add lua language implementation

What is missing:

+ Functions: module, getfenv, setfenv, math.modf, table.sort

+ Parser: needs to be more flexible

+ Compiler: needs more extensive work to properly handle all possible
cases of variable arguments, multiple returns, and loops

+ Language: Variable arguments and unpacking of multiple returns. (For
example we need to be able to handle something as complex as
print(unpack({...})), which is easy with Lua's explicit stack but will
require lots of tree-il gymnastics, or perhaps modifications to better
allow different calling conventions. (For instance -- how would we
support Python or Ruby, where keyword arguments are gathered into a
hashtable and passed as a single argument?)

What is there:

A fair shot at supporting Lua 5.1, not quite a drop-in replacement, but
not far from that goal either.

module/language/lua/spec.scm

@@ -0,0 +1,33 @@
+;;; Guile Lua --- language specification
+
+;;; Copyright (C) 2010 Free Software Foundation, Inc.
+;;;
+;;; This library is free software; you can redistribute it and/or
+;;; modify it under the terms of the GNU Lesser General Public
+;;; License as published by the Free Software Foundation; either
+;;; version 3 of the License, or (at your option) any later version.
+;;;
+;;; This library is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public
+;;; License along with this library; if not, write to the Free Software
+;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+;;; Code:
+
+(define-module (language lua spec)
+  #:use-module (system base language)
+  #:use-module (language lua parser)
+  #:use-module (language lua compile-tree-il)
+  #:export (lua))
+
+(define-language lua
+  #:title "Lua"
+  #:reader (lambda (port _)
+             (if (file-port? port)
+                 (read-lua port)))
+  #:compilers `((tree-il . ,compile-tree-il))
+  #:printer write)