Julia: Feature request: additional plain text arrow symbols

[isaacsas]

Right now --> parses as a symbol, along with a fantastic number of unicode arrows. It would be nice if we could also have the reversed arrow, <--, and some kind of reversible plaintext arrow like <-> or <-->. We use such notation in the DiffEqBiological DSL for specifying chemical reactions, i.e. A + B --> C, and have had several requests for some type of reversible arrow notation from several users now for whom using a unicode arrow was problematic.

Thanks!

[StefanKarpinski]

Triage agrees that we may as well have some of these and they can parse like other infix arrow operators. It remains for our resident parsing czar to determine which can be parsed unambiguously.

[StefanKarpinski]

It might also make sense to change the parsing of --> to parse as a normal infix operator. For historical reasons, it parses as its own expression head, which is kind of strange.

[JeffBezanson]

<-- and <--> should be ok at least. <-> is probably OK but we can't have <-, since 1<-2 parses as 1 < -2, so it's a bit sketchier.

[isaacsas]

Getting one of <-> or <--> would be great for us and the best gain. <-- is not particularly needed since users can always go the other direction. (It just seemed reasonable to have for symmetry reasons...)

[isaacsas]

Thanks for the help!