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/common.scm

@@ -0,0 +1,50 @@
+;;; Guile Lua --- common lua functionality
+
+;;; 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 common)
+
+  #:use-module (ice-9 format)
+
+  #:export (syntax-error or-eqv?))
+
+(define (syntax-error src string . arguments)
+  "Throw an error tagged with 'lua-syntax, and print detailed source
+code information when available. STRING and ARGUMENTS are given to FORMAT."
+  (throw 'lua-syntax
+         (string-append
+          (if src
+              (format #f "~a@~a.~a"
+                      (cdr (assq 'filename src))
+                      (cdr (assq 'line src))
+                      (if (assq 'column src)
+                          (cdr (assq 'column src))
+                          "[no column available]"))
+              "[no source code information given]")
+          ": "
+          (apply format (cons string arguments)))))
+
+;; I was using CASE, but this is more succinct
+;; (or-eqv? 1 #f 1) => (or (eqv? 1 #f) (eqv? 1 1))
+(define-syntax or-eqv?
+  (syntax-rules ()
+    ((_ test '(value ...))
+     (or (eqv? test 'value) ...))
+    ((_ test value ...)
+     (or (eqv? test value) ...))))