Surprising return from insert_at

[jdeisenberg]

This surprised me:

insert_at ~index:(-1) ~value:999 [100;101;102;103] = [999]
insert_at ~index:5 ~value:999 [100;101;102;103] = [999]

Looking at the code, this happens because take and drop return the empty list when given values that are out of bounds.

However, I would expect the function to do one of these:

• Return a list the same as the original when given values that are out of bounds, or
• Insert the value at the beginning for negative values, and at the end for values greater than the list length

[pbiggar]

Good point. Let's:

• treat -1 as wrapping, so it inserts in the last position (similar to python)
• if the index is greater than the bounds, put it at the end.

[jdeisenberg]

Treating -1 as wrapping makes things far more difficult, because people would then expect -2, -3... -len(xs) to work in the same way. I think the “do nothing if out of bounds“ is safest and easiest to implement.

[pbiggar]

Good point, let's do that for now then.

[Dean177]

The behaviour of this has now changed.

There is a test case demonstrating that when the index is greater than the length of the list then the value is appended.

The documentation examples still refer to the old behaviour and there is no test case for a negative index.

[pbiggar]

Handled this in #224.

It looks like the wrapping behaviour was supported in the rescript version, so I made native match it, and added tests.

Happy to have done it the other way, this was just easier.