`Illegal instruction'

[S.D.Mechveliani]

I have `about' installed  ghc-5.00  binary on Linux, i-386-inknown.
But I have  libreadline.so.4.1  instead of  libreadline.so.3.
So, I made a symbolic link from  ..so.3  to  ..so.4.1.

Then,  import Ratio
       main = putStr (shows (0.9 :: Rational) "\n")

works and                ... 0.9 :: Double ...
yields  
                   `Illegal instruction'
report at running.
Could you tell, please,  1. does this library replacement any harm?
                         2. why `Illegal instruction' ?

-----------------
Serge Mechveliani
mechvel at botik.ru