[Haskell-cafe] Re: Perl-style numeric type

[Derek Elkins]

On Wed, 2007-06-20 at 11:36 -0400, Brent Yorgey wrote:
> On 6/19/07, Brent Yorgey <byorgey at gmail.com> wrote:
>         I've started developing a library to support a "Perl-style"
>         numeric type that "does the right thing" without having to
>         worry too much about types...
> 
> So, I just completed my implementation and decided to test it out by
> converting a simple program I wrote the other day (which exhibited
> lots of fromIntegers and such) to use my generic number type.  When I
> was done converting, the code looked much simpler, which was nice.  It
> type-checked and compiled just fine.  And... didn't work.  After a
> number of minutes of fiddling around, I finally realized that
> something which I "knew" was an integer was actually being represented
> as a Double internally due to some operator I had used previously,
> which was causing the isSquare function to always return False
> (equality of floating-point numbers and all that =P ).  Adding a call
> to "round" fixed it, BUT I sheepishly realized that yes, I had just
> spent five minutes tracking down a bug that the type checker would
> have found for me had I not worked so hard to do stuff behind its
> back. 
> 
> Consider me chastened!  *goes off to contribute to that wiki page that
> Henning started...*

Well... that was entertaining.