[Haskell-cafe] APIs

[Jan-Willem Maessen]

On May 24, 2005, at 5:28 PM, John Meacham wrote:

> [various ways of capturing options passed to functions discussed...]
>
> I think it is easier just to declare it as Enum..
>
> data ParentsFlag = DontCreateParents | CreateParents
>         deriving(Enum)
>
> now (toEnum . fromEnum) will convert between ParentsFlag and Bool.

Ah, but imagine I don't have the module source handy.  Which 
corresponds to True and which to False?

Mostly, I stay away from enumerations whose order matters, making a 
particular exception for Bool and Ord.

If the names are (as above) DontDoSomething | DoSomething, using a 
newtype plus a boolean conveys the same sense without the 
forgetfulness:

newtype CreateParents = CreateParents Bool

createDirectory (CreateParents False)

-Jan-Willem Maessen