Category talk:Tcl

Temporary: Just so this is easy to find for now. Reports:Tasks not implemented in Tcl

Tasks Unlikely to get Implemented

This is a short discussion of the tasks that are marked with the omit template. —Dkf 09:14, 21 May 2009 (UTC)

Parametric Polymorphism: Tcl doesn't have static typing, making this task ridiculously trivial/non-applicable. Note also that the task itself states that it only applies to languages with static typing.
Constrained Genericity: This is a specialization of the Parametric Polymorphism task, so all comments there apply here too.

Language features

Tcl uses a mixture of pass-by-value and pass-by-reference, and is very good at simulating pass-by-name too. The base language semantics are strictly pass-by-value; this was how everything was done up to Tcl 7.6, and when combined with the fact that it was also string based, it gave the language a (deserved) reputation for being slow. In Tcl 8.0 the language implementation was switched to pass-by-reference, with the entities being semantically immutable objects (the actual code is more nuanced than that, of course); that was a major part of why Tcl sped up with that version. The pass-by-name support is through the upvar command, which allows the looking-up of a variable in one scope and aliasing it to another variable in the current scope. —Dkf 10:16, 31 May 2009 (UTC)

I've selected these features:

exec=bytecode

Tcl's used a bytecode engine (with occasional interpretation) since 8.0, i.e., 1996.

OK, we've been discussing compiling to native code for a while now, but we've not got the effort to make that viable across lots of platforms, and going to a common bytecode format like JVM, CIL or LLVM is awkward as they are much more low-level than Tcl; for example, Tcl's variables aren't just simple bits of memory but also have a lot of other things that can be attached off them. —Donal Fellows 08:23, 6 August 2009 (UTC)

expression=dynamic

We use dynamic typing in expr.

compat=duck

We say it's a ~~duck~~list if it supports the operations of a ~~duck~~list.

checking=dynamic

Our type checks are applied at runtime only. That's when they are enforced strictly.

parampass=value

We always pass parameters by value. We simulate pass-by-reference by passing handles/names and pass-by-name with the help of upvar.

safety=safe

The language, especially in a safe interpreter, has no unsafe operations at all.

paradigms=Imperative, Object-oriented, Event-driven, Reflective, Concurrent

Tcl supports all of these handily enough. With more detail/justification:

Concurrent: The Thread extension is long-established.
Event-driven: While Tk has always been event driven, Tcl has been since 7.5 or 7.6 when it gained the event loop from Tk.
Imperative: Tcl is definitely an imperative language.
OO: Tcl supports this through many extensions, and natively from 8.6.
Reflective: Tcl's had introspection for ages; it's vital for the language's self-tests.

We need to check whether these features are enough; if not, we should update the Language template... —Donal Fellows 12:26, 1 June 2009 (UTC)

How to use?

What is the correct command to start the examples? I tried 'tclsh' or 'wish', like

  $ tclsh <fileWithTheCode>'

but didn't succeed for many of the examples. I use version 8.4 under Debian Squeeze, and I'm aware that all those examples that need a higher version of Tcl won't run. But if I try, for example, the "GUI component interaction" task, I get

  invalid command name "ttk::frame"
     while executing
  "ttk::frame .bg"

If I try "Extend your language", I get

  missing close-bracket
     while compiling
  "set c1 [uplevel 1 [list expr $cond1]

What am I doing wrong? Is 'tclsh' the right command? --Abu 10:11, 27 August 2010 (UTC)

'tclsh' is most often the right command to run the Tcl interpreter. 'wish' is Tcl+Tk (the GUI toolkit), but you can as well add

  package require Tk

early in the script, which then can also be called with 'tclsh'.

"Extend your language" is buggy (brackets must be balanced) in

   set c1 [uplevel 1 [list expr $cond1]
   set c2 [uplevel 1 [list expr $cond2]

where a "]" is missing at the end of both lines. I think one should only paste tested code, and test again after editing it... -- Suchenwi (talk) 22:34, 30 January 2021 (UTC)