[Haskell-cafe] Bool as type class to serve EDSLs.

[Henning Thielemann]

On Thu, 28 May 2009, Bulat Ziganshin wrote:

> i use another approach which imho is somewhat closer to interpretation
> of logical operations in dynamic languages (lua, ruby, perl):
>
> a ||| b | isDefaultValue a = b
>        | otherwise        = a
>
> a &&& b | isDefaultValue a = defaultValue
>        | otherwise        = b
>
> -- Class of types having default value:
> class    Defaults a      where defaultValue :: a
> instance Defaults ()     where defaultValue = ()
> instance Defaults Bool   where defaultValue = False
> instance Defaults [a]    where defaultValue = []


The absence of such interpretations and thus the increased type safety was 
one of the major the reasons for me to move from scripting languages to 
Haskell.