Fwd: add instance PrintfArg Ratio

[Dannyu NDos]

---------- Forwarded message ---------
보낸사람: Dannyu NDos <ndospark320 at gmail.com>
Date: 2020년 2월 8일 (토) 오전 8:22
Subject: Re: add instance PrintfArg Ratio
To: Henning Thielemann <lemming at henning-thielemann.de>


In that case, here (with some bugfixes):

instance (Integral a, PrintfArg a) => PrintfArg (Ratio a) where
    formatArg x f@(FieldFormat w p a s l _ c) = if elem c "gGv"
        then let
            d = " % " ++ formatArg (denominator x) (FieldFormat Nothing
Nothing Nothing s l "" 'd') ""
            (w',a') = case a of
                Just LeftAdjust -> (Nothing, Nothing)
                _ -> (fmap (subtract (length d)) w, a)
            n = formatArg (numerator x) (f {fmtWidth = w', fmtAdjust = a',
fmtChar = 'd'}) ""
            in formatArg (n ++ d) (f {fmtPrecision = Nothing, fmtChar =
's'})
        else if elem c "doxXb"
            then formatArg (round x :: Integer) f
            else case p of
                Nothing -> error "Text.Printf.formatArg: precision not
given"
                Just p' -> if p' <= 0
                    then formatArg x (f {fmtPrecision = Nothing, fmtChar =
'd'})
                    else if elem c "fF"
                        then let
                            n = truncate x
                            sig = '.' : goF (x - fromInteger n) p'
                            (w',a') = case a of
                                Just LeftAdjust -> (Nothing, Nothing)
                                _ -> (fmap (subtract (length sig)) w, a)
                            b = formatArg n (FieldFormat w' Nothing a' s l
"" 'd') ""
                            in formatArg (b ++ sig) (f {fmtPrecision =
Nothing, fmtChar = 's'})
                        else if elem c "eE"
                            then let
                                (q,e) = log10 x
                                sig = c : show e
                                (w',a') = case a of
                                    Just LeftAdjust -> (Nothing, Nothing)
                                    _ -> (fmap (subtract (length sig)) w, a)
                                fp = formatArg q (f {fmtWidth = w',
fmtAdjust = a', fmtChar = 'f'}) ""
                                in formatArg (fp ++ sig) (f {fmtPrecision =
Nothing, fmtChar = 's'})
                            else error "Text.Printf.formatArg: bad format
character"
      where
        goF _ 0 = ""
        goF x p = case compare x 0 of
            LT -> '-' : goF (negate x) p
            EQ -> "0"
            GT -> if 1 == p
                then show (round (10 * x) :: Integer)
                else let
                    x10 = 10 * x
                    n = truncate x10
                    in show n ++ goF (x10 - fromIntegral n) (p - 1)
        log10 x
            | x < 1 = let
                (q,e) = log10 (x * 10)
                in (q, e - 1)
            | 10 <= x = let
                (q,e) = log10 (x / 10)
                in (q, e + 1)
            | otherwise = (x, 0)

2020년 2월 8일 (토) 오전 6:44, Henning Thielemann <lemming at henning-thielemann.de>님이
작성:

>
> On Fri, 7 Feb 2020, Dannyu NDos wrote:
>
> > It just is so convenient.
> >
> > instance (Integral a, Show a) => PrintfArg (Ratio a) where
>
> Why should a Printf instance be base on Show? Wouldn't it better to format
> numerator and denominator using printf, too?
>
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