[Haskell-cafe] HANSEI in Haskell?

Chung-chieh Shan ccshan at cs.rutgers.edu
Tue Mar 1 01:02:52 CET 2011

Daryoush Mehrtash <dmehrtash at gmail.com> wrote in article <AANLkTim0LTOviud2fyzU7NAsraQMuCKa=QYfroXn87kx at mail.gmail.com> in gmane.comp.lang.haskell.cafe:
> I see the problem now.  But I am confused as to why there are no Bool class
> (like Num, Fractional...) in Haskell.   If I had such a class then the
> problem is solved, (by making the "pm a" an instance of it) right?  Or are
> there still more issues that I am not seeing?

Sorry, I gave a bad example.  Here are two more general symptoms of
direct style: being able to write something like

    f (if flip 0.3 then LT else EQ)

where f is an existing function that takes an Ordering argument, and
even being able to write something like

    and (map flip [0.3, 0.5])

where and :: [Bool] -> Bool
      map :: (a -> b) -> [a] -> [b]
are existing functions.

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