From page 319, 'makecoroutine'

define resume = 0

- 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

===========================================================================

from page 316, coroutine example

- 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

===========================================================================
page 313, breakpoints

--> define toplevel = 0
--> letcont cont in toplevel := cont
--> define resume = 0
--> define break = proc (x) letcont cont in begin resume := cont; error(); toplevel (x) end
--> +(break(1),break(2))
--> resume(100
--> +(break(1), break(2))

===========================================================================

guaranteed to bring your machine down.
define tak = 0
tak := proc (x,y,z) if lesser(y,x) then tak(tak(sub1(x),y,z),tak(sub1(y),z,x),tak(sub1(z),x,y)) else z