Grigory Shepelev
Question for #scheme ☯️ kings & queens 👑 ! Are there an alternative to clojure's alter-var-root https://clojuredocs.org/clojure.core/with-redefs in scheme?
Imagine I have a module `(X)` with `(define a 1) (define-public (f x) (+ x a))` and module `(Y)` that has `#:use-module (X)`. In `(Y)` want to alter a from `(X)` in a way that would also affect `f`. Example: (being in module `(Y)`): `(alter! a 2) (equal? (f 3) 5) => #t`
Andy Wingo
@shegeley @rml @cwebber most schemers are republicans, in the anti-monarchist sense :) but if the intended use case is global monkeypatching, then in guile `set!` is your tool. if `a` is exported, then just `set!` on `a`. if not, `(set! (@@ (X) a) new-val)`
Andy Wingo
@shegeley @rml @cwebber but generally for this to be possible you need to have inhibited some optimizations by opting into a different dialect. see https://www.gnu.org/software/guile//manual/html_node/Declarative-Modules.html
Andy Wingo
@rml @shegeley @cwebber @monkey1 if your mental model is still “a top-level var reference necessarily loads the current value from its storage location” you need to be compiling without optimizations, otherwise you will have unpleasant surprises
Andy Wingo
@rml @shegeley @cwebber @monkey1 the issue is entirely about language: is a define form essentially a creation of a mutable storage location along with an initial value? if so, AOT inlining of top-level definitions is impossible; the compiler cannot reason about the values of top-level / module-level definitions. guile moved away from this model with declarative modules.
blake shaw 🇵🇸
@shegeley @wingo @cwebber @monkey1 oh wait I think I misread your problem
Grigory Shepelev
yep. the problem was totally in the testing env
blake shaw 🇵🇸
@shegeley @wingo @cwebber @monkey1 so you just need to create an alias? In that case (define my-alias the-original) works fine except when dealing with syntax. In that case, you can do
(define-syntax my-alias
(identifier-syntax the-original))
Might have left something out of that bcs im writing from my phone, currently on the move, so lmk if that didn't work and ill take a look.
Grigory Shepelev
it won't update setted variable's value in all procedures of `(X)` that uses `x`. `(define (square r pi) (* r r pi))` <-- here pi will stay 3.14 when `square` will be called from `(Y)`
Grigory Shepelev
@rml @wingo @cwebber @monkey1 probably the answer given was toatally correct. set! and stuff will work in repl, but won't when launched in the testing env that I just set up.
blake shaw 🇵🇸
@shegeley @wingo @cwebber @monkey1 whats the problem with `set!` in this scenario?
Grigory Shepelev
Imagine that you have a module already written by someone that does the job you want to, but there is only one variable (example `(define pi 3.14)` ) that you want just override but otherwise would like everything to work as previously. Wouldn't like to copy-paste a one of code
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