With the current regexp-based rewriting we'd need a pattern of the kind '<argument>!' -> 'factorial(<argument)'. That will be very tricky to do. We are doing an operator substitution already '^' -> '**" but that's very basic and doesn't need any context. To change an implicit unary postfix operator to an explicitly parenthesized prefix operator need almost complete parsing. Had the factorial been explicitly parenthesized as well, it would be a little easier, since now you could do it with parenthesis counting -- still not regex territory, but possibly reasonably efficiently done if one concentrates on the case where the expected string before the ! is short.
Insisting on parens does not satisfy the people who'd request this, I imagine. Writing (5)! instead of 5! doesn't really do the trick. I consider this weird postfix notation as a peculiarity that works somewhat OK in written math but, just as implicit multiplication, as bad in CAS use. So I'm not in favour of it. I estimate that the number of arguments against it is at least 3! On Sunday, November 29, 2020 at 5:32:30 AM UTC-8 Simon King wrote: > On 2020-11-29, Simon King <simon...@uni-jena.de> wrote: > > Hi Emmanuel, > > > > On 2020-10-28, Emmanuel Charpentier <emanuel.c...@gmail.com> wrote: > >> Nope. This syntactic sugar is provided by `Maxima`'s and > `Mathematica`'s > >> readers, but not by Sage preparser. > > > > Would it be nice (and easy) to have in Sage? What prevents the preparser > > from understanding "!"? > > To be more precise: If I understand correctly, the preparser can be made > to accept any syntax, provided that this syntax is in no conflict with > valid Python syntax. > > There is a special meaning of "?" and "??" in Python, but I think there > isn't a special meaning to "!". Sage accepts "!" at the beginning of a > line, meaning that it executes a shell command, such as > sage: !ls > But it should be possible that the preparser could turn "(expression)!" > into > "gamma(expression+1)". > > Do people agree? Unfortunately I do not volonteer to implement it, I' > not familiar with the innards of the preparser. > > Best regards, > Simon > > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-support/0f70ad8a-bf21-4352-a863-0b8d596e509cn%40googlegroups.com.
