add notes on future functionality

diff --git a/src/lib/unlang/xlat_expr.c b/src/lib/unlang/xlat_expr.c
index ff4650aeb42db4ede31880ab93fc9629159e4c55..c2da1069ba59b7c1e6b72fafa8c9157bd1a88048 100644 (file)
--- a/src/lib/unlang/xlat_expr.c
+++ b/src/lib/unlang/xlat_expr.c
@@ -360,8 +360,8 @@ static xlat_action_t xlat_binary_op(TALLOC_CTX *ctx, fr_dcursor_t *out,
         *      any existing enum alone.
         */
        if (enumv) dst->enumv = enumv;
-
        fr_dcursor_append(out, dst);
+
        VALUE_BOX_LIST_VERIFY((fr_value_box_list_t *)out->dlist);
        return XLAT_ACTION_DONE;
 }
@@ -391,6 +391,55 @@ static xlat_arg_parser_t const binary_cmp_xlat_args[] = {
        XLAT_ARG_PARSER_TERMINATOR
 };
 
+/*
+ *     @todo - arguably this function should process its own arguments, like logical_or.
+ *
+ *     That way it can return XLAT_ACTION_FAIL if either argument fails to be found,
+ *     or if the comparison matches, it returns the RHS value.  This behavior will
+ *     let us to multiple comparisons, like:
+ *
+ *             if (0 < x < 5) ...
+ *
+ *     Which is then syntactic sugar for
+ *
+ *             if ((0 < x) < 5) ...
+ *
+ *     That means the comparisons no longer return "bool", so if we
+ *     want to do this, the change has to be made before v4 is
+ *     released.
+ *
+ *     Other operators like "+=" would return their LHS value.  But in order to do that, we would have to
+ *     update the expression parser to allow in-place edits, and that may be a fair bit of work.
+ *
+ *     It also lets us do more interesting selectors, such as:
+ *
+ *             foo || (0 < x)
+ *
+ *     which if "foo" doesn't exist, evaluates the RHS, and then returns "x" only if x is greater than zero.
+ *     This short-hand can remove a lot of complex / nested "if" conditions.
+ *
+ *     It could also allow us to do better attribute filtering:
+ *
+ *             foo := (0 < foo < 5)
+ *
+ *     Which ensures that "foo" has value only 1..4.
+ *
+ *     It would be nice to have a syntax for "self", so we could instead do:
+ *
+ *             foo := (0 < $$ < 5)
+ *
+ *     Which could then also be used inside of attribute selectors:
+ *
+ *             foreach foo (Vendor-Specific.Cisco.AVPair[$$ =~ /^x/]) { ...
+ *
+ *     and now that we have pair cursors as value-boxes, this becomes a lot easier.
+ *     "$$" then becomes syntactic sugar for "the pair at the current cursor".
+ *
+ *     It also means tracking somehow the value of $$ in the interpreter?  Maybe as a short-hand, just update
+ *     the #request_t to add a #fr_pair_t of the current cursor value.  This is a horrible hack, but would be
+ *     easy to do.  It doesn't allow nested cursors, but whatever.  The syntax for that would be hard to get
+ *     right.
+ */
 static xlat_action_t xlat_cmp_op(TALLOC_CTX *ctx, fr_dcursor_t *out,
                                 UNUSED xlat_ctx_t const *xctx,
                                 UNUSED request_t *request, fr_value_box_list_t *in,