archive/1.vm/044space_surround.cc

   1 //: So far you can have global variables by not setting default-space, and
   2 //: local variables by setting default-space. You can isolate variables
   3 //: between those extremes by creating 'surrounding' spaces.
   4 //:
   5 //: (Surrounding spaces are like lexical scopes in other languages.)
   6
   7 void test_surrounding_space() {
   8   run(
   9       // location 2 in space 1 (remember that locations 0 and 1 are reserved in all
  10       // spaces) refers to the space surrounding the default space, here 20.
  11       "def main [\n"
  12          // prepare default-space address
  13       "  10:num/alloc-id, 11:num <- copy 0, 1000\n"
  14          // prepare default-space payload
  15       "  1000:num <- copy 0\n"  // alloc id of payload
  16       "  1001:num <- copy 5\n"  // length
  17          // prepare address of chained space
  18       "  20:num/alloc-id, 21:num <- copy 0, 2000\n"
  19          // prepare payload of chained space
  20       "  2000:num <- copy 0\n"  // alloc id of payload
  21       "  2001:num <- copy 5\n"  // length
  22          // actual start of this recipe
  23       "  default-space:space <- copy 10:space\n"
  24          // later layers will explain the /names: property
  25       "  0:space/names:dummy <- copy 20:space/raw\n"
  26       "  2:num <- copy 94\n"
  27       "  2:num/space:1 <- copy 95\n"
  28       "]\n"
  29       "def dummy [\n"  // just for the /names: property above
  30       "]\n"
  31   );
  32   CHECK_TRACE_CONTENTS(
  33       // chain space: 1000 + (alloc id) 1 + (length) 1
  34       "mem: storing 0 in location 1002\n"
  35       "mem: storing 2000 in location 1003\n"
  36       // store to default space: 1000 + (alloc id) 1 + (length) 1 + (index) 2
  37       "mem: storing 94 in location 1004\n"
  38       // store to chained space: (contents of location 1003) 2000 + (alloc id) 1 + (length) 1 + (index) 2
  39       "mem: storing 95 in location 2004\n"
  40   );
  41 }
  42
  43 //: If you think of a space as a collection of variables with a common
  44 //: lifetime, surrounding allows managing shorter lifetimes inside a longer
  45 //: one.
  46
  47 :(replace{} "int space_base(const reagent& x)")
  48 int space_base(const reagent& x) {
  49   int base = current_call().default_space ? (current_call().default_space+/*skip alloc id*/1) : 0;
  50   return space_base(x, space_index(x), base);
  51 }
  52
  53 int space_base(const reagent& x, int space_index, int base) {
  54   if (space_index == 0)
  55     return base;
  56   double chained_space_address = base+/*skip length*/1+/*skip alloc id of chaining slot*/1;
  57   double chained_space_base = get_or_insert(Memory, chained_space_address) + /*skip alloc id of chained space*/1;
  58   return space_base(x, space_index-1, chained_space_base);
  59 }
  60
  61 int space_index(const reagent& x) {
  62   for (int i = 0;  i < SIZE(x.properties);  ++i) {
  63     if (x.properties.at(i).first == "space") {
  64       if (!x.properties.at(i).second || x.properties.at(i).second->right)
  65         raise << maybe(current_recipe_name()) << "/space metadata should take exactly one value in '" << x.original_string << "'\n" << end();
  66       return to_integer(x.properties.at(i).second->value);
  67     }
  68   }
  69   return 0;
  70 }
  71
  72 :(code)
  73 void test_permit_space_as_variable_name() {
  74   run(
  75       "def main [\n"
  76       "  space:num <- copy 0\n"
  77       "]\n"
  78   );
  79 }