From: "dsisnero (Dominic Sisneros)" <noreply@...>
Date: 2022-11-03T21:38:24+00:00
Subject: [ruby-core:110597] [Ruby master Feature#19015] Language extension by a heredoc

Issue #19015 has been updated by dsisnero (Dominic Sisneros).


It reminds me of javascript template literals and tagged templates.  Instead of passing in bindings they pass the interpolation points and the first argument is an array containing thestring split at interpolation points, and the second is the interplation values.

``` ruby
require 'cgi'

def heredoc_extension_erb strs_separated_array_at, **interpolation_points
    result = strs_separated_array.zip(interpolation_points).each_with_object([]) do |s, v, ar|
         ar << s
         ar << v if v
   end
   result.join(" ")
end

name = 'ko1'

html = <<!html
<div class="#{clsname}">Hello #{name}</div>
erb
```

I could see where this could be used to provide cmd interpolation similar to julia
``` ruby
files = ["/etc/password", "/Volumes/External HD/data.csv"]

def heredoc_ext_cmd(strs_ar, values)
   # shellescape values - 
   # if current_values is a array and curr_str ends in space and next str is nonexistant or ends in space join values with a space
   # 
   #collect cmd and cmd_args
  result = Process.new(cmd, cmd_args)
end

mycmd = <<!cmd
  grep foo #{files}
cmd

mycmd.run
```




----------------------------------------
Feature #19015: Language extension by a heredoc
https://bugs.ruby-lang.org/issues/19015#change-99928

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
----------------------------------------
This propose new heredoc extension with `<<!LANG` like

```ruby
doc = <<!LANG
  # description written in lang LANG
  foo bar
LANG
```

and it is translated to:

```ruby
doc = heredoc_extension_LANG(heredoc_text, binding)
```

## Example

```ruby
require 'erb'

def heredoc_extension_erb str, b
  ERB.new(str).run(b)
end

name = 'ko1'

html = <<!erb
<div>Hello <%= name %></div>
erb

puts html #=> <div>Hello ko1</div>
```

## Background / considerations

* Sometimes we write Ruby syntax string with `<<RUBY` and this proposal inspired by it.
* it is similar to shebang (`#!LANG` in shell)
* [Elixir's custom sigil](https://elixir-lang.org/getting-started/sigils.html) translates `~u(...)` translates to `sigil_u(...)`. This is why it translated to `heredoc_extension_LANG(...)` private method call.
* JavaScript has JSX but I don't think it is fit to the Ruby language.
* Heredoc is Ruby's chaos part and already confusing a lot. Additional chaos doesn't matter.
* `<<!foo` is valid syntax but now I don't think it is not used. gem codesearch doesn't find the usage.
* Sorry I couldn't wait 1st/Apr.

## Implementation

I attached the experimental implementation which only supports `erb` (because I couldn't find how to get delimiter to determine a method name :p).


---Files--------------------------------
heredoc_extension.patch (2.7 KB)


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