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//: 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.
def main [
# pretend shared:array:location; in practice we'll use new
10:number <- copy 0 # refcount
11:number <- copy 5 # length
# pretend shared:array:location; in practice we'll use new
20:number <- copy 0 # refcount
21:number <- copy 5 # length
# actual start of this recipe
default-space:address:shared:array:location <- copy 10/unsafe
0:address:shared:array:location/names:dummy <- copy 20/unsafe # later layers will explain the /names: property
1:number <- copy 32
1:number/space:1 <- copy 33
]
def dummy [ # just for the /names: property above
]
# chain space: 10 + /*skip refcount*/1 + /*skip length*/1
+mem: storing 20 in location 12
# store to default space: 10 + /*skip refcount*/1 + /*skip length*/1 + /*index*/1
+mem: storing 32 in location 13
# store to chained space: /*contents of location 12*/20 + /*skip refcount*/1 + /*skip length*/1 + /*index*/1
+mem: storing 33 in location 23
//: 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) {
int base = current_call().default_space ? (current_call().default_space+/*skip refcount*/1) : 0;
return space_base(x, space_index(x), base);
}
int space_base(const reagent& x, int space_index, int base) {
if (space_index == 0)
return base;
int result = space_base(x, space_index-1, get_or_insert(Memory, base+/*skip length*/1))+/*skip refcount*/1;
return result;
}
int space_index(const reagent& x) {
for (int i = 0; i < SIZE(x.properties); ++i) {
if (x.properties.at(i).first == "space") {
if (!x.properties.at(i).second || x.properties.at(i).second->right)
raise << maybe(current_recipe_name()) << "/space metadata should take exactly one value in " << x.original_string << '\n' << end();
return to_integer(x.properties.at(i).second->value);
}
}
return 0;
}
:(scenario permit_space_as_variable_name)
def main [
space:number <- copy 0
]
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