Add float.modulo

[dalprahcd]

Should close #525 by adding the float.modulo function.

I also tried implementing the float.remainder function as:

pub fn modulo(dividend: Float, by divisor: Float) -> Result(Float, Nil) {
  case divisor {
    0.0 -> Error(Nil)
    _ -> Ok(dividend -. round(dividend /. divisor) *. divisor)
  }
}

But round returns an Int and I could not find an easy way to convert it back to Float. A little bit off-topic, but why does it return an Int it should return a Float right?

[lpil]

A little bit off-topic, but why does it return an Int it should return a Float right?

If round returned a float how would you round a float to an int?

[lpil]

Thank you!

[lpil]

Can we have fewer examples please? It's a little overwhelming I think

[dalprahcd]

The comments were copied from the int.modulo function, they explain all the possible behaviours.

• When divisor is non-zero and when it is zero.
• That the modulo follows the sign of the divisor.

Can we keep the examples?

[lpil]

There is too much information here, please reduce it. The examples section is not suitable for an exhaustive description of the behaviour.

[lpil]

All of these are whole numbers. Let's have tests for other numbers too.

[dalprahcd]

Done, could you help me solve this failing test?

Failures:

  1) gleam/float_test.modulo_test
     Values were not equal
     expected: Ok(1.3)
          got: Ok(1.3000000000000007)

[inoas]

Check https://hexdocs.pm/gleam_stdlib/gleam/float.html#loosely_equals maybe

[dalprahcd]

Check https://hexdocs.pm/gleam_stdlib/gleam/float.html#loosely_equals maybe

But then I believe I would need to import the result library to unwrap the value before, right? Is it ok adding this dependency?

[dalprahcd]

If round returned a float how would you round a float to an int?

We could explicit convert float to int by implementing int.to_float and float.to_int (if not already implemented). Then we could also expand the float.round function to accept how many decimals places we want to round the float.

Finally, we would have 3 options to round a float to int: float.floor, float.ceiling, float.round(x, 0). And the user would be responsible to choose which one is more suitable.

Calling float.to_int would essentially cut out the decimal places.

[NicklasXYZ]

If round returned a float how would you round a float to an int?

We could explicit convert float to int by implementing int.to_float and float.to_int (if not already implemented). Then we could also expand the float.round function to accept how many decimals places we want to round the float.

Finally, we would have 3 options to round a float to int: float.floor, float.ceiling, float.round(x, 0). And the user would be responsible to choose which one is more suitable.

Calling float.to_int would essentially cut out the decimal places.

This is how I've implemented it in the the community math lib :)
I guess the question is also related to this closed issue: #625 (comment)

[dalprahcd]

Hello @lpil and @inoas, sorry for being away for so long.

I wish to merge this PR, what are the remaining steps?

[lpil]

The comments from my review haven't been addressed yet!

[lpil]

Thank you!