[Haskell-cafe] The instability of Haskell libraries

[Roman Leshchinskiy]

On 24/04/2010, at 18:54, Ivan Lazar Miljenovic wrote:

> Roman Leshchinskiy <rl at cse.unsw.edu.au> writes:
> 
>> On 24/04/2010, at 18:06, Ivan Lazar Miljenovic wrote:
>>> I would think that the API is all the
>>> functions/classes/datatypes/instances/etc. exported from the library in
>>> combination with their types.
>> 
>> So the semantics of those functions doesn't matter at all?
> 
> What do you refer to by "semantics"?  Can you provide an example of when
> what you consider to be the API to change when the functions, types,
> etc. don't?

John Goerzen gave one in the very first post of this thread: the fix to old-locale which didn't change any types but apparently changed the behaviour of a function quite drastically. Another example would be a change to the Ord instances for Float and Double which would have compare raise an exception on NaNs as discussed in a different thread on this list. Another one, which is admittedly silly but demonstrates my point, would be changing the implementation of map to

map _ _ = []

In general, any significant tightening/changing of preconditions and loosening/changing of postconditions would qualify. 

Roman