Tcl procedures and scopes

proc introduces a new procedure.
% proc foo {a b} {
puts "a = $a, b = $b"
}
% foo alpha beta
a = alpha, b = beta

Variables used in a procedure have local scope unless explicitly declared global:
% set v 100
100
% proc p {} {
puts $v
}
% p
can't read "v": no such variable
% proc p {} {
global v
puts $v
}
% p
100

More insane scoping facilities are provided with upvar and uplevel. Avoid them if at all possible.

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