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//: Exclusive containers contain exactly one of a fixed number of 'variants'
//: of different types.
//:
//: They also implicitly contain a tag describing precisely which variant is
//: currently stored in them.
:(before "End Mu Types Initialization")
//: We'll use this container as a running example, with two number elements.
{
type_ordinal tmp = Type_ordinal["number-or-point"] = Next_type_ordinal++;
Type[tmp].size = 2;
Type[tmp].kind = exclusive_container;
Type[tmp].name = "number-or-point";
vector<type_ordinal> t1;
t1.push_back(number);
Type[tmp].elements.push_back(t1);
vector<type_ordinal> t2;
t2.push_back(point);
Type[tmp].elements.push_back(t2);
Type[tmp].element_names.push_back("i");
Type[tmp].element_names.push_back("p");
}
//: Tests in this layer often explicitly setup memory before reading it as an
//: array. Don't do this in general. I'm tagging exceptions with /raw to
//: avoid warnings.
:(scenario copy_exclusive_container)
# Copying exclusive containers copies all their contents and an extra location for the tag.
recipe main [
1:number <- copy 1 # 'point' variant
2:number <- copy 34
3:number <- copy 35
4:number-or-point <- copy 1:number-or-point/raw # unsafe
]
+mem: storing 1 in location 4
+mem: storing 34 in location 5
+mem: storing 35 in location 6
:(before "End size_of(types) Cases")
if (t.kind == exclusive_container) {
// size of an exclusive container is the size of its largest variant
// (So like containers, it can't contain arrays.)
long long int result = 0;
for (long long int i = 0; i < t.size; ++i) {
long long int tmp = size_of(t.elements.at(i));
if (tmp > result) result = tmp;
}
// ...+1 for its tag.
return result+1;
}
//:: To access variants of an exclusive container, use 'maybe-convert'.
//: It always returns an address (so that you can modify it) or null (to
//: signal that the conversion failed (because the container contains a
//: different variant).
//: 'maybe-convert' requires a literal in ingredient 1. We'll use a synonym
//: called 'variant'.
:(before "End Mu Types Initialization")
Type_ordinal["variant"] = 0;
:(scenario maybe_convert)
recipe main [
12:number <- copy 1
13:number <- copy 35
14:number <- copy 36
20:address:point <- maybe-convert 12:number-or-point/raw, 1:variant # unsafe
]
+mem: storing 13 in location 20
:(scenario maybe_convert_fail)
recipe main [
12:number <- copy 1
13:number <- copy 35
14:number <- copy 36
20:address:point <- maybe-convert 12:number-or-point/raw, 0:variant # unsafe
]
+mem: storing 0 in location 20
:(before "End Primitive Recipe Declarations")
MAYBE_CONVERT,
:(before "End Primitive Recipe Numbers")
Recipe_ordinal["maybe-convert"] = MAYBE_CONVERT;
:(before "End Primitive Recipe Implementations")
case MAYBE_CONVERT: {
if (SIZE(ingredients) != 2) {
raise << current_recipe_name() << ": 'maybe-convert' expects exactly 2 ingredients in '" << current_instruction().to_string() << "'\n" << end();
break;
}
reagent base = canonize(current_instruction().ingredients.at(0));
long long int base_address = base.value;
if (base_address == 0) {
raise << current_recipe_name() << ": tried to access location 0 in '" << current_instruction().to_string() << "'\n" << end();
break;
}
type_ordinal base_type = base.types.at(0);
if (Type[base_type].kind != exclusive_container) {
raise << current_recipe_name () << ": first ingredient of 'maybe-convert' should be an exclusive-container, but got " << base.original_string << '\n' << end();
break;
}
if (!is_literal(current_instruction().ingredients.at(1))) {
raise << current_recipe_name() << ": second ingredient of 'maybe-convert' should have type 'variant', but got " << current_instruction().ingredients.at(1).original_string << '\n' << end();
break;
}
long long int tag = current_instruction().ingredients.at(1).value;
long long int result;
if (tag == static_cast<long long int>(Memory[base_address])) {
result = base_address+1;
}
else {
result = 0;
}
products.resize(1);
products.at(0).push_back(result);
break;
}
//:: Allow exclusive containers to be defined in mu code.
:(scenario exclusive_container)
exclusive-container foo [
x:number
y:number
]
+parse: reading exclusive-container foo
+parse: element name: x
+parse: type: 1
+parse: element name: y
+parse: type: 1
:(before "End Command Handlers")
else if (command == "exclusive-container") {
insert_container(command, exclusive_container, in);
}
//:: To construct exclusive containers out of variant types, use 'merge'.
:(scenario lift_to_exclusive_container)
exclusive-container foo [
x:number
y:number
]
recipe main [
1:number <- copy 34
2:foo <- merge 0/x, 1:number
4:foo <- merge 1/x, 1:number
]
+mem: storing 0 in location 2
+mem: storing 34 in location 3
+mem: storing 1 in location 4
+mem: storing 34 in location 5
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