Change of syntax in WITH-BACKEND.

Using (WITH-BACKEND :BYTECODES form :C/C++ form ...) allows us
to coalesce both possibilities without the output value of
one suppressed form hiding the other one

src/CHANGELOG

@@ -25,10 +25,10 @@ ECL 10.4.2:
    on whether it is going to be processed by the interpreter or by the C
    compiler.
       (defun example ()
-        (ext:with-backend (:bytecodes) (print 3))
-        (ext:with-backend (:c/c++) (print 2)))
-   The two currently available backends are :bytecodes and :c/c++. Note that
-   when the backend does not match the value, the form is replaced with (VALUES).
+        (ext:with-backend
+          :bytecodes (print 3)
+          :c/c++ (print 2)))
+   The two currently available backends are :bytecodes and :c/c++.
 
 
 ECL 10.4.1:

src/c/compiler.d

@@ -1198,10 +1198,14 @@ c_until(cl_env_ptr env, cl_object body, int flags) {
 static int
 c_with_backend(cl_env_ptr env, cl_object args, int flags)
 {
-        cl_object backend = pop(&args);
-        if (!ecl_member_eq(@':bytecodes', backend))
-                args = Cnil;
-        return compile_body(env, args, flags);
+        cl_object forms = Cnil;
+        while (!Null(args)) {
+                cl_object tag = pop(&args);
+                cl_object form = pop(&args);
+                if (tag == @':bytecodes')
+                        forms = CONS(form, forms);
+        }
+        return compile_body(env, forms, flags);
 }
 
 static int

src/cmp/cmpeval.lsp

@@ -137,9 +137,11 @@
   )
 
 (defun c1with-backend (forms)
-  (destructuring-bind ((&rest conditions) &rest body)
-      forms
-    (c1progn (and (member :c/c++ conditions) body))))
+  (c1progn (loop for tag = (pop forms)
+              for form = (pop forms)
+              while tag
+              when (eq tag :c/c++)
+              collect form)))
 
 (defun c1progn (forms)
   (cond ((endp forms) (t1/c1expr 'NIL))

src/new-cmp/cmpspecial.lsp

@@ -29,11 +29,11 @@
     (c1translate `(THE ,type ,destination) value)))
 
 (defun c1with-backend (destination forms)
-  (destructuring-bind ((&rest conditions) &rest body)
-      forms
-    (c1progn destination
-             (and (member :c-backend conditions)
-                  body))))
+  (c1progn destination (loop for tag = (pop forms)
+                          for form = (pop forms)
+                          while tag
+                          when (eq tag :c/c++)
+                          collect form)))
 
 (defun c1compiler-let (destination args &aux (symbols nil) (values nil))
   (when (endp args) (too-few-args 'COMPILER-LET 1 0))