bug in displaying fixed numbers

[Lukasz Pankowski]

I was very surprised when I discovered (writing a bit more complicated
program) that a program like

> import Numeric ( floatToDigits )
> print $ showFFloat Nothing 0.01 ""

enters in to infinite loop. I found that (formatRealFloat FFFixed
Nothing) do not like displaying numbers less than 0.1.
For x = 0.01 we have e=-1 and ds="1". Function f loops down to 0,
which will never be reached.

I changed the function in hugs for my use. But since the problem is in
a standard library I will have to make a workaround for may code to
work elsewhere.

Original and modified parts below. 

Original:
                FFFixed ->
                    case decs of
                    Nothing ->
                        let f 0 s ds = mk0 s ++ "." ++ mk0 ds
                            f n s "" = f (n-1) (s++"0") ""
                            f n s (d:ds) = f (n-1) (s++[d]) ds
                            mk0 "" = "0"
                            mk0 s = s
                        in  f e "" ds


Wish:
                FFFixed ->
                    case decs of
                    Nothing ->
                        let f 0 s ds = mk0 s ++ "." ++ mk0 ds
                            f n s "" = f (n-1) (s++"0") ""
                            f n s (d:ds) = f (n-1) (s++[d]) ds
			    g n ds = "0." ++ (replicate n '0') ++ ds
                            mk0 "" = "0"
                            mk0 s = s
                        in  if e >= 0
			    then f e "" ds
			    else g (-e) ds


I am rather new to Haskell so I do not know if the problem have been
discussed already.

-- 

=*= Lukasz Pankowski =*=