Enum, Bounded, and Arithmetic Sequences

[Ferenc Wagner]

Johannes Waldmann <joe@informatik.uni-leipzig.de> writes:

>>  x :: Foo <- [ .. ] 
>
> A related point: the Haskell definition states that
For any type that is an instance of class Bounded as well as
Enum, the following should hold:
>
>> enumFrom and enumFromThen should be defined with an implicit bound, thus:
>>   enumFrom     x   = enumFromTo     x maxBound

> I think this should be enforced -
> the *only* method in Enum should be `enumFromTo'.
>
> If one writes [ x .. ], then the compiler expands this to 
> `enumFromTo x  maxBound', and therefore adds a `Bounded' constraint.
> Likewise, [ .. y ] expands to `enumFromTo minBound y',

No, "half" infinite list like [1..] are useful.

> and [ .. ] to  `enumFromTo minBound maxBound' .

This I would not mind, I can not think of another reasonable
translation.  But why not define

elements :: (Enum a, Bounded a) => [a]
elements = [minBound .. maxBound]

instead?

> PS: and enumFromThenTo should just be removed, alongside n+k patterns :-)

Or preferably the Floating and Double Enum instances...
                                                            Feri.