feat(kernel/inductive): add get_num_minor_premises and get_num_type_formers APIs

src/kernel/inductive/inductive.cpp

@@ -971,6 +971,24 @@ optional<unsigned> get_num_indices(environment const & env, name const & n) {
     }
 }
 
+optional<unsigned> get_num_type_formers(environment const & env, name const & n) {
+    if (auto decls = is_inductive_decl(env, n)) {
+        return some(length(std::get<2>(*decls)));
+    } else {
+        return optional<unsigned>();
+    }
+}
+
+optional<unsigned> get_num_minor_premises(environment const & env, name const & n) {
+    inductive_env_ext const & ext = get_extension(env);
+    if (auto it = ext.m_elim_info.find(get_elim_name(n))) {
+        unsigned num_Cs = *get_num_type_formers(env, n);
+        return some(it->m_num_ACe - it->m_num_params - num_Cs);
+    } else {
+        return optional<unsigned>();
+    }
+}
+
 optional<name> is_intro_rule(environment const & env, name const & n) {
     inductive_env_ext const & ext = get_extension(env);
     if (auto it = ext.m_intro_info.find(n))

src/kernel/inductive/inductive.h

@@ -72,6 +72,14 @@ bool is_elim_meta_app(type_checker & tc, expr const & e);
     If \c n is not an inductive datatype in \c env, then return none.
 */
 optional<unsigned> get_num_indices(environment const & env, name const & n);
+/** \brief Return the number of minor premises in the given inductive datatype.
+    If \c n is not an inductive datatype in \c env, then return none.
+*/
+optional<unsigned> get_num_minor_premises(environment const & env, name const & n);
+/** \brief Return the number of type formers in the given inductive datatype.
+    If \c n is not an inductive datatype in \c env, then return none.
+*/
+optional<unsigned> get_num_type_formers(environment const & env, name const & n);
 
 /** \brief Return the eliminator/recursor associated with an inductive datatype */
 name get_elim_name(name const & n);