Timeline for Setting nested optional argument with a default when unpacking from a given Head
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 25, 2020 at 11:37 | comment | added | Joe Bentley | Thanks, this looks good, although I probably won't end up using it due to its verbosity :) I'm using Mathematica 12.1.0.0 for reference | |
| Mar 25, 2020 at 11:35 | vote | accept | Joe Bentley | ||
| Mar 24, 2020 at 20:58 | comment | added | Mr.Wizard |
Thanks. On the second point where does a naive Replace[defalt, pattern | _ :> RHS] type of construct fail? Is it in handling multiple arguments? E.g. Replace[g[10], y : (g[x_] | _) :> {y, x}] and Replace[{1, 2, 3}, y : (g[x_] | _) :> {y, x}] both fill {y, x} in what to me seams a reasonable way.
|
|
| Mar 24, 2020 at 19:16 | comment | added | Itai Seggev | Re (1) I'm not sure if this is documented. I'll put it on my doc review list to check. (2) I don't have a great answer for this. It is most likely possible in principle, though there is a question of whether the cost and risk is justified. One thing we did discover when this came up was even in the old code, if the pattern was sufficiently complicated, we might not get all the inner bindings correct (oops). Never doing it is certainly easier to implement, and it is much better to document "never" than "sometimes but we won't tell you when". | |
| Mar 24, 2020 at 6:45 | comment | added | Mr.Wizard | (1) This is a potentially code-breaking change; is it documented? The relaxation was raised in (108636) and it made sense to me at the time, but I hadn't realized what was lost. (2) What is the reason that the pattern binding cannot happen when the default does match? That would seem to be the best of both worlds, without giving this the thought it is probably due. | |
| Mar 24, 2020 at 6:36 | comment | added | Itai Seggev |
You're right, it did change. Probably in 10.x? I'd have go testing versions to be sure. In earlier versions, it was required that the default value match the pattern. It was often requested that we relax this requirement. When we did so, we lost the ability to bind x_ to the default. Based on the number of complaints we've gotten about the change, I think we made the right call with this compromise, but there are edge cases like this one where it is somewhat unfortunate.
|
|
| Mar 24, 2020 at 6:14 | comment | added | Mr.Wizard |
Am I right in thinking that this behavior has changed? I think in version 7 the x_ in f[y:g[x_]:g[10]] := {y, x}; did bind to 10?
|
|
| Mar 24, 2020 at 5:36 | history | answered | Itai Seggev | CC BY-SA 4.0 |