Decimal Literals

[jmaessen@alum.mit.edu]

Ketil Z. Malde <ketil@ii.uib.no> writes:
> I.e. for 3.14, allow any rational number in [3.14,3.15), or
> perhaps (3.135,3.145]?  Or restrict it to just the rational number in
> range with the least total digits?

We can get this effect using a version of (%) adapted specifically for
converting decimal floating-point constants.  Thus:

Data.Ratio> 31415926536%1000000000
3926990817 % 125000000

Data.Ratio> let n %% d = approxRational (n%d) (1%(2*d)) in
                31415926536 %% 10000000000
312689 % 99532

We can imagine the compiler replacing floating constants by
fromRational (n%%d) rather than fromRational (n%d).

Of course, then trailing zeros suddenly become significant:

Data.Ratio> let n %% d = approxRational (n%d) (1%(2*d)) in  314 %% 100
22 % 7
Data.Ratio> let n %% d = approxRational (n%d) (1%(2*d)) in  3140 %% 1000
135 % 43

This might be good or bad, depending on your perspective.

-Jan-Willem Maessen
jmaessen@alum.mit.edu