Add cons, car and cdr

lib/core.fs

@@ -1,13 +1,6 @@
 \ planckforth -
 \ Copyright (C) 2021 nineties
 
-defined? roll [unless]
-    : roll ( wn ... w1 n -- w1 wn ... w2 )
-        dup 0<= if drop else swap >r 1- recurse r> swap then
-    ;
-[then]
-
-
 \ Ignore test codes. lib/tester.fs will redefine this when
 \ running tests.
 : T{
@@ -22,3 +15,29 @@ s" Invalid argument" exception constant INVALID-ARGUMENT
 : check-argument ( f  -- )
     unless INVALID-ARGUMENT throw then
 ;
+
+defined? roll [unless]
+    : roll ( wn ... w1 n -- w1 wn ... w2 )
+        dup 0<= if drop else swap >r 1- recurse r> swap then
+    ;
+[then]
+
+private{
+
+( === Cons Cell === )
+
+struct
+    cell% field first
+    cell% field second
+end-struct cons-cell%
+
+: cons ( a b  -- cons )
+    cons-cell% %allocate throw
+    tuck second !
+    tuck first !
+; export
+
+: car first @ ; export
+: cdr second @ ; export
+
+}private

test/core.fs

@@ -1003,4 +1003,14 @@ T{ gdx -> 123 234 }T
 
 cr ." End of Core word set tests" cr
 
+\ ------------------------------------------------------------------------
+testing cons, car and cdr
+
+0 1 cons constant cons0
+
+T{ cons0 car -> 0 }T
+T{ cons0 cdr -> 1 }T
+
+cons0 free
+