On 10 Feb 2024, at 10:45, Al <frm.ml@mailgw.com> wrote:
On 2024-02-10 11:20, Pietro Cerutti wrote:Both Haskell and CHICKEN ultimately compile to obiect code. That is not important: the important thing is the abstract machine you're programming against. This is why I specified "observable" in my previous reply.
I agree. And if we step out of the monadic framework for just a bit, you'll see that there's room for an abstract machine in which purity just means "does not set! globals". This would still let the optimizer know that globals do not need to be re-checked after such a procedure is invoked, for example. I'm not sure if csc really uses the full "referentially transparent" definition (i.e. memoize-able), or just the "does not modify globals" one.On a practical level, I would be sad if vector-ref, for example, was "impure", and thus compiling a vector-ref invalidated all previously-checked globals for the current scope. Likewise, I would prefer to declare a procedure using vector-ref as pure, to let csc know that it does not modify globals (or the filesystem etc).
I don't see why vector-ref would be any less pure than, say, a let binding. Or do you mean vector-set! ?
If the latter, well.. wouldn't your reasoning prevent you from using vector-set! on a global variable?
-- Pietro Cerutti I've pledged to give 10% of income to effective charities and invite you to join me. https://givingwhatwecan.org
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