Make `Char.toCode` Roundtrip

[crazymykl]

Synopsis

It's quite surprising that certain Chars cannot be converted to integers and back losslessly.

Open Questions

• I have made Char.fromCode keep its existing behavior when given an Int outside of the range of valid Unicode. Should it be made KeyCode -> Maybe Char instead?

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[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[crazymykl]

This is related to #387.

[crazymykl]

This is related to #387.

[crazymykl]

I spoke with @rtfeldman , and losing O(1) length is a hard-no. I'd still like the functions on Char that convert from keycodes to roundtrip.

[crazymykl]

I spoke with @rtfeldman , and losing O(1) length is a hard-no. I'd still like the functions on Char that convert from keycodes to roundtrip.

[jahewson]

Can a KeyCode actually contain a surrogate pair? As far as I'm aware KeyboardEvent.keyCode generates only ASCII and Windows-1252 characters.

Incidentally, a KeyCode from the Keyboard library is not even guaranteed to be Unicode, it could be Windows-1252. Seems like this could be a broader problem for Elm, which appears to assume that a KeyCode is a Unicode code point, because it mingles Keyboard and Char logic via KeyCode.

I suspect that the whole relationship between KeyCode and Char needs some re-thinking.

[jahewson]

Can a KeyCode actually contain a surrogate pair? As far as I'm aware KeyboardEvent.keyCode generates only ASCII and Windows-1252 characters.

Incidentally, a KeyCode from the Keyboard library is not even guaranteed to be Unicode, it could be Windows-1252. Seems like this could be a broader problem for Elm, which appears to assume that a KeyCode is a Unicode code point, because it mingles Keyboard and Char logic via KeyCode.

I suspect that the whole relationship between KeyCode and Char needs some re-thinking.