Implicit product for terms ?

[drhodes]

Hi everyone! This is a feature proposal for introducing implicit products for numeric literals adjacent with other expressions, for example:

2x would parse as 2 * x
2sin(x) would parse as 2 * sin(x)

For what it's worth the julia programming language manages to allow this (so perhaps, at least, it's not a bad idea for some unknown reason), but more importantly for users of openedx, forgetting the * character is one of the most common entry mistakes.

[jolyonb]

This is a massive can of worms... The parser is easily the most complicated part of this library, and I'm loathe to change it. We already have excellent error messages if students forget a * character in an expression; I'm not sure this is really worth the effort?

[jolyonb]

Elaborating a bit... Remember that 2e3 is treated as a valid number. How would you handle that in your proposed syntax, especially if e3 is a defined function?

[drhodes]

julia> 2e3
2000.0

julia> 22e3
22000.0

julia> 2222e3
2.222e6

julia just interprets it as a float64.

What about e3 as a defined function? Well..

julia> e3(x) = x^2
e3 (generic function with 1 method)

julia> 2e3(2)
4000.0

I thoroughly understand your concern about the can of worms, what's going to break, for whom, etc..

[jolyonb]

What happens if you also set e3=6 as a variable?

[drhodes]

julia> e4 = 6
6

julia> 2e4
20000.0

[jolyonb]

There we go... I'd really like to avoid something like that happening in the parser.

Another reason I'd like to avoid this is backwards compatibility with edX. Basically, anything that your stock standard edX math input box accepts, we need to handle in exactly the same way (with the sole exception of an order-of-precedence bug in the edX parser regarding exponentials). This hamstrings us somewhat; there are certainly decisions I'd make differently if I could be freed from that constraint. I don't know if it precludes what you're requesting, but it certainly doesn't make it easy.

[drhodes]

Ok Jolyon, thanks for taking time out to consider the issue, I appreciate it!