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

but you probably don't want to write your fractal renderer or real-time raytracer in tcl. by contrast, i've done both of those successfully in lua with luajit: https://gitlab.com/kragen/bubbleos/blob/master/yeso/mand.lua https://gitlab.com/kragen/bubbleos/-/blob/master/yeso/sdf.lu...

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