Can anyone explain me [list source file]?

list, tcl

Solution

That would appear to be using `list` to do command-script construction. I'd bet that the result of that `[list source file]` is then used with `uplevel` or `namespace eval`. Or possibly even `interp eval`.

The `list` command makes lists. It also makes substitution-free commands, so that:

eval [list $a $b]

is effectively identical in behaviour to:

$a $b

In your case, we have `source` instead of `$a` and `file` (which I'd lay strong odds on not being that literal) instead of `$b`. Why would we do this? Well, it ensures that if the file name has Tcl meta-characters in it (e.g., `{`) then the created script to source the file in won't have any problems at all when evaluated.

Why wouldn't you just write `source file` directly? Well, the most likely cases are where you want to `source` into a context other than the current one; the `source` command reads the file into a string and then effectively does an immediate `eval` on that string (well, there's some nuances, but it's surprisingly close to that). In particular:

proc foo {} {
    source bar.tcl
}

Will run the contents of `bar.tcl` inside the procedure body of foo, just as if you'd typed the text in there directly. The variables will be local variables (unless you use `global` or something like that) and so on. Most people don't write Tcl scripts that like that sort of treatment, frankly; to handle this, and make the code evaluate in a defined context, you'd actually write:

proc foo {} {
    # Quoted to defeat the Stack Overflow syntax highlighter only!
    uplevel "#0" [list source bar.tcl]
}

Problem

Original source