Hello,

are there any documentation how to implement call/cc call on top of GVM?

So far, looking at the use of the register 0 and jumps at the end of basic blocks, I optimistic concluded that GVM code is in the continuation-passing style. (Is it true?) Therefore, I tried a call/cc definition from "The 90 minute Scheme to C compiler":

(define call/cc (lambda (k f) (f k (lambda (dummy-k result) (k result)))))

A pseudocode for a GVM interpreter looks like:

#<primitive ##call-with-current-continuation>: pc = reg1 reg1 = new continuation(reg0) goto pc

A jump to the continuation is: pc = continuation.get_label() goto pc

It nearly worked, but I don't know what to do with the stack. Consider an example:

(define (f return) (return 2) 3) (display (f (lambda (x) x)))(newline) ; displays 3 (display (call-with-current-continuation f))(newline) ; displays 2

Here is the GVM code for the #<procedure ~#f>:

#1 0 entry-point 1 () -1 = +0 -2 = +1 +1 = '2 +0 = #3 -3 = . -4 = . jump* 4 #2

A new stack frame is allocated.

#2 4 jump 4 -2 1

Exit from ~#f due to the jump to the continuation. But: the stack frame still exists, it is not revoked. Therefore in

jump 4 '#<primitive ##call-with-current-continuation> 1 #6 4 return-point +0 = #7 jump 4 '#<primitive display> 1 #7 4 return-point +0 = -1 jump* 4 #8

the register 0 is restored using the wrong frame.

How to restore the stack correctly when jumping to a continuation?