#2076: rational infinities don't compare correctly to each other ---------------------------------+------------------------------------------ Reporter: uhollerbach | Owner: jeffrey Type: bug | Status: new Priority: normal | Milestone: _|_ Component: libraries/base | Version: 6.8.2 Keywords: | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------

Comment(by jeffrey): In libraries/base/GHC/Real.lhs, I added {{{ instance (Integral a) => Ord (Ratio a) where {-# SPECIALIZE instance Ord Rational #-} + (x:%0) <= (x':%0 ) = x < 0 || 0 < x' + (x:%0) <= (_ :%_ ) = x < 0 + (_:%_) <= (x':%0 ) = 0 < x' (x:%y) <= (x':%y') = x * y' <= x' * y + (x:%0) < (x':%0 ) = x < 0 && 0 < x' + (x:%0) < (_ :%_ ) = x < 0 + (_:%_) < (x':%0 ) = 0 < x' (x:%y) < (x':%y') = x * y' < x' * y }}} which passes my testsuite for this bug. However, I also tested the equivalence of same-sign infinities (which I assumed to be a desired property when I wrote the code) and found that it wasn't working; for example {{{ Prelude GHC.Real> (2:%0) == (1:%0) False }}} When I also found that, for example, {{{ Prelude GHC.Real> (2:%4) == (1:%2) False }}} I figured that (:%) wasn't intended to equate different forms of actually- equal ratios. So I figured my proposed bug fix would just introduce another bug, since it, for example, yields {{{ Prelude GHC.Real> (2:%0) < (1:%0) -- should be False False Prelude GHC.Real> (2:%0) <= (1:%0) True }}} which contradicts the non-equality observed above. But then I tried {{{ Prelude GHC.Real> compare (2:%4) (1:%2) LT Prelude GHC.Real> (2:%4) < (1:%2) False }}} which doesn't make sense(?), and figured I'm probably missing the bigger picture here. Thoughts? -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2076#comment:6> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler _______________________________________________ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs