From f12a8076d00d14b35cf4de0f0649a3cd1e9e0246 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Renaud=20Casenave-P=C3=A9r=C3=A9?= <renaud@casenave-pere.fr>
Date: Wed, 25 Mar 2015 17:37:27 +0100
Subject: [PATCH] Add a simple handler for `let'

---
 src/render/shader/glsl.lisp   | 17 ++++++++++++++++-
 src/render/shader/walker.lisp |  5 +++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/render/shader/glsl.lisp b/src/render/shader/glsl.lisp
index a2b28e5..6dd754e 100644
--- a/src/render/shader/glsl.lisp
+++ b/src/render/shader/glsl.lisp
@@ -21,9 +21,24 @@
 (defvar *current-indent* 0
   "Keep the number of space needed for the next directive.")
 
+(defvar *env* nil
+  "A special variable used as a container for the macro environment.")
+
 (defhandler newshader (newshader lambda-list &rest body)
   (walk-list body))
 
+(defhandler let (let bindings &rest body)
+  (let* ((names (loop for binding in bindings
+                   collect (safe-first binding)))
+         (symbol-macrolet-names (loop for name in names
+                                   when (nth-value 1 (macroexpand-1 name *env*))
+                                   collect name)))
+    (apply #'concatenate 'string
+           (append (loop for binding in bindings
+                      collect (format nil "~(~a ~a~)~@[ = ~a~];~%" (second binding) (first binding)
+                                      (walk-list (cddr binding))))
+                   (walk-list body)))))
+
 (defun default-handler (first &rest rest)
   "Handle a simple function call."
   (format nil "~@[~vt~]~(~a~) (~{~a~^, ~});~%"
@@ -35,4 +50,4 @@
 
 (defun glsl-compile (form)
   (let ((*current-indent* 0))
-    (walk form *form-handlers* #'default-handler)))
+    (walk form *form-handlers* #'default-handler *env*)))
diff --git a/src/render/shader/walker.lisp b/src/render/shader/walker.lisp
index 2cfb874..143b073 100644
--- a/src/render/shader/walker.lisp
+++ b/src/render/shader/walker.lisp
@@ -83,8 +83,9 @@
                     collect `(gethash ',sym ,(intern (symbol-name '*form-handlers*)))
                     collect `',func))))))
 
-(defun walk (form handlers default-handler)
+(defun walk (form handlers default-handler env)
   "Walk the sexp FORM and transform it according to the rules defined in HANDLERS."
   (let ((*form-handlers* handlers)
-        (*default-handler* default-handler))
+        (*default-handler* default-handler)
+        (*env* env))
     (walk-1 form)))