Join converts a Tcl list into a string. It glues together the elements of a list using a supplied string as element separator. Default is a space. For example:
% join {a b c} " and "
a and b and c
% join {a b c} ""
abcRS A typical application is to process a text that consists of several lines:
Matrices are a frequent application for nested lists. Here's a simple matrix summer that uses join twice: once for concatenating the rows; then for putting + signs in between so expr has something to parse:
foreach line [split $input \n] {
# do something with line, produce output
lappend outlines $out
}
set result [join $outlines \n]Another is to flatten out one level of embedded lists: % join {1 {2 {3 4}} 5}
1 2 {3 4} 5Lars H: As of Tcl 8.5, a more kosher way of doing that would be concat {*}$nestedListe.g. (yes, it looks silly) % concat {*}{1 {2 {3 4}} 5}
1 2 {3 4} 5The difference is that concat can return a list (something internally stored as a list), whereas join always returns a string, resulting in shimmering.Matrices are a frequent application for nested lists. Here's a simple matrix summer that uses join twice: once for concatenating the rows; then for putting + signs in between so expr has something to parse:
proc matsum matrix {expr [join [join $matrix] +]}
