I just noticed a new form of With in its documentation:

With[$x=x_0$, $expr$]

specifies that all occurrences of the symbol $x$ in $expr$ should be replaced by $x_0$.

Note the lack of braces around first argument. I can see this also in documentation center of v10.2.

But when I try to use it, I get the standard error message, as in previous versions.

With[x = y, x]
(* "10.2.0 for Linux x86 (64-bit) (July 6, 2015)" *)

With::lvlist: Local variable specification x=y is not a List. >>

(* With[x = y, x] *)

Is this another symptom of documentation driven development?

Reported to WRI as [CASE:3390526]

  • 1
    $\begingroup$ @MarcoB on Win7 it appeared in 10.1->10.2 step. $\endgroup$ – Kuba Jul 23 '15 at 9:49
  • 3
    $\begingroup$ It is a curious choice to implement this syntax now. It would have made good sense to do so initially (perhaps along with {a, b, c, ...} = {a0, b0, c0, ...}) for the sake of consistency with other functions, but to leave it until after version 10 seems to be to introduce a backward-compatibility constraint to no real benefit. $\endgroup$ – Oleksandr R. Jul 23 '15 at 10:34
  • 11
    $\begingroup$ That bit of documentation is a bug so feel free to add that tag. One thing this was not is documentation driven development. $\endgroup$ – Daniel Lichtblau Jul 23 '15 at 13:36
  • 5
    $\begingroup$ @Mr.Wizard It was implemented in the development versions of 10.2 for a while, but due to several issues it caused, as well as long internal discussions, it was shelved for the time being. $\endgroup$ – Stefan R Jul 23 '15 at 18:24
  • 5
    $\begingroup$ It's not likely to come back.As noted by @StefanR. it caused actual trouble (conflict with existing evaluation semantics). $\endgroup$ – Daniel Lichtblau Jul 23 '15 at 20:33

This is a documentation bug. Our source notebooks do contain documentation for experimental and future features, but they are supposed to be stripped in the process of being bundled with the product. In this case the bug is that the usage statement is marked as not to be included, but is still ending up in the built documentation.

We apologize for the inconvinience and confusion.


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