Question

i am having a following code:

proc testList {setupFile ""} {
  if {$setupFile == ""} {
    set setupFile location
  }
}
proc run {} {
  puts "$setupFile"
}

I am getting syntax error. I know if i declare the setupFile variable outside the proc i.e in the main proc then i can append it with namespace say ::65WL::setupFile to make it global but not getting how to do that if a variable itself is defined in the proc only.

Answer 1

Tcl variables that are not local to a specific procedure run need to be bound to a namespace; the namespace can be the global namespace (there’s a special command for that) but doesn’t need to be. Thus, to have a variable that is shared between two procedures, you need to give it an exposed name:

proc testList {{setup_file ""}} {
  # Use the 'eq' operator; more efficient for string equality
  if {$setup_file eq ""} {
    set setup_file location
  }
  global setupFile
  set setupFile $setup_file
}
proc run {} {
  global setupFile
  puts "$setupFile"
}

Now, that’s for sharing a full variable. There are some other alternatives provided you only want to share a value. For example, these two possibilities:

proc testList {{setup_file ""}} {
  if {$setup_file eq ""} {
    set setup_file location
  }
  # Create a procedure body at run-time
  proc run {} [concat [list set setupFile $setup_file] \; {
    puts "$setupFile"
  }]
}

proc testList {{setup_file ""}} {
  if {$setup_file eq ""} {
    set setup_file location
  }
  # Set the value through combined use of aliases and a lambda term
  interp alias {} run {} apply {setupFile {
    puts "$setupFile"
  }} $setup_file
}

There are more options with Tcl 8.6, but that’s still in beta.