The problem: Given a big, hairy, often-changing Route custom type, and a pair of functions Route -> String and String -> Maybe Route, how can we be sure that (almost) every Route turned into a string and back into Route produces the same value that we started with? Route looks like: module Route …

I also encountered this situation (almost everyone writing this kind of Route module does!). What I do for now is to write (by hand) a routeFuzzer : Fuzzer Route being in charge of randomly generate all possible routes and then I only have one test being: fuzz routeFuzzer "Test route seria…

Maybe https://package.elm-lang.org/packages/MartinSStewart/elm-serialize/1.2.1/ can help, but I’ve never used it. @MartinS could maybe give more details.

If you want to store data in a url and the format doesn’t matter (i.e. you’re okay with domain.com/<nonsense text>) then elm-serialize could work. In this case it looks like the url needs to have user readable paths so this wouldn’t work. Edit: Codecs (generating both the encoder and decoder from a…

Thanks sebbes! I had tried to go the Fuzzer route, but not being able to automatically catch and test new variants seemed like a deal-breaker. I hadn’t considered the codec approach… keeping the encoder and decoder right next to each other should make it obvious when one’s been missed, and hopefull…

Martin’s idea about Codecs is to safely build decoder/encoder from small composable blocks. If you build a Codec only using his lib, you’ll have the GUARANTEE the decoder/encoder are in sync (except maybe only for customTypes I think, where the definitions are separate ; so you only have to be very …

[image] sebbes: Martin’s idea about Codecs is to safely build decoder/encoder from small composable blocks. If you build a Codec only using his lib, you’ll have the GUARANTEE the decoder/encoder are in sync So the idea would be to write a new codec package for symmetrically parsing and buildi…

I’d love to have this! But since I am a bit lazy, I didn’t write this lib, I wrote fuzzers by hand instead… My other dream would be a tool automagically writing those fuzzers!

[image] sebbes: except maybe only for customTypes I think, where the definitions are separate; so you only have to be very careful Ah, thanks. So, the same limitation affects elm-serialize: semaphoreCodec : S.Codec Semaphore semaphoreCodec = S.custom (\redEncoder yellowEncoder g…

About the “extraction Route type”, my idea is even a bit more general: for a given type T in a module M , have a fuzzer generating value of this type using all the functions available in M. This way you can easily check invariants about T and this “parsing issue” for routes is then a trivial sub-is…

[image] rupert: So the idea would be to write a new codec package for symmetrically parsing and building URLs? Incidentally, I did try to do just that only 2 days ago. It would certainly be possible with an API similar to elm-codec, but coming up with an API that is similar to Url.Parser see…

Extracting type metadata from Elm code?

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miniBill September 11, 2020, 6:26am 17

Indeed! The type for variant0 wasn’t general enough!

https://ellie-app.com/9WK46jQ8QHta1

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Extracting type metadata from Elm code?

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