Thanks Eamonn for sharing! The article and its references led to very interesting reading.
In principle I don't see an issue with adding such a function, but I believe we need to survey other languages and see what they are calling it and which edge cases they consider too. Using the code above may be ok at the end, it is under Creative Commons, but we need to survey around before. :) On Thu, May 20, 2021 at 12:21 AM Eamonn O'Brien <[email protected]> wrote: > Hi All, > > My first post here, so hello all and thanks for all the great work on > Elixir so far! > > This is a relatively simple proposal. Many of the Float functions already > take precisions and, floating point arithmetic being what it is a > comparison function that takes some sort of epsilon value is almost > required for a lot of floating point work. > > As https://floating-point-gui.de/errors/comparison/ outlines writing such > a function is both tricky and error prone so adding an implementation of > that function to the core library makes sense. > > I would propose a spec something like: > > @spec nearly_equal?(float, float, precision) :: bool > > Using an epsilon value instead of a precision might make more sense in > some contexts but since the rest of the functions in Float use a precision > value that is probably more consistent. > > Arguments for: > > The documentation for Float already links to the above article discussing > why such a function might be needed. Adding an implementation probably > makes sense. > > It is a sufficiently widely used function that a default implementation in > the standard library is not going to be clutter. > > It is a tricky function to get right and providing a default > implementation would be beneficial. > > Having it available might make devs more likely to use it instead of > comparison or pattern matching floats. > > Arguments against: > > The function can already be written using the tools provided in the core > language. Implementation of such a function is not necessary and arguably > is something domain specific that should be written per project. > > It doesn't behave very well with pattern matching. This could of course be > rectified by making it usable as a function clause ala: > > def float_stuff(x, y) when nearly_equal?(x, y, 5), do ... > > There may be a copyright issue with just writing a version of the code > linked. > > Alternatives: > > Using the same spec but calling the function equal? and defaulting > precision to 15 might make more sense. > > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/23f8e3a6-0aa6-426c-bb67-497a6bd7bf66n%40googlegroups.com > <https://groups.google.com/d/msgid/elixir-lang-core/23f8e3a6-0aa6-426c-bb67-497a6bd7bf66n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4%2Bt6Qj6HnR9%2BvmGjAnLFwe4hjsYJgdwXWYb9njUirWggg%40mail.gmail.com.
