Perhaps removing the `:` is a bad idea actually? I see now it removes the
consistency on values. Either way, let's not lose the momentum on this! I feel
like we can get this over the line (or put the last nails in its coffin for
good )
On Wed, Jun 28, 2023 at 8:45 PM, Zach Daniel < zachary.s.dan...@gmail.com >
wrote:
>
> I agree with Paul on the specific operator, however I feel like you've
> just done a great thing laying out most if not all of the considerations
> we've had on this conversation to date. I know that these conversations
> can get long and sometimes not produce fruit, but I feel like we should
> try to chase this down and come to a conclusion on the matter if at all
> possible.
>
>
>
> My personal suggestion on the proposal would be to use `$` as you've said,
> and to remove the need for `:` for the case of atoms.
>
>
>
> %{$foo, $bar} = %{foo: 10, bar: 10}
>
>
> %{$"foo", $"bar"} = map
>
>
> It is a new operator, but it feels expressive to me, and the $ currently
> has no use in mainstream elixir syntax (its used in ets match specs as a
> value, not as an operator). That seems like a good solution to me.
>
>
>
>
>
> On Wed, Jun 28, 2023 at 8:45 PM, Christopher Keele < christhekeele@ gmail.
> com ( christheke...@gmail.com ) > wrote:
>
>> > My thoughts on the proposal itself aside, I’d just like to say that I
>> think you’ve set a great example of what proposals on this list should
>> look like. Well done!
>>
>>
>> Much appreciated!
>>
>>
>> > I have an almost visceral reaction to the use of capture syntax for this
>> though.
>>
>>
>> > I think calling the `&…` syntax “capture syntax” is actually misleading,
>> and only has that name because it can be used to construct closures by
>> “capturing” a function name, but it is more accurate to consider it
>> closure syntax, in my opinion.
>>
>>
>> This is a very salient point. How do you feel about introducing a new
>> operator for this sugar, such as $ :foo ?
>> On Wednesday, June 28, 2023 at 7:41:05 PM UTC-5 Paul Schoenfelder wrote:
>>
>>
>>> My thoughts on the proposal itself aside, I’d just like to say that I
>>> think you’ve set a great example of what proposals on this list should
>>> look like. Well done!
>>>
>>>
>>>
>>> I have an almost visceral reaction to the use of capture syntax for this
>>> though, and I don’t believe any of the languages you mentioned that
>>> support field punning do so in this fashion. They all use a similar
>>> intuitive syntax where the variable matches the field name, and they don’t
>>> make any effort to support string keys.
>>>
>>>
>>>
>>> If Elixir is to ever support field punning, I strongly believe it should
>>> follow their example. However, there are reasons why Elixir cannot do so
>>> due to syntax ambiguities (IIRC). In my mind, that makes any effort to
>>> introduce this feature a non-starter, because code should be first and
>>> foremost easy to read, and I have yet to see a proposal for this that
>>> doesn’t make the code harder to read and understand, including this one.
>>>
>>>
>>>
>>> I’d like to have field punning, but by addressing, if possible, the core
>>> issue that is blocking it. If that can’t be done, I just don’t think the
>>> cost of overloading unrelated syntax is worth it. I think calling the `&…`
>>> syntax “capture syntax” is actually misleading, and only has that name
>>> because it can be used to construct closures by “capturing” a function
>>> name, but it is more accurate to consider it closure syntax, in my
>>> opinion. Overloading it to mean capturing things in a more general sense
>>> will be confusing for everyone, and would only work in a few restricted
>>> forms, which makes it more difficult to teach and learn.
>>>
>>>
>>>
>>> That’s my two cents anyway, I think you did a great job with the proposal,
>>> but I’m very solidly against it as the solution to the problem being
>>> solved.
>>>
>>>
>>>
>>> Paul
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Wed, Jun 28, 2023, at 7:56 PM, Christopher Keele wrote:
>>>
>>>
>>>> This is a formalization of my concept here (
>>>> https://groups.google.com/g/elixir-lang-core/c/oFbaOT7rTeU/m/BWF24zoAAgAJ
>>>> ) , as a first-class proposal for explicit discussion/feedback, since I now
>>>> have a working prototype (
>>>> https://github.com/elixir-lang/elixir/compare/main...christhekeele:elixir:tagged-variable-capture
>>>> ).
>>>>
>>>>
>>>>
>>>> *Goal*
>>>>
>>>> **
>>>>
>>>> The aim of this proposal is to support a commonly-requested feature:
>>>> *short-hand
>>>> construction and pattern matching of key/value pairs of associative data
>>>> structures, based on variable names* in the current scope.
>>>>
>>>>
>>>>
>>>> *Context*
>>>>
>>>>
>>>>
>>>> Similar shorthand syntax sugar exists in many programming languages today ,
>>>> known variously as:
>>>>
>>>>
>>>>
>>>> * Field Punning ( https://dev.realworldocaml.org/records.html ) — OCaml
>>>>
>>>> * Record Puns (
>>>> https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/record_puns.html )
>>>> — Haskell
>>>>
>>>> * Object Property Value Shorthand (
>>>> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#property_definitions
>>>> ) — ES6 Javascript
>>>>
>>>>
>>>>
>>>>
>>>> This feature has been in discussion for a decade, on this mailing list ( 1
>>>> (
>>>> https://groups.google.com/g/elixir-lang-core/c/4w9eOeLvt-8/m/WOkoPSMm6kEJ
>>>> ) , 2 (
>>>> https://groups.google.com/g/elixir-lang-core/c/NoUo2gqQR3I/m/WTpArTGMKSIJ
>>>> ) , 3 (
>>>> https://groups.google.com/g/elixir-lang-core/c/3XrVXEVSixc/m/NHU2M4QFAQAJ
>>>> ) , 4 (
>>>> https://groups.google.com/g/elixir-lang-core/c/OvSQkvXxsmk/m/bKKHbBxiCwAJ
>>>> ) , 5 (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/1W-d_XAlBgAJ
>>>> ) , 6 ( https://groups.google.com/g/elixir-lang-core/c/oFbaOT7rTeU ) ) and
>>>> the Elixir forum ( 1 (
>>>> https://elixirforum.com/t/proposal-add-field-puns-map-shorthand-to-elixir/15452
>>>> ) , 2 (
>>>> https://elixirforum.com/t/shorthand-for-passing-variables-by-name/30583 ) ,
>>>> 3 (
>>>> https://elixirforum.com/t/if-you-could-change-one-thing-in-elixir-language-what-you-would-change/19902/17
>>>> ) , 4 (
>>>> https://elixirforum.com/t/has-map-shorthand-syntax-in-other-languages-caused-you-any-problems/15403
>>>> ) , 5 (
>>>> https://elixirforum.com/t/es6-ish-property-value-shorthands-for-maps/1524
>>>> ) , 6 (
>>>> https://elixirforum.com/t/struct-creation-pattern-matching-short-hand/7544
>>>> ) ), and has motivated many libraries ( 1 (
>>>> https://github.com/whatyouhide/short_maps ) , 2 (
>>>> https://github.com/meyercm/shorter_maps ) , 3 (
>>>> https://hex.pm/packages/shorthand ) , 4 ( https://hex.pm/packages/synex )
>>>> ).
>>>> These narrow margins cannot fit the full history of possibilities,
>>>> proposals, and problems with this feature, and I will not attempt to
>>>> summarize them all. For context, I suggest reading this mailing list
>>>> proposal (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/1W-d_XAlBgAJ
>>>> ) and this community discussion (
>>>> https://elixirforum.com/t/proposal-add-field-puns-map-shorthand-to-elixir/15452
>>>> ) in particular.
>>>>
>>>>
>>>>
>>>> However, in summary, this particular proposal tries to solve a couple of
>>>> past sticking points:
>>>>
>>>> * Atom vs String (
>>>> https://groups.google.com/g/elixir-lang-core/c/NoUo2gqQR3I/m/IpZQHbZk4xEJ
>>>> ) key support
>>>>
>>>> * Visual clarity (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/NBkAVto0BAAJ
>>>> ) that atom/string matching is occurring
>>>>
>>>> * Limitations of string-based sigil parsing (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/TiZw6xM3BAAJ
>>>> )
>>>>
>>>> * Easy confusion (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/WRhXxHDfBAAJ
>>>> ) with tuples
>>>>
>>>> I have a working fork of Elixir here (
>>>> https://github.com/christhekeele/elixir/tree/tagged-variable-capture )
>>>> where
>>>> this proposed syntax can be experimented with. Be warned, it is buggy.
>>>>
>>>>
>>>>
>>>> *Proposal: Tagged Variable Captures*
>>>>
>>>> **
>>>>
>>>> I propose we overload the unary capture operator ( & ) to accept
>>>> compile-time atoms and strings as arguments, for example &:foo and *&"bar"*
>>>> . This would expand at compile time into *a tagged tuple with the
>>>> atom/string and a variable reference*. For now, I am calling this a
>>>> "tagged-variable
>>>> capture" to differentiate it from a function capture.
>>>>
>>>>
>>>>
>>>> For the purposes of this proposal, assume:
>>>>
>>>>
>>>>
>>>> {foo, bar} = { 1 , 2 }
>>>>
>>>>
>>>>
>>>> Additionally,
>>>>
>>>>
>>>>
>>>> * Lines beginning with # == indicate what the compiler expands an
>>>> expression to.
>>>>
>>>> * Lines beginning with # => represent the result of evaluating that
>>>> expression.
>>>>
>>>> * Lines beginning with *# !>* represent an exception.
>>>>
>>>>
>>>>
>>>>
>>>> *Bare Captures*
>>>>
>>>>
>>>>
>>>> I'm not sure if we should support *bare* tagged-variable capture, but it is
>>>> illustrative for this proposal, so I left it in my prototype. It would
>>>> look like:
>>>>
>>>>
>>>>
>>>> & :foo
>>>>
>>>> # == { :foo , foo}
>>>>
>>>> # => { :foo , 1 }
>>>>
>>>> & "foo"
>>>>
>>>> # == { "foo" , foo}
>>>>
>>>> # => { "foo" , 1 }
>>>>
>>>>
>>>>
>>>> If bare usage is supported, this expansion would work as expected in match
>>>> and guard contexts as well, since it expands before variable references
>>>> are resolved:
>>>>
>>>>
>>>>
>>>> { :foo , baz} = & :foo
>>>>
>>>> # == { :foo , baz} = { :foo , foo}
>>>>
>>>> # => { :foo , 1 }
>>>>
>>>> baz
>>>>
>>>> # => 1
>>>>
>>>>
>>>>
>>>> *List Captures*
>>>>
>>>> **
>>>>
>>>> Since capture expressions are allowed in lists, this can be used to
>>>> construct Keyword lists from the local variable scope elegantly:
>>>>
>>>>
>>>>
>>>> list = [ & :foo , & :bar ]
>>>>
>>>> # == list = [{ :foo , foo}, { :bar , bar}]
>>>>
>>>> # => [ foo: 1 , bar: 2 ]
>>>>
>>>>
>>>>
>>>> This would work with other list operators like *|* :
>>>>
>>>>
>>>>
>>>> baz = 3
>>>>
>>>> list = [ & :baz | list]
>>>>
>>>> # == list = [ { :baz , baz} | list ]
>>>>
>>>> # => [ baz: 3 , foo: 1 , bar: 2 ]
>>>>
>>>>
>>>>
>>>> And list destructuring:
>>>>
>>>>
>>>>
>>>> {foo, bar, baz} = { nil , nil , nil }
>>>>
>>>> [ & :baz , & :foo , & :bar ] = list
>>>>
>>>> # == [{ :baz , baz}, { :foo , foo}, { :bar , bar}] = list
>>>>
>>>> # => [ baz: 3 , foo: 1 , bar: 2 ]
>>>>
>>>> {foo, bar, baz}
>>>>
>>>> # => { 1 , 2 , 3 }
>>>>
>>>>
>>>>
>>>> *Map Captures*
>>>>
>>>> **
>>>>
>>>> With a small change to the parser, (
>>>> https://github.com/elixir-lang/elixir/commit/0a4f5376c0f9b4db7d71514d05df6b8b6abc96a9
>>>> ) we can allow this expression inside map literals. Because this expression
>>>> individually gets expanded into a tagged-tuple before the map associations
>>>> list as a whole are processed, it allow this syntax to work in all
>>>> existing map/struct constructs, like map construction:
>>>>
>>>>
>>>>
>>>> map = %{ & :foo , & "bar" }
>>>>
>>>> # == %{ :foo => foo, "bar" => bar}
>>>>
>>>> # => %{ :foo => 1 , "bar" => 2 }
>>>>
>>>>
>>>>
>>>> Map updates:
>>>>
>>>>
>>>>
>>>> foo = 3
>>>>
>>>> map = %{map | & :foo }
>>>>
>>>> # == %{map | :foo => foo}
>>>>
>>>> # => %{ :foo => 3 , "bar" => 2 }
>>>>
>>>>
>>>>
>>>> And map destructuring:
>>>>
>>>>
>>>>
>>>> {foo, bar} = { nil , nil }
>>>>
>>>> %{ & :foo , & "bar" } = map
>>>>
>>>> # == %{ :foo => foo, "bar" => bar} = map
>>>>
>>>> # => %{ :foo => 3 , "bar" => 2 }
>>>>
>>>> {foo, bar}
>>>>
>>>> # => { 3 , 2 }
>>>>
>>>>
>>>>
>>>> *Considerations*
>>>>
>>>>
>>>>
>>>> Though just based on an errant thought (
>>>> https://groups.google.com/g/elixir-lang-core/c/oFbaOT7rTeU/m/BWF24zoAAgAJ
>>>> ) that popped into my head yesterday, I'm unreasonably pleased with how
>>>> well this works and reads in practice. I will present my thoughts here,
>>>> though again I encourage you to grab my branch (
>>>> https://github.com/christhekeele/elixir/tree/tagged-variable-capture ) ,
>>>> compile
>>>> it from source (
>>>> https://github.com/christhekeele/elixir/tree/tagged-variable-capture#compiling-from-source
>>>> ) , and play with it yourself!
>>>>
>>>>
>>>>
>>>> *Pro: solves existing pain points*
>>>>
>>>> **
>>>>
>>>> As mentioned, this solves flaws previous proposals suffer from:
>>>>
>>>> *
>>>> Atom vs String (
>>>> https://groups.google.com/g/elixir-lang-core/c/NoUo2gqQR3I/m/IpZQHbZk4xEJ
>>>> ) key support
>>>>
>>>> This supports both.
>>>>
>>>>
>>>> *
>>>> Visual clarity (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/NBkAVto0BAAJ
>>>> ) that atom/string matching is occurring
>>>>
>>>> This leverages the appropriate literal in question within the syntax
>>>> sugar.
>>>>
>>>>
>>>> *
>>>> Limitations of string-based sigil parsing (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/TiZw6xM3BAAJ
>>>> )
>>>>
>>>> This is compiler-expansion-native.
>>>>
>>>>
>>>> *
>>>> Easy confusion (
>>>> https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/WRhXxHDfBAAJ
>>>> ) with tuples
>>>>
>>>> %{&:foo, &"bar"} is very different from {foo, bar}, instead of 1-character
>>>> different.
>>>>
>>>>
>>>> Additionally, it solves my main complaint with historical proposals:
>>>> syntax to combine a variable identifier with a literal must either obscure
>>>> that we are building an identifier, or obscure the key/string typing of
>>>> the literal.
>>>>
>>>>
>>>>
>>>> I'm proposing overloading the capture operator rather than introducing a
>>>> new operator because the capture operator already has a semantic
>>>> association with messing with variable scope, via the nested integer-based
>>>> positional function argument syntax (ex *& &1* ).
>>>>
>>>>
>>>>
>>>> By using the capture operator we indicate that we are messing with an
>>>> identifier in scope, but via a literal atom/string we want to associate
>>>> with, to get the best of both worlds.
>>>>
>>>>
>>>>
>>>> *Pro: works with existing code*
>>>>
>>>> **
>>>>
>>>> The capture today operator has well-defined compile-time-error semantics if
>>>> you try to pass it an atom or a string. All compiling Elixir code today
>>>> will
>>>> continue to compile as before.
>>>>
>>>>
>>>>
>>>> *Pro: works with existing tooling*
>>>>
>>>> **
>>>>
>>>> By overloading an existing operator, this approach works seamlessly for me
>>>> with the syntax highlighters I have tried it with so far, and reasonable
>>>> with the formatter.
>>>>
>>>>
>>>>
>>>> In my experimentation I've found that the formatter wants to rewrite
>>>> *&:baz*
>>>> to *(&:baz)* pretty often. That's good, because there are several edge
>>>> cases in my prototype where not doing so causes it to behave strangely;
>>>> I'm sure it's resolving ambiguities that would occur in function captures
>>>> that impact my proposal in ways I have yet fully anticipated.
>>>>
>>>>
>>>>
>>>> *Pros: minimizes surface area of the language*
>>>>
>>>> **
>>>>
>>>> By overriding the capture operator instead of introducing a new operator
>>>> or sigil, we are able to keep the surface area of this feature slim.
>>>>
>>>>
>>>>
>>>> *Cons: overloads the capture operator*
>>>>
>>>> **
>>>>
>>>> Of course, much of the virtues of this proposal comes from overloading the
>>>> capture operator. But it is an already semantically fraught syntactic
>>>> sugar construct that causes confusion to newcomers, and this would place
>>>> more strain on it.
>>>>
>>>>
>>>>
>>>> We would need to augment it with more than the meager error message
>>>> modification (
>>>> https://github.com/elixir-lang/elixir/commit/3d83d21ada860d03cece8c6f90dbcf7bf9e737ec#diff-92b98063d1e86837fae15261896c265ab502b8d556141aaf1c34e67a3ef3717cL199-R207
>>>> ) in my prototype, as well as documentation and anticipate a new wave of
>>>> questions from the community upon release.
>>>>
>>>>
>>>>
>>>> This inelegance really shows when considering embedding a tagged variable
>>>> capture inside an anonymous function capture, ex *& &1 = &:foo*. In my
>>>> prototype I've chosen to allow this rather than error on "nested captures
>>>> not allowed" (would probably become: "nested function captures not
>>>> allowed"), but I'm not sure I found all the edge-cases of mixing them in
>>>> all possible constructions.
>>>>
>>>>
>>>>
>>>> Additionally, since my proposal now allows the capture operator as an
>>>> associative element inside map literal parsing, that would change the
>>>> syntax error reported by providing a function capture as an associative
>>>> element to be generated during expansion rather than during parsing. I am
>>>> not fluent enough in leex to have have updated the parser to preserve the
>>>> exact old error, but serendipitously what it reports in my prototype today
>>>> is pretty good regardless, but I prefer the old behaviour:
>>>>
>>>>
>>>>
>>>> Old:
>>>>
>>>> %{ & &1 }
>>>>
>>>> # !> ** (SyntaxError) syntax error before '}'
>>>>
>>>> # !> |
>>>>
>>>> # !> 1 | %{ & &1 }
>>>>
>>>> # !> | ^
>>>>
>>>> New:
>>>>
>>>> %{ & &1 }
>>>>
>>>> # => error: expected key-value pairs in a map, got: & &1
>>>>
>>>> # => ** (CompileError) cannot compile code (errors have been logged)
>>>>
>>>>
>>>>
>>>> *Cons: here there be dragons I cannot see*
>>>>
>>>> **
>>>>
>>>> I'm quite sure a full implementation would require a lot more knowledge of
>>>> the compiler than I am able to provide. For example, *&:foo = &:foo* raises
>>>> an exception where *(&:foo) = &:foo* behaves as expected. I also find the
>>>> variable/context/binding environment implementation in the erlang part of
>>>> the compiler during expansion to be impenetrable, and I'm sure my
>>>> prototype fails on edge cases there.
>>>>
>>>>
>>>>
>>>> *Open Question: the pin operator*
>>>>
>>>> **
>>>>
>>>> As this feature constructs a variable ref for you, it is not clear if/how
>>>> we should support attempts to pin the generated variable to avoid new
>>>> bindings. In my prototype, I have tried to support the pin operator via
>>>> the *&^:atom* syntax, though I'm pretty sure it's super buggy on bare
>>>> out-of-data-structure cases and I only got it far enough to work in
>>>> function heads for basic function head map pattern matching.
>>>>
>>>> **
>>>>
>>>> *Open Question: charlists* **
>>>>
>>>> **
>>>>
>>>> I did not add support for charlist tagged variable captures in my
>>>> prototype, as it would be more involved to differentiate a capture of list
>>>> mean to become a tagged tuple from a list representing the AST of a
>>>> function capture. I would not lose a lot of sleep over this.
>>>>
>>>> **
>>>>
>>>> *Open Question: allowed contexts*
>>>>
>>>>
>>>>
>>>> Would we even want to allow this syntax construct outside of map literals?
>>>> Or list literals?
>>>>
>>>>
>>>>
>>>> I can certainly see people abusing the
>>>> bare-outside-of-associative-datastructure syntax to make some neigh
>>>> impenetrable code where it's really unclear where assignment and pattern
>>>> matching is occuring, and relatedly this is where I see a lot of odd
>>>> edge-case behaviour in my prototype. I allowed it to speed up the
>>>> implementation, but it merits more discussion.
>>>>
>>>>
>>>>
>>>> On the other hand, this does seem like an... interesting use-case:
>>>>
>>>>
>>>>
>>>> error = "rate limit exceeded"
>>>>
>>>> & :error # return error tuple
>>>>
>>>>
>>>>
>>>> *Thanks for reading! What do you think?*
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>> --
>>>>
>>>> You received this message because you are subscribed to the Google Groups
>>>> "elixir-lang-core" group.
>>>>
>>>> To unsubscribe from this group and stop receiving emails from it, send an
>>>> email to elixir-lang-co... @ googlegroups. com.
>>>>
>>>> To view this discussion on the web visit https:/ / groups. google. com/ d/
>>>> msgid/ elixir-lang-core/
>>>> ad7e0313-4207-4cb7-a5f3-d824735830abn%40googlegroups.
>>>> com (
>>>> https://groups.google.com/d/msgid/elixir-lang-core/ad7e0313-4207-4cb7-a5f3-d824735830abn%40googlegroups.com?utm_medium=email&utm_source=footer
>>>> ).
>>>>
>>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>>
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "elixir-lang-core" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to elixir-lang-core+unsubscribe@ googlegroups. com (
>> elixir-lang-core+unsubscr...@googlegroups.com ).
>> To view this discussion on the web visit https:/ / groups. google. com/ d/
>> msgid/ elixir-lang-core/
>> 2b46232e-04f1-4b21-87e6-9c098741cd36n%40googlegroups.
>> com (
>> https://groups.google.com/d/msgid/elixir-lang-core/2b46232e-04f1-4b21-87e6-9c098741cd36n%40googlegroups.com?utm_medium=email&utm_source=footer
>> ).
>>
>
>
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to elixir-lang-core+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/ljgfhpbi.801a91e1-68bd-4433-b25f-3bec8f0b68a8%40we.are.superhuman.com.
