Category talk: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)
- Tcl's got a grammar, but it only works at the level of the base language syntax, and that's just not a level that Tclers think about that much. (For example, it doesn't tell you anything about
while, let alone that it has an embedded block of code.) It is also about as difficult to write down as reimplementing the Tcl parser in another language.
- This is a specialization of the Parametric Polymorphism task, so all comments there apply here too.
- Need the concept of proof in the language for this, and this is really an area that Tcl doesn't address. The formal way to fix it is to write a theorem prover in Tcl, but that'd be a ridiculous amount of work.
- 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.
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:
expression=dynamic
- We use dynamic typing in
expr.
compat=duck
- We say it's a
ducklist if it supports the operations of aducklist.
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)