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Comment by btilly | Hacker News Reader

Dynamic scope is supported in older Lisps (eLisp is the only widely used variant with it), and a variety of scripting languages including PHP, Perl, TCL and vimsh (that's vim's internal scripting language). It is rarish because it has been recognized as a bad design, but it still turns up because it is easy to implement.

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It is often recognized as bad design - though I don't think that's always fair. I thought of this because I was just reading some Java code that passed around a context object with all kinds of random things stuffed into it. It was, in effect, a way of simulating dynamic scope. There's a time and a place for everything. I'm sure dynamic scope can be horribly abused, but it's also nice to have in the toolbox for when you actually need to do what it does.

> eLisp is the only widely used variant with it

I think you mean it's the only widely used variant where it's the default. It's available in CL and Clojure when you want (need?) it.

And Haskell:

   import Control.Monad.Reader

    type Action = ReaderT String IO ()

    foo :: Action
    foo = do
      bar
      local (const "new state") bar
      bar

    bar :: Action
    bar = liftIO . putStrLn =<< ask

    > runReaderT foo "foo"
    foo
    new state
    foo

As well as scheme.

How does tcl, php, and vimscript support dynamic scoping? Examples please.

IIRC common lisp supports dynamic scoping too -- it defaults to lexical scoping though.

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