feat(frontends/lean): allow parameters to be used in sections

Restriction:
- coercions and notations cannot be defined in parametric sections

closes #401

src/frontends/lean/builtin_cmds.cpp

@@ -537,8 +537,9 @@ environment open_cmd(parser & p) { return open_export_cmd(p, true); }
 environment export_cmd(parser & p) { return open_export_cmd(p, false); }
 
 environment coercion_cmd(parser & p) {
-    if (in_context(p.env()))
-        throw parser_error("invalid 'coercion' command, coercions cannot be defined in contexts", p.pos());
+    if (in_context_or_parametric_section(p))
+        throw parser_error("invalid 'coercion' command, coercions cannot be defined in contexts or "
+                           "sections containing parameters", p.pos());
     bool persistent = false;
     parse_persistent(p, persistent);
     name f   = p.check_constant_next("invalid 'coercion' command, constant expected");

src/frontends/lean/decl_cmds.cpp

@@ -116,7 +116,7 @@ static environment declare_var(parser & p, environment env,
     if (_bi) bi = *_bi;
     if (k == variable_kind::Parameter || k == variable_kind::Variable) {
         if (k == variable_kind::Parameter) {
-            check_in_context(p);
+            check_in_context_or_section(p);
             check_parameter_type(p, n, type, pos);
         }
         if (p.get_local(n))
@@ -124,7 +124,10 @@ static environment declare_var(parser & p, environment env,
                                << n << "' has already been declared", pos);
         name u = p.mk_fresh_name();
         expr l = p.save_pos(mk_local(u, n, type, bi), pos);
-        p.add_local_expr(n, l, k == variable_kind::Variable);
+        if (k == variable_kind::Parameter)
+            p.add_parameter(n, l);
+        else
+            p.add_local_expr(n, l, k == variable_kind::Variable);
         return env;
     } else {
         lean_assert(k == variable_kind::Constant || k == variable_kind::Axiom);
@@ -162,10 +165,9 @@ static void check_variable_kind(parser & p, variable_kind k) {
         if (k == variable_kind::Axiom || k == variable_kind::Constant)
             throw parser_error("invalid declaration, 'constant/axiom' cannot be used in contexts",
                                p.pos());
-    } else {
-        if (k == variable_kind::Parameter)
-            throw parser_error("invalid declaration, 'parameter/hypothesis/conjecture' "
-                               "can only be used in contexts", p.pos());
+    } else if (!in_section(p.env()) && !in_context(p.env()) && k == variable_kind::Parameter) {
+        throw parser_error("invalid declaration, 'parameter/hypothesis/conjecture' "
+                           "can only be used in contexts and sections", p.pos());
     }
 }
 

src/frontends/lean/notation_cmd.cpp

@@ -629,6 +629,7 @@ struct notation_modifiers {
 };
 
 static environment notation_cmd_core(parser & p, bool overload, bool reserve) {
+    check_not_in_parametric_section(p);
     notation_modifiers mods;
     mods.parse(p);
     flet<bool> set_allow_local(g_allow_local, in_context(p.env()) || !mods.m_persistent);
@@ -642,6 +643,7 @@ static environment notation_cmd_core(parser & p, bool overload, bool reserve) {
 }
 
 static environment mixfix_cmd(parser & p, mixfix_kind k, bool overload, bool reserve) {
+    check_not_in_parametric_section(p);
     notation_modifiers mods;
     mods.parse(p);
     flet<bool> set_allow_local(g_allow_local, in_context(p.env()) || !mods.m_persistent);

src/frontends/lean/parser.cpp

@@ -104,6 +104,7 @@ parser::parser(environment const & env, io_state const & ios,
     m_scanner(strm, strm_name, s ? s->m_line : 1),
     m_theorem_queue(*this, num_threads > 1 ? num_threads - 1 : 0),
     m_snapshot_vector(sv), m_info_manager(im), m_cache(nullptr), m_index(nullptr) {
+    m_has_params = false;
     m_keep_theorem_mode = tmode;
     if (s) {
         m_local_level_decls  = s->m_lds;
@@ -438,7 +439,8 @@ void parser::push_local_scope(bool save_options) {
     optional<options> opts;
     if (save_options)
         opts = m_ios.get_options();
-    m_parser_scope_stack = cons(parser_scope_stack_elem(opts, m_level_variables, m_variables, m_include_vars, m_undef_ids.size()),
+    m_parser_scope_stack = cons(parser_scope_stack_elem(opts, m_level_variables, m_variables, m_include_vars,
+                                                        m_undef_ids.size(), m_has_params),
                                 m_parser_scope_stack);
 }
 
@@ -457,6 +459,7 @@ void parser::pop_local_scope() {
     m_level_variables    = s.m_level_variables;
     m_variables          = s.m_variables;
     m_include_vars       = s.m_include_vars;
+    m_has_params         = s.m_has_params;
     m_undef_ids.shrink(s.m_num_undef_ids);
     m_parser_scope_stack = tail(m_parser_scope_stack);
 }
@@ -481,6 +484,12 @@ void parser::add_local_expr(name const & n, expr const & p, bool is_variable) {
     }
 }
 
+void parser::add_parameter(name const & n, expr const & p) {
+    lean_assert(is_local(p));
+    add_local_expr(n, p, false);
+    m_has_params = true;
+}
+
 unsigned parser::get_local_level_index(name const & n) const {
     return m_local_level_decls.find_idx(n);
 }

src/frontends/lean/parser.h

@@ -53,9 +53,11 @@ struct parser_scope_stack_elem {
     name_set           m_variables;
     name_set           m_include_vars;
     unsigned           m_num_undef_ids;
+    bool               m_has_params;
     parser_scope_stack_elem(optional<options> const & o, name_set const & lvs, name_set const & vs, name_set const & ivs,
-                            unsigned num_undef_ids):
-        m_options(o), m_level_variables(lvs), m_variables(vs), m_include_vars(ivs), m_num_undef_ids(num_undef_ids) {}
+                            unsigned num_undef_ids, bool has_params):
+        m_options(o), m_level_variables(lvs), m_variables(vs), m_include_vars(ivs),
+        m_num_undef_ids(num_undef_ids), m_has_params(has_params) {}
 };
 typedef list<parser_scope_stack_elem> parser_scope_stack;
 
@@ -97,6 +99,7 @@ class parser {
     scanner::token_kind     m_curr;
     local_level_decls       m_local_level_decls;
     local_expr_decls        m_local_decls;
+    bool                    m_has_params; // true context context contains parameters
     name_set                m_level_variables;
     name_set                m_variables; // subset of m_local_decls that is marked as variables
     name_set                m_include_vars; // subset of m_local_decls that is marked as include
@@ -383,7 +386,9 @@ public:
     bool has_locals() const { return !m_local_decls.empty() || !m_local_level_decls.empty(); }
     void add_local_level(name const & n, level const & l, bool is_variable = false);
     void add_local_expr(name const & n, expr const & p, bool is_variable = false);
+    void add_parameter(name const & n, expr const & p);
     void add_local(expr const & p) { return add_local_expr(local_pp_name(p), p); }
+    bool has_params() const { return m_has_params; }
     bool is_local_decl(expr const & l) const { return is_local(l) && m_local_decls.contains(local_pp_name(l)); }
     bool is_local_level_variable(name const & n) const { return m_level_variables.contains(n); }
     bool is_local_variable(name const & n) const { return m_variables.contains(n); }

src/frontends/lean/util.cpp

@@ -40,9 +40,29 @@ void check_in_context(parser const & p) {
     if (!in_context(p.env()))
         throw exception(sstream() << "invalid command, it must be used in a (local) context");
 }
+
+void check_in_context_or_section(parser const & p) {
+    if (!in_context(p.env()) && !in_section(p.env()))
+        throw exception(sstream() << "invalid command, it must be used in a (local) context or section");
+}
+
+bool in_parametric_section(parser const & p) {
+    return in_section(p.env()) && p.has_params();
+}
+
+void check_not_in_parametric_section(parser const & p) {
+    if (in_parametric_section(p))
+        throw exception(sstream() << "invalid command, it cannot be used in sections containing parameters");
+}
+
+bool in_context_or_parametric_section(parser const & p) {
+    return in_context(p.env()) || in_parametric_section(p);
+}
+
 bool is_root_namespace(name const & n) {
     return n == get_root_tk();
 }
+
 name remove_root_prefix(name const & n) {
     return n.replace_prefix(get_root_tk(), name());
 }

src/frontends/lean/util.h

@@ -21,6 +21,10 @@ bool parse_persistent(parser & p, bool & persistent);
 
 void check_atomic(name const & n);
 void check_in_context(parser const & p);
+void check_in_context_or_section(parser const & p);
+void check_not_in_parametric_section(parser const & p);
+bool in_parametric_section(parser const & p);
+bool in_context_or_parametric_section(parser const & p);
 bool is_root_namespace(name const & n);
 name remove_root_prefix(name const & n);
 /** \brief Return the local levels in \c ls that are not tagged as variables.

tests/lean/bad_coercions.lean.expected.out

@@ -1,2 +1,2 @@
 bad_coercions.lean:12:18: error: invalid '[coercion]' modifier, coercions cannot be defined in contexts
-bad_coercions.lean:18:11: error: invalid 'coercion' command, coercions cannot be defined in contexts
+bad_coercions.lean:18:11: error: invalid 'coercion' command, coercions cannot be defined in contexts or sections containing parameters

tests/lean/run/section5.lean

@@ -0,0 +1,18 @@
+section foo
+  parameter A : Type
+  variable a : A
+  definition foo := a
+
+  check foo
+
+  structure point [class] :=
+  (x : A) (y : A)
+end foo
+
+check foo
+
+definition point_nat [instance] : point nat :=
+point.mk nat.zero nat.zero
+
+print classes
+check point