feat(frontends/lean): allow user to import several theories using a single import

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/builtin/kernel.lean

@@ -1,8 +1,7 @@
 -- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
 -- Released under Apache 2.0 license as described in the file LICENSE.
 -- Author: Leonardo de Moura
-import macros
-import tactic
+import macros tactic
 
 universe U ≥ 1
 definition TypeU := (Type U)

src/builtin/num.lean

@@ -1,9 +1,7 @@
 -- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
 -- Released under Apache 2.0 license as described in the file LICENSE.
 -- Author: Leonardo de Moura
-import macros
-import subtype
-import tactic
+import macros subtype tactic
 using subtype
 
 namespace num

src/builtin/optional.lean

@@ -1,8 +1,7 @@
 -- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
 -- Released under Apache 2.0 license as described in the file LICENSE.
 -- Author: Leonardo de Moura
-import macros
-import subtype
+import macros subtype
 using subtype
 -- We are encoding the (optional A) as a subset of A → Bool where
 --   none     is the predicate that is false everywhere

src/builtin/sum.lean

@@ -1,9 +1,7 @@
 -- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
 -- Released under Apache 2.0 license as described in the file LICENSE.
 -- Author: Leonardo de Moura
-import macros
-import subtype
-import optional
+import macros subtype optional
 using subtype
 using optional
 

src/frontends/lean/parser_cmds.cpp

@@ -583,26 +583,34 @@ optional<std::string> parser_imp::find_lua_file(std::string const & fname) {
 }
 
 void parser_imp::parse_import() {
+    auto p = pos();
     next();
-    std::string fname;
-    if (curr_is_identifier()) {
-        fname = name_to_file(curr_name());
-        next();
-    } else {
-        fname  = check_string_next("invalid import command, string (i.e., file name) or identifier expected");
-    }
-    bool r = false;
-    if (auto lua_fname = find_lua_file(fname)) {
-        if (!m_script_state)
-            throw parser_error(sstream() << "failed to import Lua file '" << *lua_fname << "', parser does not have an intepreter",
-                               m_last_cmd_pos);
-        r = m_script_state->import_explicit(lua_fname->c_str());
-    } else {
-        r = m_env->import(fname, m_io_state);
-    }
-    if (m_verbose && r) {
-        regular(m_io_state) << "  Imported '" << fname << "'" << endl;
+    unsigned num = 0;
+    while (curr_is_identifier() || curr_is_string()) {
+        std::string fname;
+        if (curr_is_identifier()) {
+            fname = name_to_file(curr_name());
+            next();
+        } else {
+            fname  = curr_string();
+            next();
+        }
+        bool r = false;
+        if (auto lua_fname = find_lua_file(fname)) {
+            if (!m_script_state)
+                throw parser_error(sstream() << "failed to import Lua file '" << *lua_fname << "', parser does not have an intepreter",
+                                   m_last_cmd_pos);
+            r = m_script_state->import_explicit(lua_fname->c_str());
+        } else {
+            r = m_env->import(fname, m_io_state);
+        }
+        if (m_verbose && r) {
+            regular(m_io_state) << "  Imported '" << fname << "'" << endl;
+        }
+        num++;
     }
+    if (num == 0)
+        throw parser_error("invalid import command, string (i.e., file name) or identifier expected", p);
 }
 
 void parser_imp::parse_help() {

src/frontends/lean/parser_imp.h

@@ -165,6 +165,8 @@ public:
 
     /** \brief Return true iff the current token is an identifier */
     bool curr_is_identifier() const { return curr() == scanner::token::Id; }
+    /** \brief Return true iff the current token is a string literal */
+    bool curr_is_string() const { return curr() == scanner::token::StringVal; }
     /** \brief Return true iff the current token is a '_" */
     bool curr_is_placeholder() const { return curr() == scanner::token::Placeholder; }
     /** \brief Return true iff the current token is a natural number */