Re: Object-relational impedence

From: Marshall <>
Date: Mon, 10 Mar 2008 08:38:38 -0700 (PDT)
Message-ID: <>

On Mar 10, 5:30 am, "Yagotta B. Kidding" <> wrote:
> Marshall <> wrote
> > On Mar 9, 7:25 pm, "Yagotta B. Kidding" <> 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.


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.


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

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