[GHC] #15031: [1,1..0] /= [1,1..2]

[GHC]

#15031: [1,1..0] /= [1,1..2]
-------------------------------------+-------------------------------------
        Reporter:  sgraf             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  libraries/base    |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by sgraf):

 Ok, found it in section 6.3.4 of the Haskell2010 spec:
 https://www.haskell.org/onlinereport/haskell2010/haskellch6.html#dx13-131001

 > The sequence enumFromThenTo e1 e2 e3 is the list [e1,e1 + i,e1 +
 2i,…e3], where the increment, i, is e2 − e1. If the increment is positive
 or zero, the list terminates when the next element would be greater than
 e3; the list is empty if e1  >  e3. If the increment is negative, the list
 terminates when the next element would be less than e3; the list is empty
 if e1  <  e3.

 Since the increment is in fact 0 and e3=0 < e1=1, this conforms to the
 standard. What an unfortunate assymetry.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15031#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler