[erlang-questions] display floats without -e?

Richard O'Keefe <>
Tue Jan 1 12:11:43 CET 2019


You might want to do some more testing.

11> floaty:auto(12.3455555533).
"12.345555553300000"

It is not clear that this is something you would be happy with.
I discovered this by simplifying the code to

auto(F) when is_float(F) ->
   P = precision(abs(F), 0),
   erlang:float_to_list(F, [{decimals,P}]).

-spec precision(float(), integer()) -> integer().
precision(A, P) ->
    if A == trunc(A) -> P
     ; true          -> precision(A*10.0, P+1)
    end.

and doing some testing of my own.  I was rather relieved to discover
that the original code behaved the same way.

It's really not clear what the aim is here.
I suspect that it is something that should be
done with numbers rather than lists.


On Tue, 1 Jan 2019 at 23:43, PAILLEAU Eric <> wrote:

> Hi,
>
>
> 1> c(floaty).
> {ok,floaty}
> 2> floaty:auto(12.345555).
> "12.345555"
> 3> floaty:auto(12.3455553333333).
> "12.3455553333333"
> 4> list_to_float(floaty:auto(12.3455553333333)).
> 12.3455553333333
>
>
>
>
> Le 31/12/2018 à 20:31, Dan Sommers a écrit :
> > On 12/31/18 10:37 AM, Vans S wrote:
> >
> >  > > 1> 0.0001.
> >  > 0.0001
> >  > > 2> 0.00001.
> >  > 1.0e-5
> >
> >  > Once floats get to the 4th/5th decimal place they start being
> >  > displayed with the e-x notation.  Is there a way to make them always
> >  > display "normally", for example 0.00001 in this case ...
> >
> > At some point, it's shorter and easier to read with the e-x notation.
> >
> > Consider a number like 1e-44.  The last thing I want is to have to count
> > all those zeros.  ;-)
> >
> > But you probably knew that.
> >
> >  > ... The problem is when you turn the float into a string, its also
> >  > displayed as 1.0e-5, adding a format function works yes, but gets
> >  > annoying to maintain when you need to do arithmetic on the floats.
> >  > LIke sorting by the value.
> >
> > I'm confused:  if you're doing arithmetic on the floats, why are you
> > concerned with the strings?
> >
> > If you're sorting the strings, then you'll probably either (a) have to
> > ensure a consistent format, perhaps with something like a ~24.18.0e
> > specifier, or (b) convert the strings back to floats and suffer various
> > rounding errors.
> >
> >  > Also debugging becomes annoying when you see the e-5, e-6, etc
> >  > notation everywhere and have to match it up.
> >
> > On that we agree.  :-)
> >
> >  > Is there a way to compile / add arg to the VM to not do this?
> >
> > I'm pretty new at Erlang, so I'm probably missing a lot, but how are you
> > displaying the values now if not with a format function?  (I guess
> > there's io:write, but at that point, you're awfully close to calling
> > io:fwrite anyway.)
> >
> > Are you just using the shell to do immediate calculations?  I'm sure
> > that the shell has its own default formatting, or maybe it just calls
> > io:write.
> >
> > Dan
> > _______________________________________________
> > erlang-questions mailing list
> > 
> > http://erlang.org/mailman/listinfo/erlang-questions
> >
>
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> 
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