3 ms·

I'm not sure I understand your sentence (did you mean language x does implement dynamic scope?), but I feel obliged to mention Perl offers lexical scoping as we

• aerique 16y ago
  If you're a lazy language designer dynamic scope sort of emerges from the design proces while one really has to do extra work to support lexical scoping in a language.
• kragen 16y ago
  Perl 5 has dynamic scoping for backward compatibility with Perl 4, which had only dynamic scoping, and not only that, it botched it so that this code didn't work right: sub greet { local ($who) = @_; print "hello, $who\n"; } $who = "world"; &greet($who); This would print, "hello, " with a newline, due to a design bug called "variable suicide", which has been fixed in newer Perls. Needless to say, this made the extract-subroutine refactoring quite a bit more trouble in Perl 4.
  • avar 16y ago
    It doesn't just have it for backwards compatibility, it's still a very useful feature in some cases: sub foo { local $ENV{HOME} = "/foo/bar"; Code::I::Don't::Own(); } foo(); Having dynamic scope here ensures that the foreign code will use the environment I want without me having to alter it.
  • draegtun 16y ago
    Perl 6 also has dynamic scoping. But I don't think they kept it just for backward compatibility with Perl 4 & 5 :) Here is another example where dynamic scoping can indeed be very useful: sub bar { 'bar' } sub baz { bar() } sub foo { no warnings 'redefine'; local *bar = sub { 'My Bar' }; baz(); } say foo(); # => 'My Bar' say baz(); # => 'bar'