4 ms·

I just guess there are two kinds of people in the world. I think scope leakage across logical boundaries is dangerous and really hurts maintainability and code

I just guess there are two kinds of people in the world. I think scope leakage across logical boundaries is dangerous and really hurts maintainability and code readability, and I think Tcl's tight restriction of variable scope by default is one of its most valuable properties. I'm so old I remember many conversations among perl and JavaScript programmers talking about the bug that drove them craziest, and it always seemed to come down to unexpected scope leakage and variable name collisions. Then there would be a lot of laughing and back-slapping and calls of 'been there bro!' I just can't wrap my head around that viewpoint. Better IMO to allow scope to cross function point boundaries only at well-defined points. I've been programming in Tcl for over 20 years and the times when use of upvar was called for have been very few. Meanwhile, how much of your code that you wrote 20 years ago still runs just fine on the latest tool stack?

bitwize 5y ago
I don't think that downward capture of bindings from an enclosing scope counts as "leakage" and I've never seen it lead to the maintainability issues you describe. In Perl and JavaScript, under certain conditions variable scope can leak upward, and that opens up its own can of fresh hell. Lexical scope also allows the lambda calculus to work, and with it powerful constructs like parameterized functions over values, and fine-grained restriction of variable access through lexical closures. An eager young Scheme programmer can write a module or object system for Scheme in an afternoon. Tcl allows those things to be written, but they're a bit more involved. And you have to exercise caution, as which bindings are live when a particular Tcl script gets executed is not clear from the program text. (I believe Tcl with upvar actually has dynamic scope semantics which, yet again, can of hell.) But hey, it's a wonderful thing that Tcl admits as much metaprogramming as it does, that puts it well ahead of many popular languages.

bitwize 5y ago

I don't think that downward capture of bindings from an enclosing scope counts as "leakage" and I've never seen it lead to the maintainability issues you describe. In Perl and JavaScript, under certain conditions variable scope can leak upward, and that opens up its own can of fresh hell. Lexical scope also allows the lambda calculus to work, and with it powerful constructs like parameterized functions over values, and fine-grained restriction of variable access through lexical closures. An eager young Scheme programmer can write a module or object system for Scheme in an afternoon. Tcl allows those things to be written, but they're a bit more involved. And you have to exercise caution, as which bindings are live when a particular Tcl script gets executed is not clear from the program text. (I believe Tcl with upvar actually has dynamic scope semantics which, yet again, can of hell.) But hey, it's a wonderful thing that Tcl admits as much metaprogramming as it does, that puts it well ahead of many popular languages.