[Nix-dev] isFloat

[Игорь Пашев]

OMG :-) Thank you. I didn't know about regexes. Now we are saved!
29 дек. 2015 г. 23:38 пользователь "Harald van Dijk" <harald at gigawatt.nl>
написал:

> On 29/12/2015 13:20, Игорь Пашев wrote:
> > Is anybody needs floats in options :-)
> >
> >    isFloat = x: isInt x ||
> >        ( isString x &&
> >          3 > length (splitString "." x) &&
> >          all (s: 2 == length (splitString s " 0123456789. "))
> > (stringToCharacters x)
> >        );
>
> Nice. Here are some corner cases to consider though :)
>
>   isFloat (sub 0 1) -> true
> yet
>   isFloat (toString (sub 0 1)) -> false
>
>   isFloat "" -> true
>   isFloat ".." -> true
>   isFloat "1.2." -> true
>   isFloat "1 2" -> true
>
> How about this alternative using a regex?
>
>   isFloat = x: with builtins;
>     match "-?([0-9]+(\\.[0-9]*)?|\\.[0-9]+)" (toString x) != null;
>
> This assumes "1" is valid, "1.1" is valid, "1." is valid, ".1" is valid,
> but plain "." is invalid. It allows an optional leading minus sign
> regardless of whether the argument is an integer or a string. It doesn't
> allow any spaces, not even leading or trailing spaces.
>
> If the precise syntax of allowable floating point numbers changes, for
> instance if "." must always be followed by a digit, if a leading "+" is
> also allowed, if exponential notation ("1E10") is supposed to be allowed,
> if some spaces should be allowed, etc., it can be tweaked fairly easily.
>
> Cheers,
> Harald van Dijk
>
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