path: root/cpp/044space_surround

//: So far you can have global variables by not setting default-space, and
//: local variables by setting default-space. You can isolate variables
//: between those extremes by creating 'surrounding' spaces.
//:
//: (Surrounding spaces are like lexical scopes in other languages.)

:(scenario "surrounding_space")
# location 1 in space 1 refers to the space surrounding the default space, here 20.
recipe main [
  10:integer <- copy 5:literal  # pretend array
  20:integer <- copy 5:literal  # pretend array
  default-space:address:array:location <- copy 10:literal
  0:address:array:location/names:dummy <- copy 20:literal  # later layers will explain the /names: property
  1:integer <- copy 32:literal
  1:integer/space:1 <- copy 33:literal
]
+run: instruction main/3
+mem: storing 20 in location 11
+run: instruction main/4
+mem: storing 32 in location 12
+run: instruction main/5
+mem: storing 33 in location 22

//: If you think of a space as a collection of variables with a common
//: lifetime, surrounding allows managing shorter lifetimes inside a longer
//: one.

:(replace{} "int space_base(const reagent& x)")
int space_base(const reagent& x) {
  return space_base(x, space_index(x), Current_routine->calls.top().default_space);
}

int space_base(const reagent& x, int space_index, int base) {
//?   trace("foo") << "base of space " << space_index << '\n'; //? 1
  if (space_index == 0) {
//?     trace("foo") << "base of space " << space_index << " is " << base << '\n'; //? 1
    return base;
  }
//?   trace("foo") << "base of space " << space_index << " is " << Memory[base+1] << '\n'; //? 1
  int result = space_base(x, space_index-1, Memory[base+1]);
  return result;
}

int space_index(const reagent& x) {
  for (size_t i = 0; i < x.properties.size(); ++i) {
    if (x.properties[i].first == "space")
      return to_int(x.properties[i].second[0]);
  }
  return 0;
}