static ast_result_t flatten_isect(pass_opt_t* opt, ast_t* ast)
{
// Flatten intersections without testing subtyping. This is to preserve any
// type guarantees that an element in the intersection might make.
// If there are more than 2 children, this has already been flattened.
if(ast_childcount(ast) > 2)
return AST_OK;
AST_EXTRACT_CHILDREN(ast, left, right);
if((opt->check.frame->constraint == NULL) &&
(opt->check.frame->iftype_constraint == NULL) &&
(opt->check.frame->provides == NULL) &&
!is_compat_type(left, right))
{
ast_add(ast, right);
ast_add(ast, left);
ast_error(opt->check.errors, ast,
"intersection types cannot include reference capabilities that are not "
"locally compatible");
return AST_ERROR;
}
flatten_typeexpr_element(ast, left, TK_ISECTTYPE);
flatten_typeexpr_element(ast, right, TK_ISECTTYPE);
return AST_OK;
}
static bool is_arrow_compat_arrow(ast_t* a, ast_t* b)
{
// S = this | A {#read, #send, #share, #any}
// K = N k | A {iso, trn, ref, val, box, tag} | K->K | (empty)
// L = S | K
// T = N k | A k | L->T
//
// forall K' in S . K->S->T1 {S |-> K'} ~ T2 {S |-> K'}
// ---
// K->S->T1 ~ T2
ast_t* r_a;
ast_t* r_b;
if(viewpoint_reifypair(a, b, &r_a, &r_b))
{
bool ok = is_compat_type(r_a, r_b);
ast_free_unattached(r_a);
ast_free_unattached(r_b);
return ok;
}
// No elements need reification.
//
// lowerbound(T1->T2) ~ lowerbound(T3->T4)
// ---
// T1->T2 ~ T3->T4
r_a = viewpoint_lower(a);
if(r_a == NULL)
return false;
r_b = viewpoint_lower(b);
if(r_b == NULL)
{
ast_free_unattached(r_a);
return false;
}
bool ok = is_compat_type(r_a, r_b);
ast_free_unattached(r_a);
ast_free_unattached(r_b);
return ok;
}
static bool is_arrow_compat_nominal(ast_t* a, ast_t* b)
{
// lowerbound(T1->T2) ~ N k
// ---
// T1->T2 ~ N k
ast_t* a_lower = viewpoint_lower(a);
if(a == NULL)
return false;
bool ok = is_compat_type(a_lower, b);
ast_free_unattached(a_lower);
return ok;
}
static bool is_union_compat_x(ast_t* a, ast_t* b)
{
// T1 ~ T3 or T2 ~ T3
// ---
// (T1 | T2) ~ T3
for(ast_t* child = ast_child(a);
child != NULL;
child = ast_sibling(child))
{
if(is_compat_type(child, b))
return true;
}
return false;
}
static bool is_tuple_compat_tuple(ast_t* a, ast_t* b)
{
// T1 ~ T3
// T2 ~ T4
// ---
// (T1, T2) ~ (T3, T4)
ast_t* a_child = ast_child(a);
ast_t* b_child = ast_child(b);
while((a_child != NULL) && (b_child != NULL))
{
if(!is_compat_type(a_child, b_child))
return false;
a_child = ast_sibling(a_child);
b_child = ast_sibling(b_child);
}
return (a_child == NULL) && (b_child == NULL);
}
static bool is_arrow_compat_typeparam(ast_t* a, ast_t* b)
{
// forall k' in k . T1->T2 {A k |-> A k'} ~ A k'
// ---
// T1->T2 ~ A k
ast_t* r_a = viewpoint_reifytypeparam(a, b);
ast_t* r_b = viewpoint_reifytypeparam(b, b);
if(r_a != NULL)
{
bool ok = is_compat_type(r_a, r_b);
ast_free_unattached(r_a);
ast_free_unattached(r_b);
return ok;
}
// lowerbound(T1->T2) ~ A k
// ---
// T1->T2 ~ A k
return is_arrow_compat_nominal(a, b);
}
