Closures in Tcl

thesz

  > Well, I've encountered this use case a few times in Lisp:...
  > ...where a callback is used to collect various items.

This can be and is achieved by simple SQL-like query. Filter (flat) set of nodes by integerness and you even do not need a push_back.

Despite that, I find article interesting. It shows that Tcl can truely be multiparadigm programming language.

Myself, I've implemented pattern matching [1] over algebraic-type-like values and used that here and there.

[1] https://wiki.tcl-lang.org/page/Algebraic+Types

BoingBoomTschak

The callback way is more generic and prevents consing when you don't need to store the resulting node list. You may want to simply print something or maybe modify the node in-place, for example.

tialaramex

> In C++, this could be achieved if all local variables were in fact std::shared_ptr captured by value.

So, in C++ you do actually get to pick what happens and there are plenty of options but for our purposes here all we want is a (mutable) reference capture.

However, experienced C++ programmers would never do this because C++ is all foot guns all the time, so you can express what you meant and it'll blow up and cause chaos because now our reference outlives the thing referred to. Oops.

In Rust we can write what we meant, but instead of the program exploding at runtime the compiler will politely point out that this can't work and why.

And so armed with the knowledge from that, we can (in Rust or with C++ although it's harder to spell in C++) write something that'll actually work.

We could move the captured variable. In Rust we just use the keyword `move`, now the captured variable is gone, moved inside the closure, and so as with the Tcl the same variable (the one moved into this closure) is used each time the closure is called, and if we make another closure that's got a different captured variable.

But we could do the "shared reference" trick, that type is spelled Rc in Rust.

RHSeeger

> You might wonder why you'd ever need such a strange behaviour, right?

Closures can also be used to return a group of methods that all act on the same set of variables; ie, objects.

gitroom

Pretty cool seeing folks show up about Tcl, tbh I messed with it ages ago and never thought people were still this into it

RHSeeger

I don't get to use Tcl at work anymore, but I adore it. I use it for command line stuff on a regular basis

dingnuts

Is Tcl having a revival? Anybody know where Tclers hang out online?

pjmlp

I worked on a startup whose main language was Tcl, between 1999 and 2002, since then I hardly touched Tcl again.

Yet it has a special place on my heart and was one of the interpreters easiest to extend, in regards to the FFI API.

mhd

The Wiki[1] is one of the primary "hang out" spots, although it's a bit different from usual online communication. But there's a lot of mutual commenting, small articles and utilities etc. on there.

[1]: https://wiki.tcl-lang.org or https://wiki.tcl.tk

ofrzeta

"The European OpenACS and TCL/Tk conference will be in Bologna/Italy/Europe on July 10 & 11 2025." - this is crazy. Seems there are still people using OpenACS in 2025.

f1shy

If you work with VHDL or Verilog tools, it is very well alive and kicking. Forums about HDLs are full of it.

7thaccount

They did have a recent language update after awhile. That may have triggered some folks to look into it again. There is sometimes a HN effect where an initial post triggers some interest amongst enough users to get us new posts for a few weeks and then things tend to die off again. I've seen this with a lot of the more obscure languages like APL.

It would be cool to have a Tcl revival though (although I don't see it happening - I'm not in the community though so hopefully someone more informed can post). The language itself seems more capable than most give it credit for. I'm more of a Python fan myself, but can appreciate Tcl after reading through a book on it and writing a few scripts.

bandoti

I highly recommend The Tcl Programming Language: A Comprehensive Guide:

https://www.magicsplat.com/ttpl/index.html

For those who are not aware, Tcl is actually part of standard Python distribution through TKinter.

There are many things Tcl has built in that are quite amazing, like a robust virtual filesystem support, reflective channels, and less known these days Starpacks (stand alone runtime) that bundle sources with the binary.

I am current working on bringing back kitcreator for an AI project that uses Tcl as a scripting environment over llama.cpp.

https://github.com/tclmonster/kitcreator

Roy Keene is the original author, and has done some really clever stuff here, like encrypting the VFS appended to the executable. I added compression to this. It provides some manner of obfuscating sources.

And actually, I am also working on using tohil to compile a static Python and load it as a Tcl extension, with the goal to have standalone Python applications bundled with their sources and completely loadable from within the VFS. This will provide a means to bundle TKinter with a “frozen” Python app.

https://github.com/tclmonster/tohil

7thaccount

The previous edition of that book is the one I read lol. A great book. You can really feel the author's love of the language.

msephton

I last got help on the IRC channel (bridged to Slack, because I don't know IRC).

In the most recent big version update there was what I'd consider a breaking change regarding text encoding handling, but it was possible to go back to the old behaviour with an additional parameter .

null

[deleted]

IshKebab

It is unfortunately entrenched in the EDA industry. I have absolutely no idea why you would use it if you don't work in that space.

sokoloff

Because it works.

I introduced it into some of our release tooling in the mid-2000s. Easy to integrate, easy to understand, unsurprisingly good string/text handling, expect was very useful, and it’s not going to be used by anyone else, so no worries about version conflicts.

It ran successfully largely unchanged for around a decade.

IshKebab

Everything works. PHP works. Perl works. Bash works.

I like to use tools that more than merely work.

There's a reason nobody outside EDA uses it.

johnnyjeans

it's a language that's trivial to implement because it's well designed and simple, it embeds very nicely, and it's fantastic for use as a debug shell and to implement guis. it's a great technician's language, if you work with technically-minded people who aren't necessarily programmers, it's a great way to hand them deep interactive power without the footguns of a forth.

IshKebab

I would say it's cleverly designed. Well designed? Hmm, would a well designed language have such a basic flaw as comments that can only be used in very specific places?

monetus

r/TCL is worth a mention