variables/arrays from tcl procedure - variables

Question

How could i pass some variables/ arrays outside of procedure?
Lets say I've my procedure 'myproc' with inputparameters {a b c d e}, e.g.
myproc {a b c d e} {
... do something
(calculate arrays, lists and new variables)
}
Inside this procedure I want to calculate an array phiN(1),phiN(2),...phiN(18) out of the variables a-e which itself is a list, e.g.
set phiN(1) [list 1 2 3 4 5 6 7 8 9];
(lets say the values 1-9 had been calculated out of the input variables a-e). And I want to calculate some other parameter alpha and beta
set alpha [expr a+b];
set beta [expr c+d];
Anyway no I want to pass these new calculated variables outside of my procedure. Compare to matlab I simply would write sg like to get these variables outside of the 'function'.
[phiN,alpha,beta] = myproc{a b c d e}
Has anybody an idea how I can deal in tcl?? Thanks!

Answer 1

There are several options:
Return a list and use lassign outside
Example:
proc myproc {a b c d e} {
set alpha [expr {$a+$b}]
set beta [expr {$c+$d}]
return [list $alpha $beta]
}
lassign [myproc 1 2 3 4 5] alpha beta
This is fine if you return values, but not arrays.
Use upvar and provide the name of the array/variable as argument
Example:
proc myproc {phiNVar a b c d e} {
upvar 1 $phiNVar phiN
# Now use phiN as local variable
set phiN(1) [list 1 2 3 4 5 6 7 8 9]
}
# Usage
myproc foo 1 2 3 4 5
foreach i $foo(1) {
puts $i
}
Use a combination of both
Example:
proc myproc {phiNVar a b c d e} {
uplevel 1 $phiNVar phiN
set alpha [expr {$a+$b}]
set beta [expr {$c+$d}]
set phiN(1) [list 1 2 3 4 5 6 7 8 9]
return [list $alpha $beta]
}
lassign [myproc bar 1 2 3 4 5] alpha beta
foreach i $bar(1) {
puts $i
}
Edit: As Donal suggested, is is also possible to return a dict:
A dict is a Tcl list where the odd elements are the keys and the even elements are the values. You can convert an array to a dict with array get and convert a dict back to an array with array set. You can also use the dict itself.
Example
proc myproc {a b c d e} {
set alpha [expr {$a+$b}]
set beta [expr {$c+$d}]
set phiN(1) [list 1 2 3 4 5 6 7 8 9]
return [list [array get phiN] $alpha $beta]
}
lassign [myproc 1 2 3 4 5] phiNDict alpha beta
array set bar $phiNDict
foreach i $bar(1) {
puts $i
}
# Use the [dict] command to manipulate the dict directly
puts [dict get $phiNDict 1]
For more ideas (this is about arrays, but could apply to values as well) see this wiki entry.