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fix(library/unifier): try to generate approximate solution for flex-flex constraints before discarding them

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fixes #662
This commit is contained in:
Leonardo de Moura 2015-06-09 14:18:24 -07:00
parent d287b20018
commit e3a0e62859
4 changed files with 136 additions and 45 deletions
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110
src/library/unifier.cpp
View file

@ -1401,6 +1401,31 @@ struct unifier_fn {
cs = append(aux, cs);
}
/** \see ensure_sufficient_args */
expr ensure_sufficient_args_core(expr mtype, unsigned nargs, unsigned i, constraint_seq & cs) {
if (i == nargs)
return mtype;
mtype = m_tc->ensure_pi(mtype, cs);
expr local = mk_local_for(mtype);
expr body = instantiate(binding_body(mtype), local);
return Pi(local, ensure_sufficient_args_core(body, nargs, i+1, cs));
}
/** \brief Make sure mtype is a Pi of size at least nargs.
If it is not, we use ensure_pi and (potentially) add new constaints to enforce it.
*/
expr ensure_sufficient_args(expr const & mtype, unsigned nargs, constraint_seq & cs) {
expr t = mtype;
unsigned num = 0;
while (is_pi(t)) {
num++;
t = binding_body(t);
}
if (num >= nargs)
return mtype;
return ensure_sufficient_args_core(mtype, nargs, 0, cs);
}
/** \brief Auxiliary functional object for implementing process_flex_rigid_core */
class flex_rigid_core_fn {
unifier_fn & u;
@ -1470,29 +1495,9 @@ struct unifier_fn {
return true;
}
/** \see ensure_sufficient_args */
expr ensure_sufficient_args_core(expr mtype, unsigned i, constraint_seq & cs) {
if (i == margs.size())
return mtype;
mtype = tc().ensure_pi(mtype, cs);
expr local = u.mk_local_for(mtype);
expr body = instantiate(binding_body(mtype), local);
return Pi(local, ensure_sufficient_args_core(body, i+1, cs));
}
/** \brief Make sure mtype is a Pi of size at least margs.size().
If it is not, we use ensure_pi and (potentially) add new constaints to enforce it.
*/
/** \brief Make sure mtype is a Pi of size at least margs.size(). */
expr ensure_sufficient_args(expr const & mtype, constraint_seq & cs) {
expr t = mtype;
unsigned num = 0;
while (is_pi(t)) {
num++;
t = binding_body(t);
}
if (num >= margs.size())
return mtype;
return ensure_sufficient_args_core(mtype, 0, cs);
return u.ensure_sufficient_args(mtype, margs.size(), cs);
}
/**
@ -1970,6 +1975,63 @@ struct unifier_fn {
postpone(c);
}
// Auxiliary method used in process_flex_flex_approx
bool assign_flex_approx(expr const & m, expr const & v, justification const & j, constraint_seq & cs) {
lean_assert(m_config.m_discard);
buffer<expr> args;
expr const & fn = get_app_args(m, args);
lean_assert(is_metavar(fn));
expr type = mlocal_type(fn);
type = ensure_sufficient_args(type, args.size(), cs);
buffer<expr> locals;
for (expr const & a : args) {
expr local = is_local(a) ? a : mk_local_for(type);
locals.push_back(local);
type = instantiate(binding_body(type), local);
}
return assign(m, fn, locals, v, j);
}
bool process_flex_flex_approx(constraint const & c) {
lean_assert(m_config.m_discard);
// Try to solve constraint
// ?M_1 t_1 ... t_n =?= ?M_2 s_1 ... s_m
// by creating a fresh metavariable ?M using common local constants.
// If can't build approximate solution, then discard constraint.
expr const & lhs = cnstr_lhs_expr(c);
expr const & rhs = cnstr_rhs_expr(c);
buffer<expr> lhs_args, rhs_args;
get_app_args(lhs, lhs_args);
get_app_args(rhs, rhs_args);
buffer<expr> shared_locals;
unsigned sz = std::min(lhs_args.size(), rhs_args.size());
unsigned i = 0;
for (; i < sz; i++) {
if (!is_local(lhs_args[i]) || !is_local(rhs_args[i]) ||
mlocal_name(lhs_args[i]) != mlocal_name(rhs_args[i]))
break;
shared_locals.push_back(lhs_args[i]);
}
constraint_seq cs;
if (optional<expr> lhs_type = infer(lhs, cs)) {
expr new_type = Pi(shared_locals, *lhs_type);
if (!has_local(new_type)) {
expr new_mvar = mk_metavar(m_ngen.next(), new_type);
expr new_val = mk_app(new_mvar, shared_locals);
justification const & j = c.get_justification();
return
assign_flex_approx(lhs, new_val, j, cs) &&
assign_flex_approx(rhs, new_val, j, cs) &&
process_constraints(cs, c.get_justification());
}
}
// Failed to generate approximate solution.
// TODO(Leo): generate an error, or just ingore?
// we are currently just ignoring...
return true;
}
bool process_flex_flex(constraint const & c) {
expr const & lhs = cnstr_lhs_expr(c);
expr const & rhs = cnstr_rhs_expr(c);
@ -1979,9 +2041,13 @@ struct unifier_fn {
// ?M_1 l_1 ... l_k =?= ?M_2 l_1 ... l_k ... l_n
// ?M_1 l_1 ... l_k ... l_n =?= ?M_2 l_1 ... l_k
if (!is_simple_meta(lhs) || !is_simple_meta(rhs)) {
if (m_config.m_discard) {
return process_flex_flex_approx(c);
} else {
discard(c);
return true;
}
}
buffer<expr> lhs_args, rhs_args;
expr ml = get_app_args(lhs, lhs_args);
expr mr = get_app_args(rhs, rhs_args);

6
tests/lean/626a.lean.expected.out
View file

@ -1,6 +1,3 @@
626a.lean:3:29: error: don't know how to synthesize placeholder
c : C¹
⊢ nat → Type
626a.lean:3:42: error: don't know how to synthesize placeholder
c : C¹
⊢ ?M_1
@ -12,9 +9,6 @@ c : C¹
remark: set 'formatter.hide_full_terms' to false to see the complete term
λ (c : C¹),
nat.rec_on c ?M_2 ?M_3
626a.lean:8:29: error: don't know how to synthesize placeholder
c : C¹
⊢ C¹ → Type
626a.lean:8:42: error: don't know how to synthesize placeholder
c : C¹
⊢ ?M_1

15
tests/lean/626c.lean.expected.out
View file

@ -1,6 +1,3 @@
626c.lean:2:27: error: don't know how to synthesize placeholder
c : C⁽
⊢ C⁽ → Type
626c.lean:2:40: error: don't know how to synthesize placeholder
c : C⁽
⊢ ?M_1
@ -12,9 +9,6 @@ c : C⁽
remark: set 'formatter.hide_full_terms' to false to see the complete term
λ (c : C⁽),
nat.rec_on c ?M_2 ?M_3
626c.lean:5:27: error: don't know how to synthesize placeholder
c : α⁽
⊢ α⁽ → Type
626c.lean:5:40: error: don't know how to synthesize placeholder
c : α⁽
⊢ ?M_1
@ -26,9 +20,6 @@ c : α⁽
remark: set 'formatter.hide_full_terms' to false to see the complete term
λ (c : α⁽),
nat.rec_on c ?M_2 ?M_3
626c.lean:8:27: error: don't know how to synthesize placeholder
c : _⁽
⊢ _⁽ → Type
626c.lean:8:40: error: don't know how to synthesize placeholder
c : _⁽
⊢ ?M_1
@ -40,9 +31,6 @@ c : _⁽
remark: set 'formatter.hide_full_terms' to false to see the complete term
λ (c : _⁽),
nat.rec_on c ?M_2 ?M_3
626c.lean:11:28: error: don't know how to synthesize placeholder
c : C.⁽
⊢ C.⁽ → Type
626c.lean:11:41: error: don't know how to synthesize placeholder
c : C.⁽
⊢ ?M_1
@ -54,9 +42,6 @@ c : C.⁽
remark: set 'formatter.hide_full_terms' to false to see the complete term
λ (c : C.⁽),
nat.rec_on c ?M_2 ?M_3
626c.lean:14:29: error: don't know how to synthesize placeholder
c : C⁽C⁽
⊢ C⁽C⁽ → Type
626c.lean:14:42: error: don't know how to synthesize placeholder
c : C⁽C⁽
⊢ ?M_1

46
tests/lean/run/662.lean Normal file
View file

@ -0,0 +1,46 @@
open nat
inductive type : Type :=
| Nat : type
| Func : type → type → type
open type
section var
variable {var : type → Type}
inductive term : type → Type :=
| Var : ∀ {t}, var t → term t
| Const : nat → term Nat
| Plus : term Nat → term Nat → term Nat
| Abs : ∀ {dom ran}, (var dom → term ran) → term (Func dom ran)
| App : ∀ {dom ran}, term (Func dom ran) → term dom → term ran
| Let : ∀ {t1 t2}, term t1 → (var t1 → term t2) → term t2
end var
open term
definition Term t := Π (var : type → Type), @term var t
open unit
definition count_vars : Π {t : type}, @term (λ x, unit) t -> nat
| count_vars (Var _) := 1
| count_vars (Const _) := 0
| count_vars (Plus e1 e2) := count_vars e1 + count_vars e2
| count_vars (Abs e1) := count_vars (e1 star)
| count_vars (App e1 e2) := count_vars e1 + count_vars e2
| count_vars (Let e1 e2) := count_vars e1 + count_vars (e2 star)
definition var (t : type) : @term (λ x, unit) t :=
Var star
example : count_vars (App (App (var (Func Nat (Func Nat Nat))) (var Nat)) (var Nat)) = 3 :=
rfl
definition count_vars2 : Π {t : type}, @term (λ x, unit) t -> nat
| _ (Var _) := 1
| _ (Const _) := 0
| _ (Plus e1 e2) := count_vars2 e1 + count_vars2 e2
| _ (Abs e1) := count_vars2 (e1 star)
| _ (App e1 e2) := count_vars2 e1 + count_vars2 e2
| _ (Let e1 e2) := count_vars2 e1 + count_vars2 (e2 star)