[Haskell-cafe] Re: Channel9 Interview: What makes imperative programming so difficult

mgsloan mgsloan at gmail.com
Wed Jan 31 18:35:29 EST 2007

Reminds me of an HWN quote from a few weeks back.

Jan 9, 2007 HWN
"*Paul Johnson*: Mutable state is actually another form of manual memory
management: every time you over-write a value you are making a decision that
the old value is now garbage, regardless of what other part of the program
might have been using it."

On 1/31/07, Doaitse Swierstra <doaitse at cs.uu.nl> wrote:
> If you ask an "ordinary" programmer what is the effect of an
> assignment like:
> x := <expr>
> you will get an answer along the lines: the <expr> is evaluated and
> the result is stored in a box named "x".
> If you ask him/her whether something else has happened the answer
> will usually be "no"; and this is the wrong answer, since one tends
> to overlook the fact that one has, by mentioning the variable "x",
> also indicated that the old value of "x" is no longer needed. As such
> imperative programming is "functional programming with explicit
> garbage collection".
> This may have been a necessity in the old days, when memory was
> scarce and machines slow (in my first course on numeric algorithms we
> were taught to declare the variables x, y, z, n, m, i, and j, and the
> array a, and to solve our problems with those only; points would be
> deducted for making use of more variables, or not reusing whenever
> possible!). Nowadays I think everyone agrees that automatic garbage
> collection is a good thing; think about the amount of wasted
> programmer years of people figuring out where they have space leak,
> etc., and users of programs getting a disappointing feeling about
> computer science as a whole since apparently we keep delivering
> programs that stop to work at unpredictable moments.
> So, one might wonder whether assignments are always bad, bringing us
> back to the OO discussion. Of course if we have the following
> expression:
>   digest.chew.eat.serve.cook.chop.pluck.kill $ chicken
> we all have a definite feeling that after applying the functions, the
> original object is no longer available, and the FP view does not feel
> entirely natural.
>   Doaitse Swierstra
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