Re: [Haskell-beginners] GHCi bug?

I know the code isn't correct. My point is that the compiler didn't complain when the code was loaded, and the interpreter died when it was executed. That shouldn't happen. * -- Russ* *** * ** On Mon, Nov 15, 2010 at 9:10 PM, Antoine Latter wrote:

On Mon, Nov 15, 2010 at 9:59 PM, Russ Abbott wrote:

...

This looks like a GHCi bug. Load a file with these two lines into GHCi

data Test = Test instance Show Test where -- No body to the instance statement

A Show instance without a body isn't valid. Perhaps you wanted:

...

data Test = Test deriving Show

If you take a look at the source for the Show class:

http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/src/GHC-Show....

you can see that the function 'show' has a default implmentation of 'show' in terms of 'showsPrec', whicle 'showsPrec' has a default implementation in terms of 'show', so you end up with an infinite loop.

The idea is that you can pick which one to implement - but you do need to pick :-)

Antoine