Haskell, range down without a step

Question

Why Haskell doesn't work range down without step

[7..1] => [] 

but only works with this

 [7,6..1] => [7,6,5,4,3,2,1] 

Answer 1

3.10. Arithmetic sequences

[...] Arithmetic sequences satisfy these identities:

• [...]
• [e1..e3] = enumFromTo e1 e3
• [...]

6.3.4 Class Enum

For Int and Integer types, enumeration functions have the following meanings:

• [...]
• The sequence enumFromTo e1 e3 is a list of [e1, e1 + 1, e1 + 2, ... e3]. The list is empty if e1> e3.
• [...]

From the Haskell 2010 Language Report .

Answer 2

Haskell has no way of knowing that you want to take step -1 until you give it a hint.

There may be situations when you need a range [x..y] where y < x and where you expect the range to be empty. This would create subtle errors if Haskell simply went down in these cases.

Answer 3

Without specifying a step, haskell assumes it is +1 and returns an empty list if it is not applicable to the given parameters.

Any addition other than +1 should be explicitly suggested; not only positive integrals> 1.