 | <&McMartin> | For an example from my current project, say I want to split 1+2+3+4 into a set of three individual additions of two terms. |
| 20:32 | <&McMartin> | If I want to group them (1+(2+(3+4))), then it turns out recursion is much simpler |
| 20:32 | <&McMartin> | But if I want to group them(((1+2)+3)+4) then iteration is actually just as clean. |
| 20:32 | <&McMartin> | Know both techniques; you'll eventually pick up a feel for it. |
| 20:33 | <&McMartin> | (They can be transformed into one another mechanically, but the results of that are pretty much always ugly.) |
| 20:33 | <~Vornicus> | (the way most systems work is the latter |
| 20:34 | <&McMartin> | Right, and if you shift focus over to the functional languages, they usually have functions with names you can read as "fold left" and "fold right", which is the general case of my example above. |
| 20:34 | <&McMartin> | Fold Right pretty much has to be recursive, Fold Left can be iterative. |
| 20:34 | <&McMartin> | (Fold Right is the kind of problem where if you do it with a loop, you end up implementing your own version of function call semantics by hand, so you really should just be making function calls.) |
| 20:37 | <~Vornicus> | (clearly, reverse it, then foldl :P) |
| 20:37 | <~Vornicus> | (don't do it that way) |
| 20:37 | | * ErikMesoy mutters dark curses on "optimize for performance" |
| 20:37 | <&McMartin> | (Doesn't preserve results) |
| 20:38 | <&McMartin> | ErikMesoy: You say that, but then you have people who perform SQL queries that return 50,000 rows of which they read one, and say "well, premature optimization is the root of all evil! :shrug:" |
| 20:39 | <@ErikMesoy> | McMartin: Yeah, and people doing O(n^3) calls that could be done in O(n). |
| 20:39 | <@ErikMesoy> | I know about it in theory. But in practice I mostly seem to encounter stuff that doesn't so much need "optimization" as "you're doing it wrong, stop doing it wrong". |
| 20:40 | <&McMartin> | The polite term for that is "algorithmic optimization" |
| 20:40 | <&McMartin> | But yeah, that goes way back, too. If the slow one is simpler or smaller people will go for it if it's good enough for the initial use case. |
| 20:40 | <@ErikMesoy> | "optimization" I associate with things more like going from (n^2) to (n log n). |
| 20:40 | <&McMartin> | Yes, exactly that |
| 20:41 | <&McMartin> | A bunch of old 8-bit European videogames actually used bubble sort to scene-sort their sprite displays, because that was fast enough to do once a frame at 50Hz |
| 20:41 | <&McMartin> | People cracking it for the North American scene had to rewrite the rendering code to use an n log n sort instead to retain a stable 60Hz display |
| 20:41 | <&McMartin> | Even so I can't say the first guys were "doing it wrong". |
| 20:42 | <&McMartin> | There's also issues like "how big does N get" |
| 20:42 | <&McMartin> | If N is never going to be above, like, 6, you're probably good to go for O(2^N). |
| 20:43 | <&McMartin> | I'm pretty comfortable saying "if you're in a world where low-level performance tuning matters, you shouldn't be writing in a scripting language" |
| 20:44 | <@ErikMesoy> | Corollary: Seeing as I'm writing in a scripting language, I shouldn't do anything where performance tuning matters? |
| 20:44 | <&McMartin> | There's an amazing book that's a retrospective on assembly language programming the x86 from the Pentium back to the 8088, by a guy who did engine work for both iD and MS |
| 20:45 | <&McMartin> | He hammers your point here hard, and includes the fantastic line "There is nothing more sad than fast slow code" |
| 20:45 | <&McMartin> | (By which he means hyper-optimized bubble sorts and such) |
| 20:45 | <&McMartin> | ErikMesoy: If you gotta, I'd say go the classic Python route of "use the script for glue and logic, use the best algorithms there, have them coordinate operations implemented in a systems language" |
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| 20:46 | <&McMartin> | Even in Python you might find something like "oh hey, using a sorted set instead of an unsorted one alters performance by X% because of our specific workload" or whatnot |
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| 20:46 | <&McMartin> | Those don't hurt |
| 20:46 | <&McMartin> | But you should probably leave a memo to your future self about why you're doing something that looks weird |
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| 21:51 | <&jeroud> | If you want fast Python code, use pypy. |
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| 22:46 | <@Alek> | just don't let anyone else play with your pypy. |
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| 22:48 | <&McMartin> | Incidentally, the "amazing book" I mentioned earlier is also available online, albeit as a PDF |
| 22:48 | <&McMartin> | http://www.drdobbs.com/parallel/graphics-programming-black-book/184404919 |
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| --- Log closed Fri Jul 22 00:00:01 2016 |