[plt-scheme] Re: analogies

On Oct 18, 2005, at 5:36 PM, karczma at info.unicaen.fr wrote:

> Matthias Felleisen writes:
>> J. Karczmarczuk:
>
>>> In which sense BSL is more than Scheme?
>
>> BSL supports define-struct; R5RS doesn't.
>
> Oh. I always used the language which included MrEd. I thought that it
> was based on R5RS...
> It seems that this "being more than Scheme" applies to other PLT 
> languages
> as well...

Yes, __all__ PLT languages supported in DrScheme are "more" than R5RS 
in this sense; some are __far__ more (Pretty Big, Module).

R5RS is the specification of a language family:
  - implementations may refine the behavior
  - implementations are allowed to be safe (the standard isn't)
  - implementations usually extend the core language

It is for this reason that it is difficult to port Scheme programs from 
one implementation to an other.

In comparison, SML is indeed a standard and an SML implementation 
always implements the semantics of SML. It may extend the core language 
via libraries and additional forms but these extensions are (must be) 
conservative.

Example: SML/NJ (ie, the SML system that originated in New Jersey) 
provides call/cc at the core level and higher-order functors at the 
module level.

Haskell's situation is similar but there are far fewer implementations.

-- Matthias