virtual optional<expr> expand(expr const & m, abstract_type_context & ctx) const {
check_macro(m);
expr const & s = macro_arg(m, 0);
expr new_s = ctx.whnf(s);
buffer<expr> c_args;
expr const & c = get_app_args(new_s, c_args);
if (is_constant(c) && const_name(c) == m_constructor_name && m_idx < c_args.size()) {
return some_expr(c_args[m_idx]);
} else {
// expand into recursor
expr s_type = ctx.whnf(ctx.infer(s));
buffer<expr> args;
expr const & I = get_app_args(s_type, args);
if (!is_constant(I) || length(m_ps) != length(const_levels(I)))
return none_expr();
expr r = instantiate_univ_params(m_val, m_ps, const_levels(I));
args.push_back(new_s);
return some(instantiate_rev(r, args.size(), args.data()));
}
}
