diff --git a/src/nasal.h b/src/nasal.h
index 5b6b104..ad651b5 100644
--- a/src/nasal.h
+++ b/src/nasal.h
@@ -8,6 +8,7 @@
 #include <iostream>
 #include <fstream>
 #include <cstring>
+#include <sstream>
 #include <cmath>
 
 // abbreviation of some useful basic type
diff --git a/src/nasal_codegen.cpp b/src/nasal_codegen.cpp
index 5be79a4..e82044a 100644
--- a/src/nasal_codegen.cpp
+++ b/src/nasal_codegen.cpp
@@ -1303,7 +1303,7 @@ void codegen::print(std::ostream& out) {
             out << std::hex << "<0x" << func_begin_stack.top() << std::dec << ">;\n";
             // avoid two empty lines
             if (c.op!=op_newf) {
-                out<<"\n";
+                out << "\n";
             }
             func_begin_stack.pop();
             func_end_stack.pop();
@@ -1322,7 +1322,7 @@ void codegen::print(std::ostream& out) {
         }
 
         // output bytecode
-        out << "  " << codestream(c,i) << "\n";
+        out << "  " << codestream(c, i) << "\n";
     }
 }
 
diff --git a/src/nasal_import.cpp b/src/nasal_import.cpp
index 3a5c2cf..f5b31f0 100644
--- a/src/nasal_import.cpp
+++ b/src/nasal_import.cpp
@@ -198,8 +198,10 @@ code_block* linker::import_regular_file(call_expr* node) {
         return new code_block({0, 0, 0, 0, filename});
     }
     if (check_self_import(filename)) {
-        err.err("link", "self-referenced module <" + filename + ">:\n" +
-            "    reference path: " + generate_self_import_path(filename));
+        err.err("link",
+            "self-referenced module <" + filename + ">:\n" +
+            "    reference path: " + generate_self_import_path(filename)
+        );
         return new code_block({0, 0, 0, 0, filename});
     }
     exist(filename);
@@ -208,16 +210,19 @@ code_block* linker::import_regular_file(call_expr* node) {
     // start importing...
     if (lex.scan(filename).geterr()) {
         err.err("link", "error occurred when analysing <" + filename + ">");
+        return new code_block({0, 0, 0, 0, filename});
     }
     if (par.compile(lex).geterr())  {
         err.err("link", "error occurred when analysing <" + filename + ">");
+        return new code_block({0, 0, 0, 0, filename});
     }
-    auto tmp = par.swap(nullptr);
 
-    // check if tmp has 'import'
-    auto res = load(tmp, find(filename));
+    auto parse_result = par.swap(nullptr);
+
+    // check if parse result has 'import'
+    auto result = load(parse_result, find(filename));
     module_load_stack.pop_back();
-    return res;
+    return result;
 }
 
 code_block* linker::import_nasal_lib() {
@@ -239,16 +244,18 @@ code_block* linker::import_nasal_lib() {
         err.err("link",
             "error occurred when analysing library <" + filename + ">"
         );
+        return new code_block({0, 0, 0, 0, filename});
     }
     if (par.compile(lex).geterr())  {
         err.err("link",
             "error occurred when analysing library <" + filename + ">"
         );
+        return new code_block({0, 0, 0, 0, filename});
     }
-    auto tmp = par.swap(nullptr);
 
-    // check if tmp has 'import'
-    return load(tmp, find(filename));
+    auto parse_result = par.swap(nullptr);
+    // check if library has 'import' (in fact it should not)
+    return load(parse_result, find(filename));
 }
 
 std::string linker::generate_module_name(const std::string& file_path) {
diff --git a/src/optimizer.h b/src/optimizer.h
index 3c33453..4a1d6a6 100644
--- a/src/optimizer.h
+++ b/src/optimizer.h
@@ -7,7 +7,7 @@
 
 namespace nasal {
 
-class optimizer:public ast_visitor {
+class optimizer: public ast_visitor {
 private:
     void const_string(binary_operator*, string_literal*, string_literal*);
     void const_number(binary_operator*, number_literal*, number_literal*);
diff --git a/src/symbol_finder.h b/src/symbol_finder.h
index 3114179..aa7b0cf 100644
--- a/src/symbol_finder.h
+++ b/src/symbol_finder.h
@@ -9,7 +9,7 @@
 
 namespace nasal {
 
-class symbol_finder:public ast_visitor {
+class symbol_finder: public ast_visitor {
 public:
     struct symbol_info {
         std::string name;