rushing:~/python/eopl/9.4$ python interp.py
--> - define test = proc (x)
...     while greater(x,0) do
...       begin
...         print (x);
...         x := sub1(x)
...       end
... 

expanded to:
['definition',
 'test',
 ['proc',
  ['x'],
  ['app',
   ['proc',
    ['_g0'],
    ['app',
     ['proc', ['ignore', 'thunk'], ['app', ['varref', 'thunk'], []]],
     [['app',
       ['proc', ['_g1'], ['varassign', '_g0', ['varref', '_g1']]],
       [['proc',
         [],
         ['conditional',
          ['app',
           ['varref', 'greater'],
           [['varref', 'x'], ['lit', 0]]],
          ['app',
           ['proc',
            ['ignore', 'thunk'],
            ['app', ['varref', 'thunk'], []]],
           [['app',
             ['proc',
              ['ignore', 'thunk'],
              ['app', ['varref', 'thunk'], []]],
             [['app', ['varref', 'print'], [['varref', 'x']]],
              ['proc',
               [],
               ['varassign',
                'x',
                ['app', ['varref', 'sub1'], [['varref', 'x']]]]]]],
            ['proc', [], ['app', ['varref', '_g0'], []]]]],
          ['lit', 0]]]]],
      ['proc', [], ['app', ['varref', '_g0'], []]]]]],
   [['lit', 0]]]]]
=>
<undefined>
[0 environments]
--> test(10)
expanded to:
['app', ['varref', 'test'], [['lit', 10]]]
=>
[10]
[9]
[8]
[7]
[6]
[5]
[4]
[3]
[2]
[1]
0
[56 environments]
--> 




--> define resume = 0
=>
<undefined>
[0 environments]
--> - define makecoroutine =
  proc (body)
    let lcs = 0
    in letrecproc
      newcoroutine (value) = lcs(value);
      localresume (cont, value) =
        let receivedvalue = letcont localcont
                              in begin
                                lcs := localcont;
                                cont (value)
                              end
          in begin
              resume := localresume;
              receivedvalue
            end
      in letcont exit
        in begin
          body(localresume (exit, newcoroutine));
          error()
        end

=>
<undefined>
[0 environments]
--> 
- define example =
  proc ()
    letcont returncont
    in let co1 = 0;
           co2 = 0
       in begin
          co1 := makecoroutine (
              proc (initval1) 
                begin
                  print(1);
                  print(initval1);
                  initval1 := resume (co2, add1 (initval1));
                  print (1);
                  print (initval1);
                  initval1 := resume (co2, add1 (initval1));
                  returncont (initval1)
                end
          );
          co2 := makecoroutine (
              proc (initval2)
                begin
                  print (2);
                  print (initval2);
                  initval2 := resume (co1, add1 (initval2));
                  print (2);
                  print (initval2);
                  resume (co1, add1 (initval2))
                end
          );
          co1(33)
      end

=>
<undefined>
[0 environments]
--> 
--> example()
expanded to:
['app', ['varref', 'example'], []]
=>
[1]
[33]
[2]
[34]
[1]
[35]
[2]
[36]
37
[93 environments]
-->