From: "ko1 (Koichi Sasada)" <noreply@...>
Date: 2022-09-22T17:56:11+00:00
Subject: [ruby-core:109998] [Ruby master Feature#19015] Language extension by a heredoc

Issue #19015 has been updated by ko1 (Koichi Sasada).


This is tiny sample of SQL.
Note that I'm newbe of SQL (I goooooooogled the syntax/api and the example is never tested).

```ruby
module SQLite3HeredocExtension
  def compile str
    vs = []
    compiled = str.gsub(/\?([a-z_][a-zA-Z\d]+)/){|m|
      vs << $1
      ??
    }
    [vs, compiled]
  end

  # syntax
  # * SQL statement
  # * but ?var is replaced with the Ruby's variable

  def heredoc_exntesion_SQL str, b
    vs, compiled_str = compile str
    stmt = @db.prepare compiled_str
    @db.execute stmt, vs.map{|v| b.local_variable_get(v).to_s}
  end
end

require 'sqlite3'

@db = SQLite3::Database.new "test.db"
include SQLite3HeredocExtension

results = <<!SQL
  select person.name from people where person.age > ?lowest_age
SQL

## hmm, "SQL" seems to return a SQL statement...?

# AR
results = People.select(:name).where("age >= ?", lowest_age)

# AR/execute
results = ActiveRecord::Base.connection.execute("select person.name from perople where person.age > ?", lowest_age)
```


----------------------------------------
Feature #19015: Language extension by a heredoc
https://bugs.ruby-lang.org/issues/19015#change-99249

* 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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