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1 point by lacker 6138 days ago | link | parent

Wow... that is gory. :-/

It seems like the most plausible way to keep scar/scdr/sref from mutating variables outside the no-side-effects scope is to keep a table of the variables they are allowed to operate on, which is basically anything the user created with cons or table inside the no-side-effects scope. This should invalidate code like

(= a (table))

(no-side-effects (= b a) (= (b "key") "value"))

Is there any more natural way to track this than keeping a table keyed by symbol?



3 points by eds 6138 days ago | link

This is probably a horribly inefficient way to implement this... but couldn't you just copy all the variables before executing the body?

Assuming

  (= a (table 'foo 'bar))
then a line like this

  (no-side-effects (= a!foo 'baz) a)
might be converted to something roughly like this

  (let a (copy a)
    (= a!foo 'baz)
    a)
a is unchanged after evaluation because the let made a deep copy that overshadowed the global value of a.

You would still have to think about constructs like def and mac, but at least this deals with shared structure of lists and tables.

Maybe something like http://arclanguage.org/item?id=3572 ?

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