Fix Float.parse to handle numbers of the form "-0.x", fixes issue #1960

[justinj]

Fix for #1960, this is my first non-documentation PR to Elixir, so any feedback on how it could be improved would be appreciated :)

Since Float.parse uses Integer.parse, the -0 would be parsed independently of what came after the decimal point and would become 0.

[meh]

Personally I would just have added a head for "-" <> rest and done parse(rest) instead of checking for -0..

[justinj]

I considered that, but that makes this test fail:

assert Float.parse("--1.2") === :error

[ericmj]

@justinj I agree with @meh. Wth a slight modification it can work for your case as well. After matching "-" <> rest, instead of recursing down into parse(rest), call parse_unsign(rest) that should do the rest of the parsing.

See https://github.com/ericmj/decimal/blob/d4a0eb028f65c158fa8cb811492e0b06a70d7705/lib/decimal.ex#L993 for an example .

[justinj]

Thanks a lot for the link @ericmj, how does this look?

[ericmj]

@justinj Perfect 👍

[josevalim]

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