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recursive tag unions

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This commit is contained in:
Folkert 2020-08-31 14:29:09 +02:00
parent ba186bfe09
commit f9cf4ea371
8 changed files with 286 additions and 75 deletions
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106
compiler/unify/src/unify.rs
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@ -565,43 +565,84 @@ fn unify_shared_tags(
// and so on until the whole non-recursive tag union can be unified with it.
let mut problems = Vec::new();
let attr_wrapped = match (subs.get(expected).content, subs.get(actual).content) {
(
Content::Structure(FlatType::Apply(Symbol::ATTR_ATTR, expected_args)),
Content::Structure(FlatType::Apply(Symbol::ATTR_ATTR, actual_args)),
) => Some((
expected_args[0],
expected_args[1],
actual_args[0],
actual_args[1],
)),
_ => None,
};
if let Some(rvar) = recursion_var {
if expected == rvar {
problems.extend(unify_pool(subs, pool, actual, ctx.second));
println!("A");
} else if is_structure(actual, subs) {
// the recursion variable is hidden behind some structure (commonly an Attr
// with uniqueness inference). Thus we must expand the recursive tag union to
// unify if with the non-recursive one. Thus:
match attr_wrapped {
None => {
if expected == rvar {
if actual == rvar {
problems.extend(unify_pool(subs, pool, expected, actual));
} else {
problems.extend(unify_pool(subs, pool, actual, ctx.second));
// replace the rvar with ctx.second (the whole recursive tag union) in expected
subs.explicit_substitute(rvar, ctx.second, expected);
// this unification is required for layout generation,
// but causes worse error messages
problems.extend(unify_pool(subs, pool, expected, actual));
}
} else if is_structure(actual, subs) {
// the recursion variable is hidden behind some structure (commonly an Attr
// with uniqueness inference). Thus we must expand the recursive tag union to
// unify if with the non-recursive one. Thus:
// but, by the `is_structure` condition above, only if we're unifying with a structure!
// when `actual` is just a flex/rigid variable, the substitution would expand a
// recursive tag union infinitely!
// replace the rvar with ctx.second (the whole recursive tag union) in expected
subs.explicit_substitute(rvar, ctx.second, expected);
problems.extend(unify_pool(subs, pool, actual, expected));
println!("B");
} else {
// unification with a non-structure is trivial
problems.extend(unify_pool(subs, pool, actual, expected));
println!("C");
// but, by the `is_structure` condition above, only if we're unifying with a structure!
// when `actual` is just a flex/rigid variable, the substitution would expand a
// recursive tag union infinitely!
problems.extend(unify_pool(subs, pool, actual, expected));
} else {
// unification with a non-structure is trivial
problems.extend(unify_pool(subs, pool, actual, expected));
}
}
Some((_expected_uvar, inner_expected, _actual_uvar, inner_actual)) => {
if inner_expected == rvar {
if inner_actual == rvar {
problems.extend(unify_pool(subs, pool, actual, expected));
} else {
problems.extend(unify_pool(subs, pool, inner_actual, ctx.second));
problems.extend(unify_pool(subs, pool, expected, actual));
}
} else if is_structure(inner_actual, subs) {
// the recursion variable is hidden behind some structure (commonly an Attr
// with uniqueness inference). Thus we must expand the recursive tag union to
// unify if with the non-recursive one. Thus:
// replace the rvar with ctx.second (the whole recursive tag union) in expected
subs.explicit_substitute(rvar, ctx.second, inner_expected);
// but, by the `is_structure` condition above, only if we're unifying with a structure!
// when `actual` is just a flex/rigid variable, the substitution would expand a
// recursive tag union infinitely!
problems.extend(unify_pool(subs, pool, actual, expected));
} else {
// unification with a non-structure is trivial
problems.extend(unify_pool(subs, pool, actual, expected));
}
}
}
} else {
// we always unify NonRecursive with Recursive, so this should never happen
debug_assert_ne!(Some(actual), recursion_var);
problems.extend(unify_pool(subs, pool, actual, expected));
println!("D");
};
// TODO this changes some error messages
// but is important for the inference of recursive types
if problems.is_empty() {
problems.extend(unify_pool(subs, pool, expected, actual));
}
if problems.is_empty() {
// debug_assert_eq!(subs.get_root_key(actual), subs.get_root_key(expected));
matching_vars.push(actual);
@ -695,8 +736,19 @@ fn unify_flat_type(
unify_tag_union(subs, pool, ctx, union1, union2, (None, None))
}
(RecursiveTagUnion(_, _, _), TagUnion(_, _)) => {
unreachable!("unify of recursive with non-recursive tag union should not occur");
(RecursiveTagUnion(recursion_var, tags1, ext1), TagUnion(tags2, ext2)) => {
// unreachable!("unify of recursive with non-recursive tag union should not occur");
let union1 = gather_tags(subs, tags1.clone(), *ext1);
let union2 = gather_tags(subs, tags2.clone(), *ext2);
unify_tag_union(
subs,
pool,
ctx,
union1,
union2,
(None, Some(*recursion_var)),
)
}
(TagUnion(tags1, ext1), RecursiveTagUnion(recursion_var, tags2, ext2)) => {