:sig
function f64(value : as string, opt : dval = {}) f64

:params
value : scalar value or text to convert
opt : options map with `fallback`

:returns
An `f64` value, or `opt.fallback`.

:content
`f64()` converts the exact text from `value` to a floating-point value. The value must contain a complete decimal number. `opt.fallback` is the result for empty text or text that does not parse. It defaults to `0.0`.

`value` accepts scalar values through `as string`. The conversion keeps scalar text exact. Empty and missing `dval` values both convert to empty text. Use `value?` before conversion when presence matters. An empty value is present, but a missing value is not.

The options map accepts only `fallback`. An unknown key, including `base`, is an error.

:example capy render
print(f64("3.5"), "\n")
print(f64("not a number", fallback: 9.0), "\n")

:see-group
constructors
