[dbohdan] 2014-07-24: I haven't found discussions on the matter on the
wiki, so I made this page.

What do you guys think of the following style of indentation for 
functional-leaning Tcl code?

======
# style #1
return [
    join [
        ltrim [
            struct::list mapfor x $msgLines {string range $x $indent end}
        ]
    ] "\n"
]
======

Its main benefit over [Lisp%|%"Lispish"] indentation like

======
# style #2
return \
  [join \
    [ltrim \
      [struct::list mapfor x $msgLines {string range $x $indent end}]] "\n"]
======

or


======
# style #3
return [join \
    [ltrim \
        [struct::list mapfor x $msgLines {string range $x $indent end}]] "\n"]
======

is that it doesn't break when a backslash at the end of a line goes missing.
The respective downside is that when you can't tell whether a command at the
beginning of the line is being quoted or substituted from just looking at it;
you have to see whether the line above it ends with a `[` or a `{`.

On a related note, have you programmed your text editor to manage the
backslashes within square brackets for the second/third style of
indentation? I'm considering doing that but it still seems brittle:
insert one newline in another editor (e.g., vi on the command line)
and it breaks.

An rather more ugly example:

======
# style #1
set conn [
    ::ftp::Open [
        dict get $websiteConfig deployFtpServer
    ] [
        dict get $websiteConfig deployFtpUser
    ] [
        dict get $websiteConfig deployFtpPassword
    ] -port [
        dict-default-get 21 $websiteConfig deployFtpPort
    ] -mode passive
]
======

vs.

======
# style #3
set conn [::ftp::Open \
    [dict get $websiteConfig deployFtpServer] \
    [dict get $websiteConfig deployFtpUser] \
    [dict get $websiteConfig deployFtpPassword] \
    -port [dict-default-get 21 $websiteConfig deployFtpPort] \
    -mode passive]
======

----
[aspect] - vote #1 for me.  I hate line-continuation backslashes and will try to avoid them wherever possible.  The difficulty distinguishing bracket-continuations from brace-continuations hasn't proven a problem for me - I think mostly because deeply nested code isn't particularly fun in Tcl under normal circumstances.

Your last example (style #3) invokes another situation where I will use continuation backslashes though:  calling a procedure with lots of arguments.  In this case I'll double-indent the arguments, which seems to be advocated in the [Tcl Style Guide]:
======
$w configure \
        -label [dict get $state what_it_is_called] \
        -command [lambda {} {puts "Hello, world!"}] \
        -otherattribute some-really-long-continued-value \
;# end $w configure
======
Note the comment at the end - that's a flourish of my own (?) which I add so the argument lines can be freely rearranged without the risk of forgetting to remove the last \.

And I think [struct::list mapfor] is obsoleted by [lmap] -- if not, I'd [interp alias] it to a less ugly name for common use :-).

[dzach] 2014-7-27 : One other useful aspect of the proposed style, when used in a [proc], is that it preserves the white space, including line feeds, when doing ''[[info body]'', thus allowing the regeneration of the initial appearance of a [proc] during an introspection.
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