Parse the given JSON string.

Errors come straight from elm/parser and may not be super useful. It may be worth changing this parser to use elm/parser's Parser.Advanced which allows more control over errors.

Custom type for JSON values.

Mostly this is self-explanatory, but numbers might be interesting because no effort is made to convert them to Float values. This means you can deal with overflows or precision mismatches in broken JSON.

Does the number have a fractional component?

i.e. the optional part after the decimal point.

Does the number have an exponent?

i.e. an optional suffix starting with e or E in the number.

The sign of the exponent.