A simple step-by-step debugger for Guu language

Guu program is a collection of procedures. Every procedure begins with the sub keyword and the name of the procedure and ends with other procedure declaration (or with file end if the procedure is final). Execution starts from the main procedure

A procedure body is an instructions sequence. At the start of a line can be any count of spaces and tabs. Empty lines should be ignored. Guu doesn't have a comments block.

Guu has only three statements: - set (varname) (new value) - set a new value to variable. - call (subname) - call a procedure (calls can be recursive). - print (varname) - print a value of variable.

Variables in Guu language exist only in the global scope. So, the next program will print 2:

sub main
  set a 1
  call foo
  print a

sub foo
  set a 2