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Scala.js and WebAssembly, a tale of the dangers of the sea
Sébastien Doeraene, Executive director of the Scala Center
Thursday, June 13, 2019 · 11:18 a.m. · 50m 41s
Scala.js compiles to JavaScript with two major goals in mind: interoperability with JavaScript libraries, and portability with respect to Scala/JVM. With the rise of WebAssembly as an alternative to JavaScript in the browser, one cannot help but wonder whether we could compile Scala.js to WebAssembly, with the promise of better performance. Unfortunately, WebAssembly quickly appears as a siren, and the path to it navigates between Charybdis and Scylla, the threats to interoperability and portability. Come and explore the sea with us, and meet its dangers. Required Knowledge: We assume that the audience has a strong working knowledge of Scala, is at least somewhat familiar with JavaScript, and can read at least one assembly-like language. Knowledge of WebAssembly itself or compilers is not necessary.
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so um let's start first session on aunts colleges in web assembly
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a tale of the dangers of the c. when i submitted talk effect like being very poetic
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um and and then when you actually get to prepare the talk in the technical
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details and then suddenly read as maybe i was not a good idea um thing
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so um but anyway are otherwise will will of course take to due to the
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content but you might not see as many images of carry this insecurity might have wanted
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also for one eng harming there won't be any demo and
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this talk another what i'm going to talk about works um
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so if you wanted to uh see something that works hard
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you still have time to run to one of the other talks you wanted to see
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um so this is completely purely to radical uh if you
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were ads i'm kelly stock just before she was talking about
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talked driven development uh when she submits the talk and then
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she learns or implements the things she's she was to talk
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about that was kind of the idea of that stuff um i did with this topic that they didn't get to actually
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take the time to uh implement any of this so this
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is all dirty theoretical but hopefully it will still be interesting
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okay let me start by i'm asking ah as
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is is more question um basically like think about
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for you what what is coloured is like is it is the compactor is the macro is the
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language is that just a library um is this
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side project uh and or or is it an ecosystem
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and i want to assure transfixed complicated take teaching too
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much time and i haven't prepared nice a nice online
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polls like like keynote so let me just answer the question for you um to it as a competitor him
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it is also when you insist him and for that i'm super glad that it's uh people
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in the community actually like build ever isn't our it's uh it because otherwise it wouldn't be useful
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uh but most importantly for the purpose of this talk it is eighty language
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so i probably menu you taught it's colour with the language and storage areas
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is like the same language so why why is it really language
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well 'cause it's actually brunettes really distinct from scholar the v. m.
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i i'm very proud of always talking about how portable it is and how you can take
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any any library and just change to build and
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then suddenly it also compiles for the java platform
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but the real a a as a other also a few
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things that make it's quite distinct from psychology um as a language
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you might have heard of undefined behaviours um there was a talk yesterday
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that said if you access and every other bounce it will just dues stuff
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on instead of reliably throwing an array index audubon exception or something like
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that to to to string call the primitive values is not quite the same
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on the test typist as well but the other details in the grand scheme of things and especially um
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for today what is relevant yeah is there is no java in syrup
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of course but there is javascript interrupt and that actually a big part of what's
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coverages as a language is you can't
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just late compiles colour javascript and and corridor
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they that's the easy parts ah m. fantasy easy i i truly mean it i
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did that in two weeks so you think and then it took me six years
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to get to where we are now so i'll so
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javascript interrupt is really this all of its colour g. s.
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and it's more it then just um what people
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would call f. f. five so foreign function interface
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it's really bi directional uh in trouble
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in the with objects function values states
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um properties and methods all of that you
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can call javascript sayings jostle can call you
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uh in synchronous way in asynchronous ways using call
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backs using futures in promises all of that stuff
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so you you have an example code that makes isn't match um
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to the maximum a manage to do in six lines of code
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java scripts and ends got um so you have to go to classes like points
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which is even the case class and states which is a which inside contains so um
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a reference to javascript array and that javascript array
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contains itself points which are against all our constructs
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and then you clean call the uh add events
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listener method from javascript and given the land uh
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and that land that is defined in this colour codes but it ends up being a javascript function
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that holds in its captures this got lost eights and then it mute
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it's that thing and so basically that you can do this sort of stuff
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we'll come back to this example in about thirty eight slides
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in the meantime ah let's go a lot of a talk a bit about
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what is what by someone and that you might have even less of an idea
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so if the compiler is the production machine is the the language the binary format
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is specific to the web i mean you might you might expect that isn't open standards
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so one is another compiler at all it's really a language a
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binary format and an open standard and it's not specific to the web
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and again most importantly for the purposes of this taught it is a language
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so it's might not be a language that you might want
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to write by hand at least not for more than ten
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or twenty lines of codes um so in fact the it's
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it's typically language that is the result of combining from another language
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so this is a bit with white ass oblique in look like it's on
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the left you have some ah c. plus plus code or or see or both
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i never remember the difference ah it's a factorial it's not a recursive i
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never write a recursive functions i don't know what people have with them um
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and on the right if you compile this way
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eighty um with the c. to web assembly compactor
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that is um very smart what you might
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yeah it's it's the results on the right
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um this is not actually what you will get with typical
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compares right no but it's the easiest code i could find
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no kind of fits the bill um so you can see that it's our it's basically just check
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machine so every instruction put something on the stack or pops things on the on the stack those computations
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um it looks like by codes birds um control
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flow is structured so instructions are all in there
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expressions or express on the stack but control flow like an if
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else is structured so there are blocks of if then else will will
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look more into details later about what what kind of things we can do what
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you can see there that we have our into sixty four years we have on some
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primitive operations like a sob multiplication we can call methods
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including um recursive really recursive calls and i kind of stuff
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oh so basically this is what you have in whereas only him you um you have
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a linear memory model so the kind of uh what you would get in in c. basically
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so basically the memory as one giant array of parts and you can
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have pointers into that array which are basically in this is into the array
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and there is absolutely no g. c. okay so this is what you get what works what doesn't right now
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so what i think we can sort of talk to javascript but in very limited ways and
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in in the way that i would in this case qualify as an for a function interface
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oh this is way too much codes for what you can see uh
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as i have on the left on a on javascript functions that i
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somehow give access to to javascript to web awesomely
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in whereas only i can imports those functions that this is the fourth line on the slides
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uh and then i can call them later on down down
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the line isn't additive text version of web assembly which is
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more like lisp um and the two versions are basically one
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to one correspondence is just a different way of expressing some
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intense that's that was just for the show are and also because it was the output of the compiler used um i
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didn't want to translate to the other form but they will stick to the other for for the rest of the talk
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um so here you can see that we have
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uh functions industry but take floaters parameters and return um
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sorry i probably get mixed up on the left of course you have some c. code um
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so it explodes it returns floats or avoid
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and that's about all you gets huh that's numbers and that's it
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so you have of i would also to really limited to you are
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passing thirty two bit integers to to within sixty four bit floats and that's it
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like little it is all the only thing you can like give
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between ah web s. and we and and and javascript so strings
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nope objects nope higher order functions
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definitely not he okay let's get two different light switches um
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let's try and compile psychologist to was um was it was a shortening of or by someone
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this is has got us works but and now you understand all astrology
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is basically uh you have a scale as sources you give them to
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discover compared to this gorgeous compared or it spits out some s. g.
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s. r. r. file i. r. files which stands for psychology as intermediate representation
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very large original and then uh i maybe put done maven or you pull
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other artifacts from a vendor contain those edges are false and you give them due
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to started to miser which message them spits out optimists i. r. and then
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there was a lasted that things that are are and outputs one big javascript file
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so if we want to compile psychologist web assembly we can
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re user sources hopeful that we can reuse is gorgeous combined or we can reuse
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the edges are for a files like all of that we can reuse gorgeous miser
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to a large extent some of the things it does are specific
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to optimising for javascript but would would just to activate those parts
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the one thing that we need to rewrite is the very last part which
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take the ultimate i. r. and in its web as somebody instead of transcripts
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so that means that i will show a lot of starches ironies
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talk because as our input format reality for what we're trying to do
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so to give you an idea what it looks like here is a fact
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or function again the non to records of one um but written in scar
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law about for scholarships to be precise and if you compile it would discourage
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us compare you end up with this i. r. which looks for is a matter
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uh what you see uh is that all method names have a mangled names
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of the overloading is i'll come by the way you have primitives like ins
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every operation is stacked with the type of appearance it takes like the
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equality compare isn't in the quality of instant not of on something else
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and it has structure confer control flow or with if
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else it's rhyme but is also has full blown expressions
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um liked the um the the times operator and
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the and the the best call an inside the subtraction
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and basically type system is very similar to that of java or at this point
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so it's objects i mean classes and interfaces without
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type parameters that's all you raise the way and primitives
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okay so let's take the s. r. a. r. and compile it you web as someone so um
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we can start at the top at the top of the function um look
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at the if else is structured and we can compile it down to the structured
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um control flow if else of about somebody so far so good
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then um you can see that's the that if in web
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awesomely is annotated with the um artery to which means that the
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result of stiffs of this if else is expression that returns
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an industry too so it's like it's got a lot if else
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our egg can be expressions and can return value if we can
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compile the condition of the if which comes did for the structured if
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because it's going to put on the stack it would in value that says yes or no
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and so how we compile these things is
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we loads the local viable zero which is an
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we and we put it on the stack then we put the constant zero on the stack and
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then we compare the two things on top of the stack and we put back the results and then
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the if is going to pop the wooden value of the stack and
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if it's true answer the denver engine otherwise under the outstretched as part
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um so into that branch it's really easy we have
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that constant one we can load it put on the stack
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and it's it's so that thing that's that's on the stack at the end of the ten branch is going to be
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the result of the if expression like a on the indy else parts we can look at what's the out the the top
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most um operation it's the times so the very and we're
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going to say multiply the two things there on top of the
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stack and on the left we have the local variable and
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witches so we load the local zero put it on the stack
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on the rides we first need to compute the argument to the methods solo dan
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put one on the stack subtracts and we get something else on the stack which
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is then going to be the arguments to the call to the recursive call to factorial
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and then the results of that call will be on top of
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the stack so we can multiply the and the the two bodies
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so this is the this is really how it works so so far it seems like we're good right
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the transition from those colleges i. r. a. two web assembly as looks easy super easy
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we can even now uh do it a recursive factorial
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because otherwise someone will kill me at some point um mm
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so this is the tail recursive factor or would not come later and it's if you comply with discourages i. r.
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uh with this gorgeous complied or you get the i. r. that's at the bottom it is further complicated it's uh it has a
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q. weird things like those labelled blogs this x.
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in this whatever thingy then while through and then inside has returns
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but with the label that's like the name of a blog anyway we're going to look
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at it i don't really want to go into too much detail of how this really works
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but we have this weird construct which is this little blog and the returns
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and the fun part is that whereas somebody that has exactly the same weird construct that
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nobody invented before intelligence invented it and what doesn't invented it and then get to the
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same thing um so it's really nice because that means that when we come past deleterious
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to web assembly we can nab one to the other because they mean the same thing so
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ah here we make we can compare this thing um first we're going to look at the
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local horrible decorations we're going to let them out at the top because we're about somebody only has
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um look of our baltic or that that the top of the of functions
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and then we start from the outermost i'm a part of the method
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and we encountered is labelled block so we inmates
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in web assembly a block whose name is dollar x.
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and the return value of the block will be a in street you
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and then inside we have this loop uh which is a while true so with loops indefinitely
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so basically uh it wasn't you what you would do is have a a loop construct that has a name
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at the at the end of the loop you branch
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back to the group label so was going to look indefinitely
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except of course if from with analogue at some point you accept it in the more brutal fashion
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it's a inside when carter another labels block but this one
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it returns um avoid or units uh or or whatever
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so we translated to simply a label blocking where personally
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and we have the same kind of if ah expression here
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so same thing is before and the if is an expression
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again we loads on the local which is like a moderator
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then we have this thing to load and put one subtract store
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same thing with that multiplication boring and then we have this thing where we just move things around
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um by loading locals and setting locals somewhere else and finally
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we have the return thing which is really like jump at
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a break from this label so that's what we say um break from
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this label in without somebody and it's the same thing it's it's amazing
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and we have the same with the uh with the return but this return
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takes actually a a parameter and that will be the return value of the block
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so at the agenda the if else here it's it's
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an expression if else with it put something on the stack
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and this branch is going to pop that thing from the stack and return it as the results of the big
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block that's artworks anyway uh there was just to show
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off that's starches somewhere that's only ah have the same kind
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of control flow so here for that i now things get
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more complicated um classes as you know it's colour has classes
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i'm here is the non jeez classes the final classed
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meant and we haven't met that that just makes a point
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and this is how you would be compiled into storage is i. r. so you can see
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ah on a class that extends object has
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fielded has accessories for these fields yeah the constructor
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which takes to ins puts them into this and call the super
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constructor it's really boring um and this is how you would somehow or
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compile this to web assembly using the linen memory um so the
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important thing here which apparently i forgot to highlight on the slide is
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on the fact that we have a call to
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dollar matlock so we're actually like allocating memory from
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the litter memory and then we're putting things inside oh and and we end up with a pointer
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related to to to the class and we have to store thing is like a reference to what
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class there's says and then we store the values it's it's right we can we call the constructor
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all of that kind of stuff and he was the body of the constructor
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which uh also called the super constructor and then stores
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things inside the fields that's relatively uh straightforward if you
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imagine that an object leaves and a linear he and you have memory that you have to fill in i.
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e. and the and the f. we have a lot of things that we need to encode from job from
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oh oh well java hours colour is the same thing
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basically at this point of virtual dispatch interfaces garbage collection
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you can implement all of that um it's possible uh it's very tedious
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but it's doable and then uh uh columns c. d. into per interoperable
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eighty probably um and uh this is this is the attack of one
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of a half the monsters of of the c. but uh yep um so
00:22:01
here is the simplify it's scenario and colour g. s. where would
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use the uh javascript timers especially the the global function set timeout i
00:22:12
give it a function i give it a delay which is basically a number
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and this is how we would become pilots to discard his i. r. so you have on your gets
00:22:23
um we have access to the global set timeout function and then we have a call
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and then we have uh and i wrote them down so basically uh uh javascript anonymous function
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that land uh oh calls on other methods
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and that method also gets to global console object
00:22:41
called the log methods with apartment or hello as
00:22:44
the un arguments i and hear things are problematic because
00:22:52
just look at the at at the last line
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which tries to write hello on the console this thing
00:23:00
runs to re to read access to global javascript value him
00:23:05
which is an object it's console problem there is no such
00:23:10
thing as an object in whether someone so you can't even
00:23:14
take that in your hands it there you have no handle to this thing
00:23:18
which is the javascript objects you can not gonna talk about it in web personally
00:23:23
you have strings you cannot talk about strings and where that's only what you can put this array of
00:23:29
cars in the memory but those are not just of strings there's the strings you
00:23:34
cannot hold in your hands of java scripts trying so you're stuck there as well
00:23:39
and then and then you have this this method call to reach out a script foundation which is which is
00:23:45
even more complicated like we would we can't even talk about the the things that that make up this
00:23:51
function call letter the function call itself and the ball of like imagine like you have a higher order
00:23:57
function like what what you do with these things so what that's only just just this in have you
00:24:05
billy to talk about these things it you you
00:24:10
can't you can't get access to any of these things
00:24:13
so if you write as god is like it's completely it's it's it's done right
00:24:20
so are we completely stalk like is the end of the talk
00:24:23
and uh um well there are a few things we control our
00:24:28
one is let's drop inter operability um maybe i don't know
00:24:35
um but the other monster if we do that says
00:24:40
well we basically lose all attempts of any kind of a portability of of
00:24:45
our code right that it's got just go there has been written for uh for
00:24:49
um several years just won't work and what you end up with actually
00:24:55
is a different language um you you basically drops in probably from saudi s.
00:25:01
which was the sole uh which i mean for which interrupt was caught um
00:25:05
the souls got is so what you get instead is another language you might
00:25:10
have heard about it's it's cold and your idea it's gonna native uh
00:25:20
and this is the the the third language that that you might want to
00:25:23
experiment with others coloured it in there is coloured isn't and there's gonna native
00:25:26
it's it's the third language that language uh can be compiled web as only
00:25:31
but that language doesn't talk to javascript so it's a different it's different
00:25:35
language different trade offs and that's not my project so i don't care
00:25:43
okay so now what we're what we're good it would do instead
00:25:46
well basically an n. y. them birds for even one do that
00:25:50
the wise in that is available today in your browsers are we are actually completely
00:25:56
starch there is nothing we can do about it who says god is is that
00:26:03
um but it's there is hope and proposals for future versions of of
00:26:10
web as somebody so now we start looking into the future
00:26:15
of what might be possible and there is
00:26:18
one um proposal which is about reference types
00:26:25
you can go and click on that link if you want um but i'm going to present
00:26:31
a bit what it does so basically the reference types proposal it is an extension to ads well
00:26:37
basically one type to web assembly which
00:26:40
so far had a integers floats and doubles
00:26:45
and now it has four types it has also any ref and and
00:26:51
and a ref is a reference to some thing from the host environments
00:26:58
it could be did javascript keep for example so it could be
00:27:02
a reference to jostle objects or it could be referenced which awesome string
00:27:06
or it could be referenced were javascript number because
00:27:11
that's also eighty javascript thing from the host environment
00:27:16
and you can have um you can have any ref in on the
00:27:21
stack 'em before local horrible for parameters to functions that is all the functions
00:27:27
and you have also a separate he is distinct from the lunar memory
00:27:32
in which you can store any reps so you still have the giant every of by its which
00:27:37
is that in a memory uh on which you can basically puts bites and then there was another array
00:27:44
um of any wraps it but you can not put any rests inside the linear
00:27:51
memory that's not possible and you cannot cast in any ref to an into pointer
00:27:56
either because otherwise the jaw scripts g. c. would have issues okay so what can we do with that
00:28:04
uh well let's look uh this look again at
00:28:08
our hello methods which was are impossible to get before
00:28:15
now it's it's only very awkward um so
00:28:20
what we can do as decompose the things
00:28:23
so the first thing we need to to do is reach the global horrible console
00:28:28
and for that on the web s. and decide on the right on um well you can't really
00:28:34
there is nothing in web assembly even with reference types that lets you
00:28:37
access a global variable from javascript younger thing you can do with imports
00:28:42
so um functions from javascript so you can write a function in javascript on the left
00:28:49
that is called get console that returns the console and you can
00:28:53
import that function from web assembling and then you can call that function
00:28:58
it doesn't take any part either and we'll put on the stack the result the function which is the console objects which isn't any ref
00:29:05
okay so for cigarettes um then i have to puts the
00:29:10
uh this to the string log on on the on the stack
00:29:15
but what that somebody doesn't know how to create a javascript string
00:29:20
but not it's not a problem we can write to
00:29:22
javascript function that returns the constant um log which is a
00:29:27
string and we can import that function and we can call that function and we receive the string as an any ref
00:29:34
that we can do the same with the other constants in our program like the string hello
00:29:39
and finally when we've put those three things on the stack
00:29:43
the the console object the log string and and uh hello strain
00:29:47
we want to call the methods but we're definitely doesn't know how to call it javascript met it but it's not a problem you can write
00:29:55
a job to function that is going to call it that it and
00:29:59
you call that method call method one it takes an object a matter it's
00:30:03
an an argument and is going to call the methods and then you
00:30:07
can import that function from what i somebody and you can call it
00:30:12
so you've called things from javascript outside to put things on your stack
00:30:17
and you called another jostle function to actually use those things from your stack
00:30:22
so let's get right we manage to fruit some fan
00:30:27
um which is a a step to step up from before
00:30:31
what how um let's look at the uh at the set time not playing with with the lambda right click can
00:30:37
we do something about that and uh it's it's very
00:30:42
awkward but uh we can we can creates a function in
00:30:47
so actually that this one is relatively easy 'cause it doesn't have any captures
00:30:52
so we can actually um write a function on on your right
00:30:58
with a on which is why personally function that is the
00:31:01
lambda and it's doesn't take any argument and returns an m.
00:31:05
f. a. called the the other uh the the the the
00:31:08
other actual method and you can actually use this ref that funk
00:31:13
uh upper operation in web as an we
00:31:16
to get eighty javascript version of that function
00:31:22
so that's possible but only because it doesn't have captures but that's that's already quite good
00:31:28
so you can put that on the stack up and then you can put the constant uh one thousand does double
00:31:35
on the stack but then um are you cannot actually give
00:31:40
that to javascript actually is not in a relatively generic way
00:31:44
because what you want is really any wraps so what you need is a function that takes a double
00:31:50
and returns and and a ref for that double and what doesn't it doesn't have an operation for that
00:31:56
but no problem you can write a function in javascript on the left which is called box double that takes up
00:32:03
a double and we change the same thing so that was useless rates
00:32:08
except that if you look at the right we give up a type
00:32:11
two that function from web assembly side and we say it takes as
00:32:15
a parameter and have sixty four so double and a retraction any ref
00:32:20
and because of how what gasoline javascript talks which other the double that was on the stack will be
00:32:26
given as an f. sixty four to javascript refrigerated into a primitive number
00:32:31
and we returns to to where that's only which expects in any ref
00:32:34
that number will be interpreted as an any rev version of that number so yeah it for that
00:32:41
no that we had those things on the stack we can we can use a similar mechanism to actually call the function et cetera et cetera
00:32:48
okay so so we can do that but he was a real proper of
00:32:54
uh references across sleeps because ah remember it'll do that and the rest you can put
00:33:00
them on the stack and on the separates keep you cannot put them inside the linear memory
00:33:09
so i told you we were going to come back to this example angie with
00:33:13
this command a vision of the references across the two heaps that we need here
00:33:19
um we need in in the dallas would keep idea they we end up with a done event
00:33:24
listeners thing from from the browser which reference land down which is a task on a transfer function
00:33:30
that doesn't function in its captures hold a um has access
00:33:36
to the the states thing which is an instance from discover he
00:33:40
and that thing contains a value points which is a g. s. a race so it
00:33:44
comes from the javascript heap and that thing again contains points which are things from this collection
00:33:51
so now you have a on the s. s. thing and
00:33:57
it's well i from pointers from the javascript heaped use colour heap
00:34:03
well the only thing we can remember that on the skull heap objects are just pointers in the random memories
00:34:09
to basically their numbers so yeah you could you can
00:34:14
hold a number in and out a script that's okay
00:34:17
but the problem is then that this colour g. c. can
00:34:21
not know which objects are reachable or not switching navigable collect anything
00:34:26
and then the the other arrows from started javascript since we cannot put any resin
00:34:31
that either memory what we're going to do is put ideas integer ideas that are basically
00:34:37
he's in the mapping javascript double actually map to the real objects from the javascript side
00:34:43
but then the javascript g. c. can never know when these things are not or any reachable
00:34:48
you can make this work to some extent but if you do have cycles at some point
00:34:54
then it's it's that like your cycle your cycles in never going to be collected
00:34:59
and i don't even want to talk about the performance aspect of
00:35:02
these things um so what you really need at some point is full
00:35:08
cooperation between the two g. sees the g. c. from the web
00:35:12
that somebody's got aside and the g. c. from the javascript our sides
00:35:17
big use unit to support cycles between um between that
00:35:21
usually dislikes got eyes full of cycles jaw successful cycles
00:35:25
um is coverages is full cycles between the two so if
00:35:29
we don't have support for cycles it it's it's a no go
00:35:34
so with any reps alone we can get far we can actually get something that is
00:35:41
correct that will implement the entire psychology a specification
00:35:47
correctly but there was just one little cafe yet
00:35:52
it won't garbage product if i don't know might be good enough for your ah okay so today and then what
00:36:03
well it was another proposal for web as only for
00:36:07
t. c. um so i'm very happy about this one it's
00:36:12
at the very vague stage though so but there is a
00:36:16
document that says more or less what they want to do
00:36:21
and basically what they want to do with you things they want new types ah in
00:36:25
addition to the integers the floats and the and the revs they want so balls and arrays
00:36:32
and then they want references to those things so you can have
00:36:36
it's not a pointer to reference no reference to double or reference
00:36:41
to an array and those references will
00:36:47
supposedly be garbage collected slide you can actually
00:36:50
creates a garbage collected heap in web as somebody that will be taken care off by the
00:36:56
web s. only g. c. and that one is a is designed to cooperate with the chastity
00:37:03
and it doesn't t. c. so that's good so let's let's look at what we could do
00:37:08
here i'm i'm so for for the uh for the class points which has a two ins
00:37:15
we would define a out two types first the type point destruct which
00:37:20
defines the the internal representation which is actually three ins not just to um
00:37:28
the first one is just the uh an identifier for the class point
00:37:33
'cause we need to remember that for instance off and that kind of stuff
00:37:36
and the two other ins or the actual x. and y. and then we define another type
00:37:40
which is point which we define as a reference to a points tracked and the state is similar
00:37:48
i'm here it has are we construct
00:37:52
within in switches again the class states
00:37:55
and and and the ref um because that's a that's
00:37:59
a job as a reading so here in in destruct
00:38:04
we can actually you have any rests in this time right so we can have
00:38:10
jeez eat objects in web assembly that actually refer directly
00:38:15
to g. c. stuff from the javascript world and vice versa
00:38:20
so yeah for that so if we if we had that we're probably will
00:38:27
have it at some point this is what we can do um the frog
00:38:32
is ah so first we create an an empty re but of course java
00:38:37
web s. and it doesn't know how to create an anti jobs array but
00:38:40
that's okay you can you can write a function in doubted that
00:38:43
creates an enduring returns to jot to to it doesn't we uh as
00:38:47
a as an any ref right and you can put it on the
00:38:49
stack okay um then there is a locating an instance of of state
00:38:57
first you would put on the stack the the identifier the that
00:39:01
that's uh for the class state and then you put a and all
00:39:06
on the stack which will be the initial value of the of the
00:39:08
plants field and and then you call this this new this operator from
00:39:15
web as somebody with ah with the g. c. proposal which is new
00:39:20
and then you give the type of destruct and that will uh locate obstruct with the initial values
00:39:26
taken from the stack and which are new a reference to that starts not the pointer or reference
00:39:33
and then you can call the constructor which will take the reference fit
00:39:37
in the of food in the on the field et cetera so that's good
00:39:41
and later when you want to create the land that that that has captures
00:39:45
he has a capture of type states which is the javascript um as colour object
00:39:50
and the reference um uh dave which is anything because it just
00:39:54
javascript thing you can actually do that um all you just have to
00:39:59
well it's whether somebody doesn't really know how to create captures for functions but that's okay you can
00:40:05
write a job as a function of the work capture things for you and you can call it um
00:40:11
and this is how you how you do it so basically if we have this
00:40:14
this cheesy proposal at some point will be able to encode all off colour g. is
00:40:18
to web assembly with reference types and a. g. c.
00:40:21
proposal in a way that's correct and um and that actually
00:40:27
garbage collect which would be a good thing so when do
00:40:33
we get this well first we need the reference types proposal
00:40:37
which is at the stage called implementation stage currently four of us and we
00:40:41
in so that means the um the engines are in court just to implement that
00:40:48
whatever the spectre is at the moment so that we can
00:40:50
get feedback on the proposal and uh so for as far as
00:40:55
i know um the uh the firefox engine implements the the
00:40:59
current state of reference sites then uh we need stitches a proposal
00:41:05
and that one is at a very early stage there is there isn't even a speck at this point it's
00:41:10
ideas emmy ideas for type system i'm more or less
00:41:15
specified but not really so that will take some time
00:41:21
and and the men that on there and then we can actually implement that
00:41:25
the um the supports in in scarred as or at least we hope to
00:41:29
actually do that in in colour with the development of g. of the just
00:41:32
a proposal so that we can feed back into the proposal if something is
00:41:37
is wrong for us so it will still take a while i'm sorry about that
00:41:44
so that's all i had um i'm happy to take one or two questions i think we have a few minutes
00:41:51
thanks
00:41:56
hi microphones common
00:42:02
there's little clues was no i'm i'm wondering because the there's another path
00:42:07
that can be taken but i wonder what where you cannot be taken here
00:42:10
uh for example maybe useful what um i think it's a stir use the name of the products which is
00:42:15
really did you she beckoned that goes to was an unnerving will be doing the the the story allows
00:42:20
the view the values between uh is it because those colours not preferentially transparent that you can uh dude
00:42:28
there is a um yeah so so certainly if you're languages entirely um
00:42:36
um preferentially transparent you can you can do that relies arenas and you have an overall
00:42:42
so you'll have to implement in the was under the new console logon for but it's a
00:42:47
bit of a lie though because what if you need to uh see rely is the
00:42:53
value of type io well you never do that as well as go you never knew that
00:42:59
yeah but the the thing is like this is the kind of expressive it see in
00:43:03
terms of communicating with javascript that's got his hands and that the uh language that there's ins
00:43:10
um doesn't have this this binary synchronise inter probably would javascript like
00:43:15
everything you can do in johnson you can do we discovered is
00:43:18
if i if you if you cannot see relies on an io basically
00:43:22
estate in between two calls to javascript well what would be you know
00:43:27
could use clues of that the what were you will need to send
00:43:29
that through the small snow but they show their your which inter leaves
00:43:34
calls to mutable javascript it's uh things and my own
00:43:38
code and then calls again something from the dos well
00:43:41
then when you are in was um how can you cool blue to external world who can you launched missile right
00:43:47
uh that you can do that because you can import also functions which we did with the
00:43:51
import a statement yes we hold it yes i mean if you pick up a few to you
00:43:56
all the regular communication between that's info interface right it's uh it it gets
00:44:01
um it gets an an an unwieldy in uh and at some point you realise
00:44:07
you can't get everything right but if you want to begin with and talk further uh of line
00:44:13
any other question that they're the back
00:44:20
uh_huh i sebastian uh so i guess like i should be this new let you presented good luck but
00:44:26
would what would be the advantage gained all of the car and encoding i is it was a big
00:44:32
changing including and possibly all the all the heads for the all the stuff that
00:44:36
you of all still didn't know that it just moved to a different one time passes
00:44:40
well we already have now is up in a transition to dallas get
00:44:45
uh you know the pros and cons of the two approaches given that people can work
00:44:50
well i um nobody where nobody really knows um if you if you ask random
00:44:56
people on the internet they will say compared with that somebody is going to be fast
00:45:03
no that's not how it works um if you compile
00:45:07
c. to web vaseline is going to be fast relative
00:45:11
to compiling c. to to javascript because compared to see
00:45:15
javascript has too many features and and we covering them from
00:45:21
to the level of c. is is is problematic to that is why wasn't wasn't button in the first place which is
00:45:27
going from city where that's only you don't have the impedance mismatch we're not losing banks
00:45:33
are also not gaining anything um if you compare the garbage collected language to address only
00:45:41
ah with the g. c. proposal uh hopefully you expect
00:45:45
to not lose things and that's how you get performance
00:45:49
you you all again performance aware that's only because going from your source language you're not using things
00:45:55
so why would we not what things would we not reduce
00:45:58
well we wouldn't lose for example are types or does or monolithic
00:46:02
types the same the same kind of times we have that on the g. d. n. so as long as you were staying
00:46:08
and you compute intensive for sound portion off your program that only many pretty it's gotta types
00:46:14
you remain in the realm of web assembly where everything is statically typed
00:46:19
n. t. re you can get something similar performance to the j. v. m.
00:46:24
except that of course the j. v. m. is going to do polymorphic in lying it comes things with age
00:46:30
in where that's on the right now is still a no go ahead you you cannot you cannot do um
00:46:35
mm a profile bayes optimisation zap fun time like
00:46:40
this is uh this this is not happening yet so
00:46:46
i think we we can gain if if we all of this happens is
00:46:50
for the large portions of starches programs that actually stay
00:46:55
within this colour um subsets those will basically perform better
00:47:04
but if you have a portion of just gorgeous problem just constantly talk to javascript back and forth
00:47:09
that might actually lose performance art because it would it's constantly like cross
00:47:14
the boundary between web assembly in java scripts and depending on how that's implemented
00:47:19
uh the engine level we could lose performance or at least we want to gain anything that's that's that definitely it
00:47:25
and then for things like virtual dispatch and and and and you know lining of those things
00:47:30
it's a it's an clear the futurists all very much uncertain at this point i
00:47:41
do you think you for the dog um maybe a crazy cushion
00:47:48
so uh do you think it's possible to uh um uh
00:47:52
to compile that you've been itself will bustling yes it's been done
00:47:59
so then this carriage is called can be a a can be
00:48:03
combined called and did you busy the can interpret nope half a um
00:48:11
this colour t. v. um source code can become byte code and can be interpreted by the g. d. m.
00:48:17
but again it's the same problem is with its colour native it's a different language
00:48:22
and if you write colour j. v. m. code you can call
00:48:25
java libraries but you cannot call javascript libraries you cannot manipulate the dawn
00:48:29
you cannot manipulate your web page you cannot use does aliens and p. m. packages out there
00:48:36
so again it's important to go back to the semantics of your
00:48:39
language and remember that psychology um start is is gonna is if
00:48:44
or three different languages with different semantics and different capabilities
00:48:49
and yes you can compare digit into web assembly and you can run psychology in
00:48:52
code on that t. m. you cannot runs colour j. s. code on the t. m.
00:49:01
the last question
00:49:03
oh and thanks for talk ah and sounds very exciting i look forward to
00:49:08
things happening in my bass and lisa they can also happen in his college yes
00:49:13
i was wondering if uh on the language scaling woodside
00:49:16
we got a f. x. with that uh improve the
00:49:19
performance r. r. x. oppose opportunities for certain kinds of
00:49:23
optimisation since we mention what d. c. is able to do
00:49:27
and also obviously garbage collection here is important so if you could establish a that it's
00:49:32
certain parts of code onto certain things ah how much do you think this is good help
00:49:39
or to not i'll always optimise for worst case do you have funding for p.
00:49:43
h. d. students um um the mm i i i i think it's a it's a
00:49:52
it's really research topic they we we we we we don't know how to how
00:49:56
to do these things like given the current hardware and the currents of to my there's
00:50:02
and uh it's it's still unclear words in effect system is
00:50:06
actually able to provide in terms of uh of optimisation is
00:50:10
in general so let alone in the constraints and norman's of of web as only
00:50:16
i think this is the um it's it's worth thinking about it the yeah as my
00:50:21
initial answers it just it it and it's probably worth and five p. h. d. oh yeah
00:50:29
thanks okay uh i'm i'll be happy to take
00:50:31
further questions uh here or
Conference Program
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753 views
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276 views
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Mellite: An Integrated Development Environment for Sound
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Closing panel
Panel
June 13, 2019 · 5:54 p.m.
400 views