Re: Syntax sugar for partial application
On Mon, Apr 13, 2015 at 12:15 AM, liorean lior...@gmail.com wrote: On 12 April 2015 at 17:39, Jussi Kalliokoski jussi.kallioko...@gmail.com wrote: No, «this» is lexically bound to be that of the enclosing lexical scope in arrow functions, so it would be whatever that is. But that doesn't really matter as the function call to «foo» doesn't use the «this» of the arrow function. Exactly why you get `null` as `this`. Which makes the behaviour identical to that of the code as you wrote it. If you looked at the gist I made, the placeholder syntax creates functions where `this` remains untouched, so it can be separately bound, unlike in your examples. See [1] for example of how the syntax desugars to ES6. Now, if we were to say your «foo» were actually «foo.bar», and you did the same replacement in the arrow function, the «this» value of the «bar» call would be «foo», so that's pretty much what is wanted as well. The case where this breaks is if you were to replace only the «bar» method with the arrow function, in which case it would use the lexical «this» instead of «foo», but that's obviously not the right transformation to use. This might not seem like such a big deal until you consider it in combination with the proposed bind syntax [1]. Also in your examples, redefining `foo` will lead to different results. The placeholder syntax has a lot more room for optimization in the JIT compiler (the partially applied result is guaranteed to have no side effects for example, so the compiler can create a version of the original function where it can inline the specified arguments; less moving parts, easier to optimize). Yeah, it's susceptible to that problem, yes. Do you want me to fix that for you if you really want it? Your «foo(1, ?, 2);» is equivalent to «((f,a)=f(1,a,2))(foo)». Your «foo(?, 1, ???);» is equivalent to «((f,a,...b)=f(a,1,...b))(foo)». Your «foo(1, ???, 2);» is equivalent to «((f,...a)=f(...[1,...a,2]))(foo)». Your new examples directly execute the function instead of creating a new function. :) Which goes to show how it would be nice to have specific syntax for this to make it more obvious what's happening. Oops. I needed to actually add that extra argument as a separate fat arrow, «(f=(...a)=f(...[1,...a,2]))(foo)» etc. I write my code pretty much the same way. However, it's hard for the compiler to trust that you're not changing things, regardless of style. Guess it'd be hard for it unless it has the knowledge of whether functions are pure or not, yes. I'd love for a compiler that can tell that I don't modify my arguments and thus optimises code like « let map= // Usage: map(function)(...array) (f,...acc)=(head,...tail)=( undefined===head ?acc :map(f,...acc,f(head))(...tail)); » So that it doesn't actually create the «tail» array every recursion, just a narrower and narrower subarray of the same actual array, and likewise that the only thing that is done with «acc» is the production of an array that is identical to it with an addition of one element at its end, so doesn't break it down and rebuild it every recursion. And of course tail call optimisation on it, because that code is horrid without those optimisations. Me too, yet while nothing is impossible, this sort of optimization (tail call optimization aside) would be super difficult to implement, and expensive too, because the compiler would have to check that the invariants weren't violated on every call. However, there is hope in the light of immutable collections proposals where the compiler has solid guarantee that the collection isn't morphed mid-iteration and can safely use a cursor to a sub-collection. [1] https://gist.github.com/anonymous/5c4f6ea07ad3017d61be#leading-placeholder -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Syntax sugar for partial application
On Sat, Apr 11, 2015 at 4:54 AM, liorean lior...@gmail.com wrote: On 9 April 2015 at 16:11, Jussi Kalliokoski jussi.kallioko...@gmail.com wrote: On Thu, Apr 9, 2015 at 4:04 PM, liorean lior...@gmail.com wrote: Do we really need it? Your «foo(1, ?, 2);» is equivalent to «a=foo(1,a,2)». Your «foo(?, 1, ???);» is equivalent to «(a,...b)=foo(a,1,...b)». Your «foo(1, ???, 2);» is equivalent to «(...a)=foo(...[1,...a,2])». Not exactly. Using the placeholder syntax, `this` remains context dependent, whereas with your examples you get `null` as `this`. No, «this» is lexically bound to be that of the enclosing lexical scope in arrow functions, so it would be whatever that is. But that doesn't really matter as the function call to «foo» doesn't use the «this» of the arrow function. Exactly why you get `null` as `this`. Now, if we were to say your «foo» were actually «foo.bar», and you did the same replacement in the arrow function, the «this» value of the «bar» call would be «foo», so that's pretty much what is wanted as well. The case where this breaks is if you were to replace only the «bar» method with the arrow function, in which case it would use the lexical «this» instead of «foo», but that's obviously not the right transformation to use. This might not seem like such a big deal until you consider it in combination with the proposed bind syntax [1]. Also in your examples, redefining `foo` will lead to different results. The placeholder syntax has a lot more room for optimization in the JIT compiler (the partially applied result is guaranteed to have no side effects for example, so the compiler can create a version of the original function where it can inline the specified arguments; less moving parts, easier to optimize). Yeah, it's susceptible to that problem, yes. Do you want me to fix that for you if you really want it? Your «foo(1, ?, 2);» is equivalent to «((f,a)=f(1,a,2))(foo)». Your «foo(?, 1, ???);» is equivalent to «((f,a,...b)=f(a,1,...b))(foo)». Your «foo(1, ???, 2);» is equivalent to «((f,...a)=f(...[1,...a,2]))(foo)». Your new examples directly execute the function instead of creating a new function. :) Which goes to show how it would be nice to have specific syntax for this to make it more obvious what's happening. I guess I didn't think of these cases though, because I only use explicit arguments to my functions these days, I never use the «this» keyword. If I want a function to operate on an object, I pass that object into the function. I also try to not reuse my variables unless they are part of an iteration, in which case they are always local variables that are only handled in the iteration process itself. But that's a side issue, as it's about my code rather than precepts of the language. I write my code pretty much the same way. However, it's hard for the compiler to trust that you're not changing things, regardless of style. Also because most of the standard library of the language operates on `this` instead of a separate argument, combining standard library methods with methods that have their data as an explicit argument often lead to awkward reading order issues, e.g. foo(x .filter(...) .map(...) .reduce(...) ) whereas with the bind operator you get x .filter(...) .map(...) .reduce(...) ::foo() Which is where this proposal shines, if foo is a partially applied function. But anyway, seems that this is not something people want, at least yet, so I'll rest my case. :) -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Syntax sugar for partial application
On 12 April 2015 at 17:39, Jussi Kalliokoski jussi.kallioko...@gmail.com wrote: No, «this» is lexically bound to be that of the enclosing lexical scope in arrow functions, so it would be whatever that is. But that doesn't really matter as the function call to «foo» doesn't use the «this» of the arrow function. Exactly why you get `null` as `this`. Which makes the behaviour identical to that of the code as you wrote it. Now, if we were to say your «foo» were actually «foo.bar», and you did the same replacement in the arrow function, the «this» value of the «bar» call would be «foo», so that's pretty much what is wanted as well. The case where this breaks is if you were to replace only the «bar» method with the arrow function, in which case it would use the lexical «this» instead of «foo», but that's obviously not the right transformation to use. This might not seem like such a big deal until you consider it in combination with the proposed bind syntax [1]. Also in your examples, redefining `foo` will lead to different results. The placeholder syntax has a lot more room for optimization in the JIT compiler (the partially applied result is guaranteed to have no side effects for example, so the compiler can create a version of the original function where it can inline the specified arguments; less moving parts, easier to optimize). Yeah, it's susceptible to that problem, yes. Do you want me to fix that for you if you really want it? Your «foo(1, ?, 2);» is equivalent to «((f,a)=f(1,a,2))(foo)». Your «foo(?, 1, ???);» is equivalent to «((f,a,...b)=f(a,1,...b))(foo)». Your «foo(1, ???, 2);» is equivalent to «((f,...a)=f(...[1,...a,2]))(foo)». Your new examples directly execute the function instead of creating a new function. :) Which goes to show how it would be nice to have specific syntax for this to make it more obvious what's happening. Oops. I needed to actually add that extra argument as a separate fat arrow, «(f=(...a)=f(...[1,...a,2]))(foo)» etc. I write my code pretty much the same way. However, it's hard for the compiler to trust that you're not changing things, regardless of style. Guess it'd be hard for it unless it has the knowledge of whether functions are pure or not, yes. I'd love for a compiler that can tell that I don't modify my arguments and thus optimises code like « let map= // Usage: map(function)(...array) (f,...acc)=(head,...tail)=( undefined===head ?acc :map(f,...acc,f(head))(...tail)); » So that it doesn't actually create the «tail» array every recursion, just a narrower and narrower subarray of the same actual array, and likewise that the only thing that is done with «acc» is the production of an array that is identical to it with an addition of one element at its end, so doesn't break it down and rebuild it every recursion. And of course tail call optimisation on it, because that code is horrid without those optimisations. -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Syntax sugar for partial application
On 9 April 2015 at 16:11, Jussi Kalliokoski jussi.kallioko...@gmail.com wrote: On Thu, Apr 9, 2015 at 4:04 PM, liorean lior...@gmail.com wrote: Do we really need it? Your «foo(1, ?, 2);» is equivalent to «a=foo(1,a,2)». Your «foo(?, 1, ???);» is equivalent to «(a,...b)=foo(a,1,...b)». Your «foo(1, ???, 2);» is equivalent to «(...a)=foo(...[1,...a,2])». Not exactly. Using the placeholder syntax, `this` remains context dependent, whereas with your examples you get `null` as `this`. No, «this» is lexically bound to be that of the enclosing lexical scope in arrow functions, so it would be whatever that is. But that doesn't really matter as the function call to «foo» doesn't use the «this» of the arrow function. Now, if we were to say your «foo» were actually «foo.bar», and you did the same replacement in the arrow function, the «this» value of the «bar» call would be «foo», so that's pretty much what is wanted as well. The case where this breaks is if you were to replace only the «bar» method with the arrow function, in which case it would use the lexical «this» instead of «foo», but that's obviously not the right transformation to use. This might not seem like such a big deal until you consider it in combination with the proposed bind syntax [1]. Also in your examples, redefining `foo` will lead to different results. The placeholder syntax has a lot more room for optimization in the JIT compiler (the partially applied result is guaranteed to have no side effects for example, so the compiler can create a version of the original function where it can inline the specified arguments; less moving parts, easier to optimize). Yeah, it's susceptible to that problem, yes. Do you want me to fix that for you if you really want it? Your «foo(1, ?, 2);» is equivalent to «((f,a)=f(1,a,2))(foo)». Your «foo(?, 1, ???);» is equivalent to «((f,a,...b)=f(a,1,...b))(foo)». Your «foo(1, ???, 2);» is equivalent to «((f,...a)=f(...[1,...a,2]))(foo)». I guess I didn't think of these cases though, because I only use explicit arguments to my functions these days, I never use the «this» keyword. If I want a function to operate on an object, I pass that object into the function. I also try to not reuse my variables unless they are part of an iteration, in which case they are always local variables that are only handled in the iteration process itself. But that's a side issue, as it's about my code rather than precepts of the language. -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Syntax sugar for partial application
On Thu, Apr 9, 2015 at 4:04 PM, liorean lior...@gmail.com wrote: Do we really need it? Your «foo(1, ?, 2);» is equivalent to «a=foo(1,a,2)». Your «foo(?, 1, ???);» is equivalent to «(a,...b)=foo(a,1,...b)». Your «foo(1, ???, 2);» is equivalent to «(...a)=foo(...[1,...a,2])». Not exactly. Using the placeholder syntax, `this` remains context dependent, whereas with your examples you get `null` as `this`. This might not seem like such a big deal until you consider it in combination with the proposed bind syntax [1]. Also in your examples, redefining `foo` will lead to different results. The placeholder syntax has a lot more room for optimization in the JIT compiler (the partially applied result is guaranteed to have no side effects for example, so the compiler can create a version of the original function where it can inline the specified arguments; less moving parts, easier to optimize). [1] http://wiki.ecmascript.org/doku.php?id=strawman:bind_operator Also, the ? token is already taken by the ternary conditional operator. Do we really want to overload it here for a nullary operator/special form, when we have as low overhead syntax as we already do in fat arrows for doing the exact same thing? -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Syntax sugar for partial application
FWIW: agreed with others, it looks a pretty pointless sugar. It doesn't seem to bring anything new or that needed to the language. -1 here On Thu, Apr 9, 2015 at 2:04 PM, liorean lior...@gmail.com wrote: Do we really need it? Your «foo(1, ?, 2);» is equivalent to «a=foo(1,a,2)». Your «foo(?, 1, ???);» is equivalent to «(a,...b)=foo(a,1,...b)». Your «foo(1, ???, 2);» is equivalent to «(...a)=foo(...[1,...a,2])». Also, the ? token is already taken by the ternary conditional operator. Do we really want to overload it here for a nullary operator/special form, when we have as low overhead syntax as we already do in fat arrows for doing the exact same thing? -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Syntax sugar for partial application
Do we really need it? Your «foo(1, ?, 2);» is equivalent to «a=foo(1,a,2)». Your «foo(?, 1, ???);» is equivalent to «(a,...b)=foo(a,1,...b)». Your «foo(1, ???, 2);» is equivalent to «(...a)=foo(...[1,...a,2])». Also, the ? token is already taken by the ternary conditional operator. Do we really want to overload it here for a nullary operator/special form, when we have as low overhead syntax as we already do in fat arrows for doing the exact same thing? -- David liorean Andersson ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
