On: Fantastic DSLs and where to find them

[pmontra]

You can have both mutability and immutability in the same language. Example from Ruby:

    $ irb
    2.4.1 :001 > a = [1, 2, 3]
     => [1, 2, 3] 
    2.4.1 :002 > a.map {|x| x + 1}
     => [2, 3, 4] 
    2.4.1 :003 > a
     => [1, 2, 3] 
    2.4.1 :004 > a.map! {|x| x + 1}
     => [2, 3, 4] 
    2.4.1 :005 > a
     => [2, 3, 4] 
    2.4.1 :006 > a.freeze # make a immutable
     => [2, 3, 4] 
    2.4.1 :007 > a.map! {|x| x + 1}
    RuntimeError: can't modify frozen Array

Ruby is fundamentally a language based on mutability, but it shows that it should be possible to have both ways. Questions:

1) Is really there a language which is fully agnostic about mutability and immutability?

2) If not, it's maybe because designers have strong opinions about this matter? Actually IMHO designing a fully agnostic language would demonstrate strong opinions too.

[moosingin3space → pmontra]

I'd argue most languages are agnostic about (im)mutability. It's libraries that aren't.

[pmontra → moosingin3space]

Most but some don't. This fails in Erlang

    X = X + 1.

because even variables are immutable.

This is ok in Elixir even if it kind of fakes it [1]

    x = x + 1

and it's perfectly ok in Ruby and most other languages.

[1] http://blog.plataformatec.com.br/2016/01/comparing-elixir-an...