Enum class

[Malcolm Wallace]

I just thought I should add the results for hbc and nhc98 to this
enumeration of woes, to further illustrate the difficulties.

> i :: Int
> i = 0x7fffffff
> 
> i_plus_1 = i+1
>   -- ghc :  -2147483648
>   -- hugs:  -2147483648
    -- nhc98: -2147483648
    -- hbc:   -2147483648

> i_succ = succ i
>   -- ghc : *** Exception: Prelude.Enum.succ{Int}: tried to take `succ' of maxBound
>   -- hugs:  -2147483648
    -- nhc98: -2147483648
    -- hbc:   -2147483648

> j :: Int
> j = 0x80000000
>   -- ghc :  -2147483648
>   -- hugs:  Program error: {primIntegerToInt 2147483648}
    -- nhc98: -2147483648 (+ warning: decimal constant is so large that it is unsigned)
    -- hbc:   -2147483648

> k :: Int
> k = 0x100000000
>   -- ghc :  0
>   -- hugs:  Program error: {primIntegerToInt 4294967296}
    -- nhc98: 0
    -- hbc:   0

> i':: Integer
> i'= 0x7fffffff
> i_plus_1' = i+1
>   -- ghc :  2147483648
>   -- hugs:  2147483648
    -- nhc98: 2147483648
    -- hbc:   2147483648

> i_succ' = succ i'
>   -- ghc :  2147483648
>   -- hugs:  -2147483648
    -- nhc98: -2147483648
    -- hbc:   -2147483648

> I think Hugs is wrong.  Integer shouldn't wrap.

(Actually, ghc is `wrong': hbc, hugs and nhc98 match the Report's
specification here:   succ = toEnum . (+1) . fromEnum
This is confirmed by the description of the semantics in section 3.10.)

> succ 1.45
>     -- hugs:  2.0
>     -- ghci:  2.45
      -- nhc98: 2.0000000000000000
      -- hbc:   2.0

> succ 1.99
>     -- hugs:  2.0
>     -- ghci:  2.99
      -- nhc98: 2.0000000000000000
      -- hbc:   2.0

> succ 1.99999
>     -- hugs:  2.0
>     -- ghci:  2.99999
      -- nhc98: 2.0000000000000000
      -- hbc:   2.0

> succ (-0.2)
>     -- hugs:  1.0
>     -- ghci:  0.8
      -- nhc98: 1.0000000000000000
      -- hbc:   1.0

> succ (-0.99999)
>     -- hugs:  1.0
>     -- ghci:  9.99999999995449e-6
      -- nhc98: 1.0000000000000000
      -- hbc:   1.0

> succ (-1.1)
>     -- hugs:  0.0
>     -- ghci:  -0.10000000000000009
      -- nhc98: 0.0000000000000000
      -- hbc:   0.0

Ghc does not follow the Report here either.

> [1.0..2.5]
>     -- hugs:  [1.0,2.0,3.0]
>     -- ghci:  [1.0,2.0,3.0]
      -- nhc98: [1.0000000000000000,2.0000000000000000]
      -- hbc:   [1.0,2.0,3.0]

> [1.1..2.5]
>     -- hugs:  [1.1,2.1]
>     -- ghci:  [1.1,2.1]
      -- nhc98: [1.0000000000000000,2.0000000000000000]
      -- hbc:   [1.1,2.1]

> [1.1..3.0]
>     -- hugs:  [1.1,2.1,3.1]
>     -- ghci:  [1.1,2.1,3.1]
      -- nhc98: [1.0000000000000000,2.0000000000000000,3.0000000000000000]
      -- hbc:   [1.1,2.1,3.1]

nhc98 is wrong for all the Double arithmetic sequences.

Regards,
    Malcolm