[Haskell-cafe] Re: Is 78 characters still a good option? Was: breaking too long lines

[Christian Maeder]

Richard O'Keefe wrote:
> 
> On 25 Apr 2009, at 8:59 pm, Miguel Mitrofanov wrote:
> 
>> Something like
>>
>> newtype MyCoolMonad = MyCoolMonad (FirstTransformer (SecondTransformer
>> (ThirdTransformer Whatever))) deriving (Functor, Monad, FirstClass,
>> SecondClass, ThirdClass, SomeOtherClass)
[...]
> For what it's worth, my personal Haskell style lines up
> 
> data T
>    = C1 ...
>    | ...
>    | Cn ...
>    deriving (...)

This has the clear advantage that indentation does not depend on the
length of the type name as in the quite typical layout of Xiao-Yong Jin:
http://www.haskell.org/pipermail/haskell-cafe/2009-April/060541.html

> so I'd have this as
> 
> newtype MyCoolMonad
>       = MyCoolMonad (FirstTransformer (SecondTransformer
> (ThirdTransformer Whatever)))
>       deriving (Functor, Monad, FirstClass, SecondClass, ThirdClass,
> SomeOtherClass)
> 
> where the longest line is 86 columns.

(which is still too long as my reply-wrap proofs.)
[...]

However, indenting by 3 or 6 characters depending on "data" or "newtype"
 is also a bit arbitrary. Consider:

newtype MyCoolMonad =
    MyCoolMonad
      (FirstTransformer
        (SecondTransformer (ThirdTransformer Whatever)))
  deriving
  ( Functor, Monad, FirstClass, SecondClass, ThirdClass
  , SomeOtherClass)

Either all alternatives fit on one line or they go on separate lines
each. The  same should apply to all components of one alternative.
Additionally, as above, a long type-application may need to be broken
over several lines. (Breaking before "=" and having "=" above "|" looks
also nice.)

Pretty-printing a comma-separated list (following deriving) is an extra
subject with a couple of variations:

Putting commas in the front, better indicates the continuation, but the
extra space following the open bracket "(" looks a bit odd. (Surely one
could also leave a space before the closing bracket, although I wouldn't
like spaces around all brackets.)

The alternative:
   (Functor, Monad, FirstClass, SecondClass, ThirdClass,
    SomeOtherClass)

has the disadvantage, that the second line is only indented by one
character (relative to the previous one), but intending further (+1 or
+3 or even one less) is an alternative.

(I'm no friend of putting the closing bracket on a separate line in the
same column as the opening one. Too easily such indentations are messed
up.)

Cheers Christian