Building large datastrucutures (graphs) with FC

[Cypher1]

Hi all,

I'm having some trouble building structures inside FC.
I have a Graph type with some methods (e.g. addNode(label), addEdge(from, to)) and I'm trying to build structures with a set of properties (like being forests of n-trees).

In fast check arbitrary code, this isn't 'hard' exactly, but the output is not particularly readable, as there's a lot of chaining and mapping.

I'd love to do something more monadic, unwrapping as I go, but the nesting gets very deep.

Am I missing some APIs for this in fastcheck?

Something like
https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBAMwMaKhEcDkCCGBnGAWiQAsBTJAa0wG4AoOpAG3zzgHEocwS4BvOnDgA7CABMyeAFxwCUYMIDmAbQC6cALxw19IWTGLJM5XIWKANLJjylqtZu2r6guEgjC5AVyQxoACigyHDF3JgBPOGAxGVMlS0Dg0IjhHBAyGOszAEp+AF8GIRAcSjIAOXEyPyiMm0UcgSEhGBJgPAA6UQl2sE88EiqxLN04fMLisgBRA0qENBAASWirWstfRZrs-hcmlvb9Q27e-uVZ9EXViEXVIZd8-LoYMLAyOAB5MBhgdzYtBrgQBTlLoAfhkwk8IAARmQoMMigAPIGSUEiCHQ2EuAHCKYHFHgqEwuE4eE45FgtGEuj3BCeYQ+L7COCKLg8AYbOIiVLpZZmSwQD4M6RvAXfBx8XL1FyBGCeKCMxBINpuDwwHDCGADLIuNpFMADTQAPhEZAA7hwWf0opYUmkslqhEqSDgFH5mYaFW1acAAI6eMgAQSgXDCfm2Htiij8WXMYb4WIAMmQlM0ZPzPt8dYCKnhLAjE8mSKmRR4dcSkXgJWHS3qbZJ3X9Gpy0u1dX5a+7maWSki21y7cNG9LZYzmQORnaq6RncJXVB3chPcIfX7A8HQ42hAuvb6A0GcCGw42FwoYGRDFA-HGFFIAAy54lSTudSRtJhJxTNOCEOAARgllivYR8w-Qs4AAJnveFgJTcD-0PRo+H+BRoNAtNBUzbFphzf5iRQot0xLBFSWwtxwBwLhfCgGQ-BwSxIRyDQjRwZQb3UDQtEhFj1AAMm4uBmJ-NiOOUQT4KESsN0aas-H2OtGK2STG1kltuBk6YOygLtJmmWcOmzZRZK41RLCffTDME64bkUxohzlJkMWsiUbnuZUCCZBwFzwVIwDfWduH6TAWkwSxAuAYK8n7RhvggN9XwgSM6hoIA

Thanks in advance :)

[Cypher1]

I had another go

https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBAMwMaKhEcDkCCGBnGAWiQAsBTJAa0wG4AoOpAG3zzgHEocwS4BvOnDgA7CABMyeAFxwCUYMIDmAbQC6cALxw19IWTGLJM5XIWKANLJjylqtZu2r6guEgjC5AVyQxoACigyHDF3JgBPOGAxGVMlS0Dg0IjhHBAyGOszAEp+AF8GIRAcSjIAOXEyPyiMm0UcgSEhGBJgPAA6UQl2sE88EiqxLN04fMLisgBRA0qENBAASWirWstfRZrs-hcmlvb9Q27e-uVZ9EXViEXVIZd8-LoYMLAyOAB5MBhgdzYtBrgQBTlLoAfhkwk8IAARmQoMMigAPIGSUEiCHQ2EuAHCKYHFHgqEwuE4eE45FgtGEuj3BCeYQ+L7COCKLg8AYbOIiVLpZZmSwQD4M6RvAXfBx8XL1FxuDzwHBQSHAaxysKkhx+ZkyTjcEg5DQAPkQSDatOAAEdPGQAIJQLhhPzbQ1tBQwMiGKB+PhYqQABksCKkzI6FXaTDISmacEIcAAjBLLJ6FAAZMOKZoyABMfuJyfDJAzozgNyE0oIcDlCqVUBV0x+cHVUE1LJ1mgNyGNwjNFuttvtjTL8sVXCrpPrWXMDr4-yTKbTcH5n2+bSxpLwWfhOdTebnIo8S+JK8sbnAcpwvgbdZwlkhuoNOGU3vUGi0kPv6gAZG+y8po4-n9-VLcNwuIEMCeFAjJtoEbhQGIHoOtUQhtiWMA4MIMADGODopGkMhId8KFoX42FkJhfadEYjomuaVo2jgdptrEih+GO-BYhus7zoKS6AsGa7sVunGLgiSJ4BKgF7mAfgelEljEbJwYSi2Wx9qG8DMg4whkAA7hwTYDLJXJFo0CDQHWqkiBUc4IBZXSSn2QiBkUJRIkRFRZA6BZCCBYGMsywxiUIbSkDgCj1i2DrloOyorqOEl+PskhKX8fYmVAZlkPACWRIyCV4HZ9kOVAe4lCOCWvpYZU-kZfaeY03ngUyGI1e5Qg3PcyFMg4DGpGAob1tqfiYC0mCWENwAjXkWQ3CWEChm0TAQExdQ0EAA

I think there's a repeated pattern of performing some side effecting code with an arbitrary generated from a previous value.

It would be really helpful to have something like

arbitrary1
    .with((value1) => makeSomeArbitrary2FromValue1))
    .map([value1, value2]) => {
          ... procedural code ...
    });

And maybe

arbitrary1
    .then((value1) => { some procedural code })
    .map(updatedValue1) => {
          ... imperative code ...
    });

I think that then (or some other name) represents that I want it to be side effecting, but still work for arbitraries.
Maybe returning the updated value1 is acceptable, but ideally I don't want to have to.

[dubzzz]

Hello,

In the case of recursive structure, I'd go for fc.letrec. It will let you define recursive structures in an easier way.
Here is a pointer to the page describing it: https://fast-check.dev/docs/core-blocks/arbitraries/combiners/recursive-structure/#letrec

Otherwise, you can try fc.memo, but it's less recommended.

Or chain (as you already did) and in last resort fc.gen (last resort for fc.gen as it tends to provide bad shrinking, no replay...).

[dubzzz]

@Cypher1 did it solve your issue or help into solving it? If not, please let me know I can try to further investigate this precise case.