Remove macro NIL

Signed-off-by: yamacir-kit <httperror@404-notfound.jp>

README.md

@@ -105,9 +105,9 @@ sudo rm -rf /usr/local/share/meevax
 
 | Target Name        | Description
 |:-------------------|:--
-| `all` (default)    | Build shared-library `libmeevax.0.4.277.so` and executable `meevax`.
+| `all` (default)    | Build shared-library `libmeevax.0.4.278.so` and executable `meevax`.
 | `test`             | Test executable `meevax`.
-| `package`          | Generate debian package `meevax_0.4.277_amd64.deb`.
+| `package`          | Generate debian package `meevax_0.4.278_amd64.deb`.
 | `install`          | Copy files into `/usr/local` __(1)__.
 | `install.deb`      | `all` + `package` + `sudo apt install <meevax>.deb`
 | `safe-install.deb` | `all` + `test` + `package` + `sudo apt install <meevax>.deb`
@@ -122,7 +122,7 @@ __(1)__ Meevax installed by `make install` cannot be uninstalled by the system's
 ## Usage
 
 ```
-Meevax Lisp System, version 0.4.277
+Meevax Lisp System, version 0.4.278
 
 Usage: meevax [OPTION...] [FILE...]
 

VERSION

@@ -1 +1 @@
-0.4.277
+0.4.278

include/meevax/kernel/configurator.hpp

@@ -36,9 +36,9 @@ inline namespace kernel
     explicit configurator()
     {}
 
-    IMPORT(environment, evaluate, NIL);
-    IMPORT(environment, load, NIL);
-    IMPORT(environment, read, NIL);
+    IMPORT(environment, evaluate, );
+    IMPORT(environment, load,     );
+    IMPORT(environment, read,     );
 
     template <typename Key>
     using dispatcher = std::unordered_map<Key, std::function<void (const_reference)>>;

include/meevax/kernel/heterogeneous.hpp

@@ -31,8 +31,6 @@
 #include <meevax/utility/demangle.hpp>
 #include <meevax/utility/module.hpp>
 
-#define NIL /* nothing */
-
 namespace meevax
 {
 inline namespace kernel

include/meevax/kernel/reader.hpp

@@ -59,7 +59,7 @@ inline namespace kernel
     explicit reader()
     {}
 
-    IMPORT(Environment, evaluate, NIL);
+    IMPORT(Environment, evaluate, );
 
     using char_type = typename std::istream::char_type;