NAME
AddPrologue — Add code to the beginning of a proc.
SYNOPSIS
AddPrologue ProcName Prologue
DESCRIPTION
Return Value
None
Arguments
ProcNameName of proc to add prologue to.
PrologueCode to add to the start of the proc body.
More Info
Note that one could alternatively use the trace command.

For information regarding exceptions / errors, see here.
EXAMPLES 
% proc Tester {one two} {puts "$one $two"}
% Tester a b
a b
% AddPrologue Tester {puts "123"}
% Tester c d
123
c d
SEE ALSO
AddEpilogue, trace
KEYWORDS
append, command, concatenate, procedure