How to match the variable in switch with contents of a list? - list

Question

I have a doubt concerning the use of switch in tcl. Mainly, I was wondering if it was possible to make something like:
switch myvar {
list1 {
puts "myvar matches contents of list1"; }
list2 {
puts "myvar matches contents of list2"; }
default {
puts "myvar doesn't match any content of any list"; }
}
In here, list1 and list2 would be either a list or array of strings containing the names of different files.
Is this even possible without making a very detailed regexp search?
Thanks!

Answer 1

You can rewrite it as an if elseif else construct easily, as Brian Fenton already said (and simplify it with the 'in' operator too.
if {$myvar in $list1} {
puts "myvar matches content of list"
} elseif {$myvar in $list2} {
puts "myvar matches content of list2"
} elseif {
puts "myvar doesn't match any content of any list"
}
You could of course wrap up the code and write your own switch version that does what you want, after all, this is Tcl...
proc listswitch {item conditions} {
if {[llength $conditions] % 2} {
return -code error "Conditions must be pairs"
}
set code ""
foreach {cond block} $conditions {
if {$cond eq "default"} {
set code $block
break
} elseif {$item in $cond} {
set code $block
break
}
}
if {$code ne ""} {
uplevel 1 $code
}
}
listswitch 10 {
{10 20 30 50} {
puts "Match in list 1" }
{50 20 90 11} {
puts "Match in list 2"
}
default {
puts "No match"
}
}
You need to worry a little if you want to match filenames literally, or what kind of equality your interested in though. There are some subtle things there, like case insensitive filesystems, different directory separators, absolute vs. relative and even stuff like filesystem encodings which might change the outcome.

Answer 2

Nice question Jason. At first, I thought you wanted a way to compare the contents of two lists. But I think you want to check if the string is a member of the lists. I don't see any easy way to do that with switch, so what I would do is very simply to use lsearch.
if {[lsearch $list1 $myvar ] != -1} {
puts "myvar matches contents of list1"; }
} elseif {[lsearch $list2 $myvar ] != -1} {
puts "myvar matches contents of list2"; }
} else
puts "myvar doesn't match any content of any list"; }
}