'everything is a string' is a fatal flaw in tcl, both in terms of bugproneness and performance. it does have some real advantages, though: serialization for storage, configuration, debugging, or networking is trivial, and it eliminates aliasing bugs, especially important for end-user programming
independent of 'everything is a string', tcl also works much better as a command language than 'real programming languages' do; contrast
ifup eth0 -ip 192.168.2.53
with
ifup('eth0', ip='192.168.2.53')
which is a real pain to type when you're in a hurry. but you could get that benefit by only making things strings by default; requiring [] or $ to get expression evaluation is conceptually independent of tcl's type system or lack thereof
the rebol family seems like an improvement over conventional programming languages there, but at the cost of conceptual simplicity
wrt guis in particular the ability to edit the gui without restarting it is pretty great. but this is a suboptimal way to edit it:
.qd.ipentry configure -textvariable ip
on the other hand, the ability to trigger code when a variable changes is pretty awesome
Interesting example. Now I maybe understand a little what is meant with everything being a string. Before, I didn't quite know the catch.
Rebol went the opposite way for somewhat similar effect. It famously had (I think) 37 datatypes and a lot of them were also syntax types, like email, url, IP also I think. So your example could be something like this in Rebol:
"everything is a string" hasn't been a serious performance issue since the release of Tcl 8.0 decades ago. I've written large, successful applications in Tcl/Tk.
Granted, programming in the large in Tcl requires discipline and a good set of tools. (I used the Snit object framework, with SQLite as a data store.)
As for command languages: yes, this is where Tcl really shines; nothing else is as good.
tcl 8.6.13 still has serious performance problems, although indeed 8.0 did improve the situation dramatically; it's on the order of 64× slower than native code in simple microbenchmarks like http://canonical.org/~kragen/sw/dev3/dumbfib.tcl, which also means about 2× slower than cpython. its type system is a big part of the reason why
compare†:
: ~; time tclsh <<<'proc fib {n} { if {$n < 2} {return 1} else {return [expr {[fib [expr {$n - 1}]] + [fib [expr {$n - 2}]]}]}}; puts [fib 35]'
14930352
real 0m8.351s
user 0m8.346s
sys 0m0.004s
: ~; time luajit -e 'function fib(n) if n < 2 then return 1 else return fib(n-1) + fib(n-2) end end print(fib(35))'
14930352
real 0m0.127s
user 0m0.122s
sys 0m0.004s
even with the huge performance hacks added in tcl 8.0, it's only about 64 times faster than bash
: ~; time bash -c 'fib() { if [[ $1 -lt 2 ]]; then result=1; else local arg=$1; fib $(($arg - 1)); local tmp=$result; fib $(($arg - 2)); result=$(($tmp + $result)); fi; }; fib 35; echo "$result"'
14930352
real 8m24.591s
user 8m24.412s
sys 0m0.028s
which puts it about halfway in between shell scripts and native code
that doesn't mean you can't write large, successful applications in tcl, even without any c extensions! a core i7 is about 17000 dhrystone vax mips http://www.roylongbottom.org.uk/dhrystone%20results.htm while a pentium 166 was about 270 mips. so anything you could do with usable performance on a pentium you can do, with enough discipline, in pure tcl. it'll probably be a lot quicker to write than pentium assembly, too. and things like arrays (hash tables), regular expressions, sqlite, tk, etc., are of course enormously faster on a current computer, and you have a thousand times as much ram to play with and probably an ssd
in terms of command languages, what do you recommend for getting good tab-completion in tcl? i don't know of any good options but that doesn't mean there aren't any; it probably just means i'm ignorant
______
†before wduquette's very helpful correction, I had:
: ~; time tclsh <<<'proc fib {n} { if {$n < 2} {return 1} else {return [expr [fib [expr $n - 1]] + [fib [expr $n - 2]]]}}; puts [fib 35]'
14930352
real 0m59.757s
user 0m59.736s
sys 0m0.004s
and while, in some sense, maybe my additional 8× slowdown here was kind of a performance effect of the everything-is-a-string type system, it's not an unavoidable one
You can speed that Tcl snippet up considerably by putting braces around the expressions, e.g., `expr {$n - 1}`. On my system it went from ~22 seconds to ~4 seconds.
Without the braces, the expression gets parsed twice, once as Tcl syntax and once as Tcl `expr` syntax. Luajit is still going to be faster, but Tcl will do better than what you're showing there. (Not bracing expressions is the most common reason by why Tcl code runs slowly.)
In terms of tab-completion, you have to roll your own; and if you're trying to do it in the console, you're going to need to write your own REPL: the standard `tclsh` doesn't even have "readline" editing.
Back when I was doing Tcl regularly, I wrote a Tk "terminal" widget, and all my Tcl/Tk apps had a way to pop it up. Made life much easier.
hey, thanks! i should have known that and didn't. i've corrected my comment above since you corrected me so quickly that i could still edit it!
i feel like readline and tab-completion is pretty important to a good command language, and plausibly you want to integrate support for tab-completion into the design of the language itself rather than having to write a separate completer for each command
i'm kind of puzzled why tclsh doesn't have any command-line editing. maybe ousterhout's team was only ever using tclsh in emacs shell-mode or something like your tk terminal? as an exercise, i wrote a basic command-line editor in c in bed on my cellphone the other night. it took me an hour and a half and 120 lines of code (with a very narrow line length to fit onto the cellphone screen), and it supports arrow keys, movement by words, word delete, about a dozen keystroke commands in all, which is most of the ones i use. (though i really need to fix the cbreak handling and handling of wide lines to work reliably.)
Historically it’s because TCL uses the BSD license and GNU readline does not. But yeah, no reason not to implement an alternative.
As for speed, it’s less that everything is a string (internally, data gets stored as both a string and whatever it last needed to be converted to) and more because TCL is so dynamic that compiling it is hard.
There’s been some work on compiling to native though.
upvar and uplevel are a significant barrier to optimisation, but not to plain compilation — the hardest part would be autovivification of fresh up-locals, and even that sounds like an extra indirection could reasonably handle it?
EDIT: looks like tcl doesn't bytecode uplevel expressions, so I must be missing a catch?
yeah, what i was thinking of specifically was that they would be a major barrier to optimization, which is the benefit one hopes for from compilation
to be specific, it would be pretty hard to optimize a non-leaf procedure if any other procedure it called were able to violate any assumptions you'd made when optimizing it. elided redundant type checks, perhaps to specialize a proc? the proc it called changed the type of one of its variables. constant propagation? that proc changed the value of the variable you thought was constant. strength-reduction? likewise. you aren't going to get much dead code elimination without constant propagation. invariant hoisting? how are you going to figure out what's invariant if a proc you're calling inside the loop could change any of the variables used in it? register allocation? better have a way for upvar and uplevel to look up which register it was
tcl's string interpolation semantics are much, much better than unix shell semantics, and i don't remember having seen a tcl string interpolation vulnerability along the lines of shell injection attacks and sql injection attacks and xss. still, it does seem like something to watch out for
independent of 'everything is a string', tcl also works much better as a command language than 'real programming languages' do; contrast
with which is a real pain to type when you're in a hurry. but you could get that benefit by only making things strings by default; requiring [] or $ to get expression evaluation is conceptually independent of tcl's type system or lack thereofthe rebol family seems like an improvement over conventional programming languages there, but at the cost of conceptual simplicity
wrt guis in particular the ability to edit the gui without restarting it is pretty great. but this is a suboptimal way to edit it:
on the other hand, the ability to trigger code when a variable changes is pretty awesome(edited to clarify)