[Types-sig] A type checking system in Python

[Ka-Ping Yee]

On Wed, 21 Mar 2001, Clark C. Evans wrote:
> This was a very insightful post on the main list.  
> 
> ---------- Forwarded message ----------
> Date: Wed, 21 Mar 2001 09:15:50 GMT
> From: Huaiyu Zhu <hzhu@mars.localdomain>
> 
> 			Type checking system in Python
> 
> Classes implement a hierarchy of inheritance of attributes (variables and
> methods).  They are useful for implementation modularization.
> 
> There is another type of modularization that is similar in nature, but is
> independent of classes.  This is the hierarchy of polymorphic interfaces.

Indeed.  I think it's worthwhile for anyone who's seriously thinking
about these issues to have a look at Sather's type system:

    http://www.icsi.berkeley.edu/~sather/

In particular, see:

    http://www.icsi.berkeley.edu/~sather/Documentation/LanguageDescription/contents.html

    (sections 4 and 5)

Sather separates subtyping (= substitutability) from implementation
sharing.  It also permits supertyping, i.e. declaring something to
be a supertype of another.

(As a side note, Sather has iterators and uses the keyword "yield".)


-- ?!ng

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