[GHC] #9548: Numerical type system problem

[GHC]

#9548: Numerical type system problem
-------------------------------------+-------------------------------------
       Reporter:  vxanica            |                   Owner:
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  libraries/base     |                 Version:  7.8.3
       Keywords:  Number             |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
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 Originally, in haskell 98 the factorial function
 {{{#!hs
 f 0 = 1
 f n = n * f (n - 1)
 }}}
 has type Num a => a -> a, while after ghc 7.4 it requires Eq type class.
 I suggest that Num type class should be redefined as
 {{{#!hs
 class Eq a => Num a where
    ...
 }}}
 Since all the numbers are equality checkable. we can be more aggressive to
 have Order super class for numbers even complex numbers are not well
 ordered.
 I suppose that this is like the historical problem like Applicative should
 be the super class of Monad.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9548>
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