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<greghendershott>
dzoe: You're trying to set! the thing in the same module it's defined, and, it fails silently?
<greghendershott>
(As you know in general you can't set! something outside the module that provides it. But that gives you a clear error like "set!: cannot mutate module-required identifier".)
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<greghendershott>
A plain old contract still lets you set! within the same module. e.g. (define/contract v number? 42) and (set! v 43) is fine. (And (set! v "foo") gives you contract failure.)
<greghendershott>
I wonder if srcdoc is moving you define into a submodule then providing it.
<greghendershott>
Anyway, my lazy/"practical" answer is don't use set!. Instead use e.g. (define current-v (make-parameter 42)) and then I bet (current-v 43) will work fine with srcdoc?
<greghendershott>
It might be that srcdoc ought to be changed to accomodate set!, or it might be the design makes it hard. idk.
<greghendershott>
I think the reality is not a huge number of people use srcdoc (but I have, and like it!), and of those, people are probably being "Rackety" and using parameters or boxes or whatever to mutate.
<greghendershott>
So that small % of a % might be why "nobody" except you has noticed this? idk
<greghendershott>
Or hopefully someone smarter will come along with a better answer for you than mine.
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<greghendershott>
"I wonder if srcdoc is moving you define into a submodule then providing it." No, these are just provide sub-forms.
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<greghendershott>
Without knowing more, all I can figure is you're hitting the basic thing, that anything a modules `provide`s can't be mutated outside the module.
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<dzoe>
greghendershott: exactly
<dzoe>
And btw, I just export a different symbol now and hide the mutation strictly inside the module.
<dzoe>
What made me flummoxed was the fact that it "silently fails" if I set! the contract-exported identifier within the module.
<dzoe>
(As seen from outside of the module)
<dzoe>
I switched to parameters for identifiers with atomic values for other reasons as well, but this one is actually a generated function for which I wanted a contract.
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<liangchao>
Hi
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<greghendershott>
dzoe: It's not unusual to have parameters whose value is a function. `current-eval` and `current-print` are just a couple examples. Also parameter/c is a thing.
<greghendershott>
Admittedly `(f x y z)` is more convenient than `((current-f) x y z)` but if you do the latter a lot you can wrap that in some call-the-current-f function maybe you even name it `f`
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<jcowan>
What I want to know is, does anyone know any applications of parameters that goes beyond just storing them in global variables?
<dzoe>
greghendershott: good example, thanks - I have just started writing some serious web application in Racket so these are basically insweeped corners for me
<dzoe>
(Been writing batch and GUI applications in Racket for years)
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<greghendershott>
dzoe: btw I've found it handy to have a `config.rkt` with parameters for various app things (ports, db connections, etc.) and the parameter default value comes from `getenv`.
<greghendershott>
That might be overkill for simple web apps, or not exactly how you'd want it to work, but just FYI an idea
<greghendershott>
Oh the `secret?` bit is just a fence to help scrub certain things from getting into log files.
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<samth>
jcowan: are you asking "why are all parameters defined at the top level of some module"?
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<dzoe>
greghendershott: I was thinking about similar approach for the configuration, my struggle with srcdoc was mainly for the stuff generated by dispatch-rules and similar (recursive syntax macro menu tree builder is the second case)
<dzoe>
The dispatch function gets generated relatively lately after all modules have already been initialized - so basically it is just a single mutation during the whole program run. More like "lazy" initialization.
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<jcowan>
samth: Parameters are first-class objects. You can store them in data structures or local variables return them from functions, as opposed to binding them only to top-level variables. I am wondering if anyone exploits this flexibility.