The above is how we dealt with undefined variable references until recently
(I think 1.15?): warn about the problematic expansion, error on the
expanded syntax.
On Wednesday, June 28, 2023 at 11:05:00 PM UTC-5 Christopher Keele wrote:
> An alternative would be to prepend compiler issues with a depiction of the
> how the sugar expands. Something like:
>
> %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz, $:baz}
> # !> warning: expanding %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz, $
> :baz} into a syntactically invalid construct:
> # !> %{:foo => foo, "fizz" => "buzz", "bar" => bar, fizz: :buzz, :baz =>
> baz}
> # !> iex:12:47
> # !> # !> ** (SyntaxError) invalid syntax found on iex:12:47:
> # !> ┌─ error: iex:12:47
> # !> 12 │ %{:foo => foo, "fizz" => "buzz", "bar" => bar, fizz: :buzz,
> :baz => baz}
> # !> │ ^
> # !> │
> # !> unexpected expression after keyword list. Keyword lists must
> always come last in lists and maps.
> # !>
> # !> Syntax error after: ','
>
> On Wednesday, June 28, 2023 at 10:56:13 PM UTC-5 Christopher Keele wrote:
>
>> %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz, $:baz}
>>
>> Personally, my preference would be to disallow this usage, but perhaps
>> with an even more instructive compiler error message.
>>
>> In fact, I think that we could leverage most existing errors/warnings
>> today, as long as things like the compiler error reporter desugar this
>> feature before reporting, to make it clearer upon error what is actually
>> going on in a variety of circumstances. This would give us something more
>> like:
>>
>> %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz, $:baz} # !> **
>> (SyntaxError) invalid syntax found on iex:12:47:
>> # !> ┌─ error: iex:12:47
>> # !> │
>> # !> 12 │ %{:foo => foo, "fizz" => "buzz", "bar" => bar, fizz: :buzz,
>> :baz => baz}
>> # !> │ ^
>> # !> │
>> # !> unexpected expression after keyword list. Keyword lists must
>> always come last in lists and maps.
>> # !>
>> # !> Syntax error after: ','
>> On Wednesday, June 28, 2023 at 10:44:44 PM UTC-5 Christopher Keele wrote:
>>
>>> Posted that last reply early. continued:
>>>
>>> Part of the elegance in of making $:foo and &"bar" expand to a valid
>>> pair, right before Map expansion handles pairs as {:%{}, [], [...pairs]},
>>> is that it *could* easily allow us to support mixing tagged variable
>>> captures anywhere in the existing syntax constructs: This is not true of my
>>> prototype today, though, it would need more work based on how we decide to
>>> handle it:
>>>
>>> {foo, bar, baz} = {1, 2, 3}
>>>
>>> %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz}
>>> # => %{:fizz => :buzz, :foo => 1, "bar" => 2, "fizz" => "buzz"}
>>>
>>> %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz, $:baz} # !> **
>>> (SyntaxError) invalid syntax found on iex:12:47:
>>> # !> ┌─ error: iex:12:47
>>> # !> │
>>> # !> 12 │ %{$:foo, "fizz" => "buzz", $"bar", fizz: :buzz, $:baz}
>>> # !> │ ^
>>> # !> │
>>> # !> unexpected expression after keyword list. Keyword lists must
>>> always come last in lists and maps. Therefore, this is not allowed:
>>> # !>
>>> # !> [some: :value, :another]
>>> # !> %{some: :value, another => value}
>>> # !>
>>> # !> Instead, reorder it to be the last entry:
>>> # !>
>>> # !> [:another, some: :value]
>>> # !> %{another => value, some: :value}
>>> # !>
>>> # !> Syntax error after: ','
>>>
>>>
>>>
>>> On Wednesday, June 28, 2023 at 10:32:20 PM UTC-5 Christopher Keele wrote:
>>>
>>>> > Alternatively, the `$` symbol could be used at the beginning of the
>>>> data structure to indicate that it is performing capture destructuring
>>>> (e.g., `$%{key1:, key2:}` or `$%{"key1", "key2"}`, but then it starts
>>>> feeling a little more line-noisy.
>>>>
>>>> I agree that'd be noisy. Also, it might make mixing tagged variable
>>>> literals, literal => pairs, and trailing keyword pairs even more confusing.
>>>>
>>>> Consider today that we support:
>>>> %{"fizz" => "buzz", foo: :bar}
>>>> # => %{:foo => :bar, "fizz" => "buzz"}
>>>>
>>>> But do not support:
>>>> %{foo: :bar, "fizz" => "buzz"}
>>>> # !> ** (SyntaxError) invalid syntax found on iex:5:12:
>>>> # !> ┌─ error: iex:5:12
>>>> # !> │
>>>> # !> 5 │ %{foo: :bar, "fizz" => "buzz"}
>>>> # !> │ ^
>>>> # !> │
>>>> # !> unexpected expression after keyword list. Keyword lists must
>>>> always come last in lists and maps. Therefore, this is not allowed:
>>>> # !>
>>>> # !> [some: :value, :another]
>>>> # !> %{some: :value, another => value}
>>>> # !>
>>>> # !> Instead, reorder it to be the last entry:
>>>> # !>
>>>> # !> [:another, some: :value]
>>>> # !> %{another => value, some: :value}
>>>> # !>
>>>> # !> Syntax error after: ','
>>>>
>>>> Supporting $%{key1:, key2:} or $%{"key1", "key2"} obfuscates this
>>>> situation even further.
>>>> On Wednesday, June 28, 2023 at 10:16:10 PM UTC-5 halos...@gmail.com
>>>> wrote:
>>>>
>>>>> On Wed, Jun 28, 2023 at 8:41 PM Paul Schoenfelder <
>>>>> paulscho...@fastmail.com> wrote:
>>>>>
>>>>>> I have an almost visceral reaction to the use of capture syntax for
>>>>>> this though, and I don’t believe any of the languages you mentioned that
>>>>>> support field punning do so in this fashion. They all use a similar
>>>>>> intuitive syntax where the variable matches the field name, and they
>>>>>> don’t
>>>>>> make any effort to support string keys.
>>>>>>
>>>>>
>>>>> JavaScript *only* supports string keys. Ruby’s pattern matching which
>>>>> can lead to field punning only supports symbol keys, but since ~2.2 Ruby
>>>>> can garbage collect symbols, making it *somewhat* less dangerous to
>>>>> do `JSON.parse!(data, keys: :symbol)` than it was previously.
>>>>>
>>>>> As far as I know, the BEAM does not do any atom garbage collection,
>>>>> and supporting *only* symbols will lead to a greater chance of atom
>>>>> exhaustion because a non-flagged mechanism here that only works on atom
>>>>> keys will lead to `Jason.parse(data, keys: :atom)` (and not
>>>>> `Jason.parse(data, keys: :atom!)`). I do not think that any destructuring
>>>>> syntax which works on maps with symbol keys but not string keys will be
>>>>> acceptable, although if it is constrained to *only* work on structs, then
>>>>> it does not matter (as that is the same restriction that it appears that
>>>>> OCaml and Haskell have).
>>>>>
>>>>> I think that either `&:key` / `&"key"` or `$:key` / `$"key"` will work
>>>>> very nicely for this feature, although it would be nice to have `&key:`
>>>>> or
>>>>> `$key:` work the same as the former version. Alternatively, the `$`
>>>>> symbol
>>>>> could be used at the beginning of the data structure to indicate that it
>>>>> is
>>>>> performing capture destructuring (e.g., `$%{key1:, key2:}` or `$%{"key1",
>>>>> "key2"}`, but then it starts feeling a little more line-noisy.
>>>>>
>>>>> I think that the proposal here — either using `&` or `$` — is entirely
>>>>> workable and IMO extends the concept nicely.
>>>>>
>>>>> -a
>>>>>
>>>>> 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:
>>>>>>
>>>>>> 1. Atom vs String
>>>>>>
>>>>>> <https://groups.google.com/g/elixir-lang-core/c/NoUo2gqQR3I/m/IpZQHbZk4xEJ>
>>>>>>
>>>>>> key support
>>>>>> 2. Visual clarity
>>>>>>
>>>>>> <https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/NBkAVto0BAAJ>
>>>>>>
>>>>>> that atom/string matching is occurring
>>>>>> 3. Limitations of string-based sigil parsing
>>>>>>
>>>>>> <https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/TiZw6xM3BAAJ>
>>>>>> 4. 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:
>>>>>>
>>>>>> 1. Atom vs String
>>>>>>
>>>>>> <https://groups.google.com/g/elixir-lang-core/c/NoUo2gqQR3I/m/IpZQHbZk4xEJ>
>>>>>> key
>>>>>> support
>>>>>> This supports both.
>>>>>> 2. 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.
>>>>>> 3. Limitations of string-based sigil parsing
>>>>>>
>>>>>> <https://groups.google.com/g/elixir-lang-core/c/XxnrGgZsyVc/m/TiZw6xM3BAAJ>
>>>>>> This is compiler-expansion-native.
>>>>>> 4. 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-co...@googlegroups.com.
>>>>>>
>>>>> To view this discussion on the web visit
>>>>>> https://groups.google.com/d/msgid/elixir-lang-core/4ee25f02-f27e-47a8-b4b5-b8520c1c9b05%40app.fastmail.com
>>>>>>
>>>>>> <https://groups.google.com/d/msgid/elixir-lang-core/4ee25f02-f27e-47a8-b4b5-b8520c1c9b05%40app.fastmail.com?utm_medium=email&utm_source=footer>
>>>>>> .
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Austin Ziegler • halos...@gmail.com • aus...@halostatue.ca
>>>>> http://www.halostatue.ca/ • http://twitter.com/halostatue
>>>>>
>>>>
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