With inlined byte code disassembly (and some braces and newlines):
>int main()
>{
=== 3 1c entry
=== 3 30 function start
=== 3 30 mark_at(0)
=== 3 54 pop to mark
=== 3 90 fill_stack(4,0)
=== 3 b6 init_frame(0,4)
> array(int) positions=({4,3});
=== 4 be constant(0)
=== 4 e5 copy_value
=== 4 ed assign local and pop(0)
> int pos=1;
=== 5 123 assign local number and pop(1,1)
> array unrolled=({});
=== 6 160 mark, call builtin(1)
=== 6 176 assign local and pop(2)
=== 7 1b3 local(0)
=== 7 1e0 & local(3)
=== 7 203 clear local(3)
=== 7 236 push 0
=== 7 24d branch(3)
> foreach (positions, int nextpos)
> {
=== 7 252 label(5)
> write("Extending to %d\n",nextpos);
=== 9 261 string(1)
=== 9 28b local(3)
=== 9 2b1 apply N(2,2)
=== 9 2c5 pop
=== 10 2f1 --local(1)
=== 10 34b ~
=== 10 362 local(3)
=== 10 388 add integer(1)
=== 10 3d1 int+int
=== 10 403 branch(6)
> for (;pos<=nextpos;++pos) {
=== 10 408 label(7)
> unrolled += ({"Spam"});
=== 10 417 mark
=== 10 42b & local(2)
=== 10 44e push 0
=== 10 465 string(2)
=== 10 481 append array
=== 10 489 pop
=== 10 4b1 label(6)
=== 10 4c0 loop(7)
> }
=== 10 521 local(3)
=== 10 547 add integer(1)
=== 10 590 assign local and pop(1)
=== 7 5ca label(3)
=== 7 5d9 foreach(5)
> }
=== 7 67f pop_n_elems(4)
=== 12 68d clear n local(0,4)
=== 12 6d4 return 0
>}
Looks like the problem is either in the loop opcode, or in the setup.
