MAD: printing variables in stack frames other than the current one gives incorrect results

[lutzhamel]

Printing variables in stack frames other than the current one gives incorrect results. Consider the program,

load system io.

function fact
   with 0 do
      1
   with n do
      n*fact(n-1)
end

io @println (fact 3)

when using MAD ,

lutz$ asteroid -d fact.ast
Minimal Asteroid Debugger 0.0.1
(c) University of Rhode Island
type "help" for additional information
mad> next
>  1 load system io.
   2 
   3 function fact
   4    with 0 do
   5       1
mad> next
   1 load system io.
   2 
>  3 function fact
   4    with 0 do
   5       1
   6    with n do
   7       n*fact(n-1)
mad> set 7
mad> cont
reached breakpoint (fact.ast:7)
   4    with 0 do
   5       1
   6    with n do
>  7       n*fact(n-1)
   8 end
   9 
   10 io @println (fact 3)
   11 
mad> cont
reached breakpoint (fact.ast:7)
   4    with 0 do
   5       1
   6    with n do
>  7       n*fact(n-1)
   8 end
   9 
   10 io @println (fact 3)
   11 
mad> stack
Runtime stack (most recent call first):
frame #0: fact.ast @fact
frame #1: fact.ast @fact
frame #2: fact.ast @<toplevel>
mad> print n
n: 2
mad> up
you are looking at frame #1
mad> print n
n: 2                        <<<< this should be 3
mad> 

Notice that we keep returning the value of n associated with the current frame.

[NicholasRM]

This seems like something that happens with how the debugger handles print * and print $SYM. Calling print * tells the debugger to load the current stack frame from the SymTab with MAD's self.frame_ix. However, print $SYM is handled by calling the SymTab method .lookup_sym(), which then calls .find_sym_dict() to return the first dictionary that contains a specific symbol. This is why calling print * correctly displays the value of n in different scopes.

Minimal Asteroid Debugger 0.0.1
(c) University of Rhode Island
type "help" for additional information
mad> next
>  1 load system io.
   2
   3 function fact
   4    with 0 do
   5       1
mad> next
   1 load system io.
   2
>  3 function fact
   4    with 0 do
   5       1
   6    with n do
   7       n*fact(n-1)
mad> set 7
mad> cont
reached breakpoint (.\fact.ast:7)
   4    with 0 do
   5       1
   6    with n do
>  7       n*fact(n-1)
   8 end
   9
   10 io @println (fact 3
   11 [EOF]
mad> cont
reached breakpoint (.\fact.ast:7)
   4    with 0 do
   5       1
   6    with n do
>  7       n*fact(n-1)
   8 end
   9
   10 io @println (fact 3
   11 [EOF]
mad> stack
Runtime stack (most recent call first):
frame #0: .\fact.ast @fact
frame #1: .\fact.ast @fact
frame #2: .\fact.ast @<toplevel>
mad> print n
n: 2
mad> up
you are looking at frame #1
mad> print n
n: 2
mad> print *
n: 3
mad> down
you are looking at frame #0
mad> print *
n: 2
mad>

This else branch in ._handle_print()may need to get the current scope instead of looking up the symbol from the table directly.

# mad.py
def _handle_print(self,args):
      # ...
      if args[0] == '*':
         var_list = self.interp_state.symbol_table.get_curr_scope(scope=self.frame_ix, option="items")
         for (name,val) in var_list:
            print("{}: {}".format(name,term2string(val)))
      else:
         val = self.interp_state.symbol_table.lookup_sym(args[0],strict=False)
         if not val:
            print("error: variable {} not found".format(args[0]))
         else:
            print("{}: {}".format(args[0],term2string(val)))
      return START_DEBUGGER