• bearophile (4/5) Jan 05 2010 Bye,
• Andrei Alexandrescu (3/10) Jan 05 2010 That means no static checking of ordered vs. unordered types.

bearophile <bearophileHUGS lycos.com> writes:

From:
http://parasail-programming-language.blogspot.com/2009/10/using-in-parasail-to-implement-etc.html

ParaSail skirts this issue by requiring the user to define only one operator,
"=?", which returns a value from the enumeration Less, Equal, Greater,
Unordered.  The comparison and equality operators are defined in terms of "=?"
[...] "Unordered" is used for types with only a partial ordering (or no
ordering at all).  "Ordered" is defined as the subtype containing only the
values "Equal," "Less," and "Greater."  The typical generic "Sort" operation
would expect a "=?" operator whose result is guaranteed (via a postcondition)
to be within the "Ordered" subtype. The "=?" operator can be used explicitly if
desired, which is often convenient when searching a binary tree:<

Bye,
bearophile

Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:

bearophile wrote:
 From:
 http://parasail-programming-language.blogspot.com/2009/10/using-in-parasail-to-implement-etc.html
 
 ParaSail skirts this issue by requiring the user to define only one operator,
"=?", which returns a value from the enumeration Less, Equal, Greater,
Unordered.  The comparison and equality operators are defined in terms of "=?"
[...] "Unordered" is used for types with only a partial ordering (or no
ordering at all).  "Ordered" is defined as the subtype containing only the
values "Equal," "Less," and "Greater."  The typical generic "Sort" operation
would expect a "=?" operator whose result is guaranteed (via a postcondition)
to be within the "Ordered" subtype. The "=?" operator can be used explicitly if
desired, which is often convenient when searching a binary tree:<

 
 Bye,
 bearophile

That means no static checking of ordered vs. unordered types.

Andrei