add subtract functions in date-related modules to increase readability?

[Thomas J.]

Hello,

I'm a little surprised for having to use a function named `add` (with a given negative value) to subtract days.

Why not add subtract functions to make the code easier to read?

[Andrea Leopardi]

Hey Thomas,

we usually try to strike a good balance between having as little functions as possible in the standard library (to avoid bloating it) and having enough functions so that your code can be efficient and expressive. In this case, the performance is not different, so adding it would only be a readability concern. Personally, I feel like using "add/2" and negating the second argument is clear enough that it doesn't warrant an additional function to the date-related modules.

Cheers,

Andrea Leopardi

an.le...@gmail.com

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[Manfred Bergmann]

Hi.

I believe in math it’s completely legit to write: 1 + (-1) = 0


Manfred

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[Xavier Noria]

On Fri, Jan 31, 2020 at 5:14 PM 'Manfred Bergmann' via elixir-lang-core <elixir-l...@googlegroups.com> wrote:

Hi.

I believe in math it’s completely legit to write: 1 + (-1) = 0

Yes. Even more, technically the canonical algebraic structure for integers (a ring called Z) has addition and multiplication only. There is a concept of "the opposite of an integer": the opposite of N is a number M such that N + M = 0. By convention, you write "-N" as an alias for said (unique) M, and X - Y is a shortcut for X + (-Y). There is no subtraction operation.

So, your notation is actually quite literally exact.