Chris Smith wrote:
> David Hopwood <[EMAIL PROTECTED]> wrote:
>
>>This is true, but note that postconditions also need to be efficient
>>if we are going to execute them.
>
> If checked by execution, yes. In which case, I am trying to get my head
> around how it's any more true to say that functional languages are
> compilable postconditions than to say the same of imperative languages.
A postcondition must, by definition [*], be a (pure) assertion about the
values that relevant variables will take after the execution of a subprogram.
If a subprogram is intended to have side effects, then its postcondition
can describe the results of the side effects, but must not reexecute them.
[*] E.g. see
<http://www.spatial.maine.edu/~worboys/processes/hoare%20axiomatic.pdf>,
although the term "postcondition" was introduced later than this paper.
--
David Hopwood <[EMAIL PROTECTED]>
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