Here is a small awkwardness with naming.
Example.
Defining the operation of the set cardinality, we put naturally
that it may return
FiniteCard n, n >= 0 :: Integer
InfiniteCard,
UnknownCard
But in this case, - as in many others, - there are several values
in result which clearly cannot be returned by the operation.
Thus, in the example, we can put
class Set where card :: a -> Integer --has a sample argument
...
and let card to return -1 for InfiniteCard, -2 for UnknownCard
- and obtain the plainer program than by introducing the new data
constructors.
To make it even better, we have to name -1, -2 with the appropriate
names and use them by names. Now, if we define
infiniteCard = -1
then the pattern matching suffers:
case card a of infiniteCard -> g infiniteCard
_ -> 2
will yield wrong thing.
Using the cpp preprocessor
#define InfiniteCard -1
would not do any good. Because cpp processes badly all the files
where (') occurs - extra improvements for (') will spoil the
plainness more than the constant naming helps it.
I decided remain with case card a of -1 -> g infiniteCard
_ -> 2
But could anybody advise any better solution?
------------------
Sergey Mechveliani
[EMAIL PROTECTED]
