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feat(frontends/lean/elaborator): improve error message for metavariable in inaccessible position on equation lhs

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Leonardo de Moura 2015-01-13 14:38:25 -08:00
parent e9338669dc
commit 37e852ba61
3 changed files with 121 additions and 29 deletions
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134
src/frontends/lean/elaborator.cpp
View file

@ -19,6 +19,7 @@ Author: Leonardo de Moura
#include "kernel/kernel_exception.h"
#include "kernel/error_msgs.h"
#include "kernel/free_vars.h"
#include "kernel/inductive/inductive.h"
#include "library/coercion.h"
#include "library/placeholder.h"
#include "library/choice.h"
@ -843,10 +844,85 @@ static expr copy_domain(unsigned num, expr const & source, expr const & target)
}
}
enum lhs_meta_kind { None, Accessible, Inaccessible };
/**
\brief Auxiliary function for searching for metavariable (applications) on the left-hand-side (lhs) of equations.
The possible results are:
- None: lhs does not contain meta-variables
- Accessible: lhs contains meta-variable, and it is located in a position considered by the pattern-matcher.
- Inaccessible: lhs contains meta-variable, and it is located in a possible inaccessible/ignored by the pattern-matcher,
or its type also contains meta-variables
\remark If the lhs contains accessible and inaccessible metavariables, an accessible is returned.
*/
static pair<lhs_meta_kind, expr> find_lhs_meta(type_checker & tc, expr const & e) {
if (!has_metavar(e))
return mk_pair(None, expr());
environment const & env = tc.env();
optional<expr> acc, inacc;
std::function<void(expr const &, bool)> visit = [&](expr const & e, bool accessible) {
if (acc || !has_metavar(e)) {
return; // done
} else if (is_inaccessible(e)) {
visit(get_annotation_arg(e), false);
} else if (is_meta(e)) {
if (accessible && !acc) {
expr type = tc.infer(e).first;
if (!has_expr_metavar_strict(type))
acc = e;
else if (!inacc)
inacc = e;
} else if (!accessible && !inacc) {
inacc = e;
}
} else if (is_app(e)) {
if (!accessible) {
visit(app_fn(e), false);
visit(app_arg(e), false);
} else {
buffer<expr> args;
expr const & fn = get_app_args(e, args);
if (is_constant(fn) && inductive::is_intro_rule(env, const_name(fn))) {
name I = *inductive::is_intro_rule(env, const_name(fn));
unsigned num_params = *inductive::get_num_params(env, I);
for (unsigned i = 0; i < num_params; i++)
visit(args[i], false);
for (unsigned i = num_params; i < args.size(); i++)
visit(args[i], accessible);
} else {
visit(fn, false);
for (expr const & arg : args)
visit(arg, false);
}
}
} else if (is_macro(e)) {
for (unsigned i = 0; i < macro_num_args(e); i++)
visit(macro_arg(e, i), false);
} else if (is_binding(e)) {
visit(binding_domain(e), false);
visit(binding_body(e), false);
}
};
buffer<expr> args;
get_app_args(e, args);
for (expr const & arg : args)
visit(arg, true);
if (acc)
return mk_pair(Accessible, *acc);
else if (inacc)
return mk_pair(Inaccessible, *inacc);
else
return mk_pair(None, expr());
}
/**
\brief The left-hand-side of recursive equations may contain metavariables associated with
implicit parameters. This procedure replaces them with fresh local constants.
\remark only "accessible" metavariables are replaced
Example 1)
Suppose we are defining
map : Pi {n}, vec A n -> vec B n -> vec C n,
@ -917,43 +993,43 @@ static expr assign_equation_lhs_metas(type_checker & tc, expr const & eqns) {
unsigned idx = 1;
while (true) {
expr lhs = equation_lhs(eq);
optional<expr> meta;
optional<expr> meta_type;
for_each(lhs, [&](expr const & e, unsigned offset) {
if (meta) return false; // already found target
if (offset > 0) return false;
if (is_meta(e)) {
expr type = tc.infer(e).first;
if (!has_expr_metavar_strict(type)) {
meta = e;
meta_type = type;
return false; // stop search, found
}
}
return has_metavar(e);
});
if (!meta)
auto r = find_lhs_meta(tc, lhs);
if (r.first == None) {
break;
expr new_local = mk_local(tc.mk_fresh_name(), x.append_after(idx), *meta_type, binder_info());
for (expr & local : locals)
local = update_mlocal(local, replace_meta(mlocal_type(local), *meta, new_local));
eq = replace_meta(eq, *meta, new_local);
unsigned i = num_fns;
for (; i < locals.size(); i++) {
if (depends_on(mlocal_type(locals[i]), new_local)) {
break;
} else if (r.first == Accessible) {
expr const & meta = r.second;
expr meta_type = tc.infer(meta).first;
expr new_local = mk_local(tc.mk_fresh_name(), x.append_after(idx), meta_type, binder_info());
for (expr & local : locals)
local = update_mlocal(local, replace_meta(mlocal_type(local), meta, new_local));
eq = replace_meta(eq, meta, new_local);
unsigned i = num_fns;
for (; i < locals.size(); i++) {
if (depends_on(mlocal_type(locals[i]), new_local))
break;
}
locals.insert(i, new_local);
idx++;
} else {
lean_assert(r.first == Inaccessible);
throw_elaborator_exception(eqns, [=](formatter const & fmt) {
options o = fmt.get_options().update_if_undef(get_pp_implicit_name(), true);
o = o.update_if_undef(get_pp_notation_option_name(), false);
formatter new_fmt = fmt.update_options(o);
format r("invalid recursive equation, left-hand-side contains meta-variable");
r += format(" (possible solution: provide implicit parameters occurring in left-hand-side explicitly)");
r += pp_indent_expr(new_fmt, lhs);
return r;
});
}
locals.insert(i, new_local);
idx++;
}
new_eqs.push_back(Fun(locals, eq));
}
}
return update_equations(eqns, new_eqs);
}
// \remark original_eqns is eqns before elaboration
constraint elaborator::mk_equations_cnstr(expr const & m, expr const & eqns) {
bool relax = m_relax_main_opaque;
environment const & _env = env();
@ -1019,9 +1095,9 @@ expr elaborator::visit_equations(expr const & eqns, constraint_seq & cs) {
expr new_eqns;
if (new_R) {
new_eqns = mk_equations(num_fns, new_eqs.size(), new_eqs.data(), *new_R, *new_Hwf);
new_eqns = copy_tag(eqns, mk_equations(num_fns, new_eqs.size(), new_eqs.data(), *new_R, *new_Hwf));
} else {
new_eqns = mk_equations(num_fns, new_eqs.size(), new_eqs.data());
new_eqns = copy_tag(eqns, mk_equations(num_fns, new_eqs.size(), new_eqs.data()));
}
lean_assert(first_eq && is_lambda(*first_eq));

14
tests/lean/unzip_error.lean Normal file
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@ -0,0 +1,14 @@
import data.vector
open nat vector prod
variables {A B : Type}
definition unzip : Π {n : nat}, vector (A × B) n → vector A n × vector B n,
unzip nil := (nil, nil),
unzip ((a, b) :: v) :=
match unzip v with
(va, vb) := (a :: va, b :: vb)
end
example : unzip ((1, 20) :: (2, 30) :: nil) = (1 :: 2 :: nil, 20 :: 30 :: nil) :=
rfl

2
tests/lean/unzip_error.lean.expected.out Normal file
View file

@ -0,0 +1,2 @@
unzip_error.lean:9:2: error: invalid recursive equation, left-hand-side contains meta-variable (possible solution: provide implicit parameters occurring in left-hand-side explicitly)
match (@mk (vector A ?M_1) (vector B ?M_1) va vb)