Add logic operations

src/lisp/drawl.pla

@@ -552,6 +552,24 @@ def natv_eq(expr)
   return eval_pred(eval_expr(expr=>car) == eval_expr(expr=>cdr=>car))
 end
 
+def natv_not(expr)
+  return eval_pred(eval_expr(expr=>car) == @pred_false)
+end
+
+def natv_and(expr)
+  while (expr and eval_expr(expr=>car) == @pred_true)
+    expr = expr=>cdr
+  loop
+  return eval_pred(!expr)
+end
+
+def natv_or(expr)
+  while (expr and eval_expr(expr=>car) == @pred_false)
+    expr = expr=>cdr
+  loop
+  return eval_pred(expr)
+end
+
 def natv_cons(expr)
   var consptr
 
@@ -748,6 +766,9 @@ def install_defaults#0
   new_sym("CONS")=>natv   = @natv_cons)
   new_sym("ATOM")=>natv   = @natv_atom)
   new_sym("EQ")=>natv     = @natv_eq)
+  new_sym("NOT")=>natv    = @natv_not)
+  new_sym("AND")=>natv    = @natv_and)
+  new_sym("OR")=>natv     = @natv_or)
   new_sym("COND")=>natv   = @natv_cond)
   new_sym("SET")=>natv    = @natv_set)
   new_sym("SETQ")=>natv   = @natv_setq)