Re: Object-relational impedence

On Mar 10, 5:30 am, "Yagotta B. Kidding" <y..._at_mymail.com> wrote:
> Marshall <marshall.spi..._at_gmail.com> wrote
> > On Mar 9, 7:25 pm, "Yagotta B. Kidding" <y..._at_mymail.com> wrote:
>
> >> Superficially, you can perform the translation, but the assignment
> >> required to imitate the projection makes any such language not
> >> referentially transparent. You may consider the non-transparency a
> >> non- issue of course.
>
> > Um, how so? I'm not sure I see what you mean.
>
> "A language that supports the concept that ``equals can be substituted
> for equals'' in an expresssion without changing the value of the
> expression is said to be referentially transparent. Referential
> transparency is violated when we include set! in our computer language.
> This makes it tricky to determine when we can simplify expressions by
> substituting equivalent expressions. Consequently, reasoning about
> programs that use assignment becomes drastically more difficult."

Dude? I'm a language junkie with an interest in FP. It wasn't the term "referential transparency" I was having trouble with. :-)

Rather, I don't see where the assignment comes in. Particularly in discussing SQL, which, strictly speaking, lacks assignment. (Although it does have other imperative operators, yes.) And Mr. Perryman's example was written in a single-assignment, mathematical style.

> http://mitpress.mit.edu/sicp/full-text/sicp/book/node54.html

Ah, SICP. Did you know that David Cressey's name appears in it? Apparently he was at ground zero in the early days of garbage collection, and coined a term that is still used. I told that story when my languages discussion group had Mr. Abelson for lunch.

Marshall

PS. Name dropping alert!!! I try to resist, but I am weak. Received on Mon Mar 10 2008 - 16:38:38 CET