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Comment by J-Kuhn | Hacker News Reader

If someone asks me of a small snippet that describes some fundamental thing about TCL, I will respond with this:

    set a puts
    $a "Hello World"

A command is just a list. Substitution is done before executing it. That's why [set] requires the variable name, not $variable.

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Python:

    a = print
    a("Hello World")

Rust:

    fn puts(s: &str) {
        println!("{}", s);
    }
    
    let a = puts;
    a("Hello World");

C++:

    #include <cstdio>

    auto a = puts;
    a("Hello World");

Also: every FP language ever. How is that a fundamental thing about TCL?

Also probably all shell scripting languages, like Bash:

    a=echo
    $a Hello World

The way I'm used to seeing the GP's example made is

    set a pu
    set b ts
    $a$b "Hello!"

which I think does a better job showing how the mixture of strings with interpolation allows for some slightly unexpected things.

Yes, you're probably right. Frankly, I'd rather not have this kind or error-prone behavior in my programming languages, not even when scripting. It makes proper handling of strings hard and cumbersome (as evidenced by a lot of software that can't handle spaces in file names because it's calling scripts written in sh or bash), and I don't get the Tcl love professed in the comments here.

I'm not a fan of Tcl -- I used it a bit in the 90's -- but this really isn't the best example. You need a bit more context to give it a fair shake.

This is kind of clumsy in R5RS Scheme:

    ((eval (string->symbol (string-append "dis" "play"))) "Hello world")

Good lord, as an example of why it's something we should want?

Each to their own of course, but..

I don't think this is the sort of code that people tend to write. But it does a good job of succinctly explaining how Tcl works.

For example because it's kind of homoiconic. Since everything is a string you can define your own control flow constructs for example...

If you define your own, say, repeat-until loop, can you use the built-in break and continue commands? Could you define a break-with-value command for the built-in loops?

Using Tcl exceptions, I guess it would be pretty trivial to do that.

Here [1] is an alternative do..while loop implementation provided by Tcllib, written in pure Tcl.

[1] https://core.tcl-lang.org/tcllib/artifact/4f7e97706ff67a40

Would it be fair to call this a kind of "pervasive eval"?

you've misspelled "evil" ;)

in TeX:

\def\a{mess}\def\b{age}\csname \a\b \endcsname {Hello there}\bye

in (UCB)LOGO:

? run list word "pri "nt [Hello there]

Because if you say a = "puts" in the other langs it wouldn't work. The other languages are assigning a function to a variable. Tcl is assigning a string to a variable, then evaluating the string as a function based on syntax.

Now do the same thing with 'if' and 'while'. In Tcl, you can define your own do...while loop.

In your examples, you need "types" to understand the code. In the parent TCL example, there is no type, thus, way simpler. Programming is a process, not just code and result. TCL process is way simpler.

If you use quoted strings in both lines, your intent will be more clear.

   set a "puts"
   $a "Hello World".

On the other hand, I have not used Tcl since the last time I run a Verilog on AIX (21 years ago). I don't miss it.

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