null references redux + Looney Tunes

[language_fan]

Sun, 04 Oct 2009 17:39:50 -0400, Justin Johansson thusly wrote:

> Nick Sabalausky Wrote:
>> "I've also
>> been wondering if it might be a huge benefit for distinguishing between
>> strings that represent a filename vs file content vs
>> file-extention-only vs relative-path+filename, vs absolute-path-only,
>> etc. I've been really wanting a better way to handle that than just a
>> variable naming convention.)"
> 
> Bingo. I'm sure there would be a huge benefit to be able to distinguish
> string or any primitive type in such manner without having to invent a
> Filename class, AbsolutePathName class etc.

You could use a variant:

typedef Filename = char[];
typedef Path = char[];

typedef File = JustFile Filename
             | RelPath Path Filename
             | AbsPath Path Filename

> 
> This whole business about types is much to do about how to construct
> (and validate) the type from primitive information -- often given in
> lexical form.  If I pass an email-address type (even if it is really
> just a string) to an sendmail function, that function should not have to
> revalidate/reparse the string to be sure that the string data is indeed
> a (lexically) valid email address.

Something that came to my mind while reading this: typedefs could also be 
extended to support contracts just like functions.