Skipping the Hastings computation for symmetric proposals

[luiarthur]

This is a do-over of #45 for #41 which adds a method is_symmmetric_proposal whose behavior can be extended by users.

[devmotion]

I think this is a better way to skip computations for symmetric proposals 👍

I added some comments and suggestions.

[devmotion]

Can you add some explanation here?

[luiarthur]

Just added some documentation there.

[devmotion]

This is not a very "nice" example - usually one would want to define the trait for a custom proposal or distribution.

[devmotion]

Maybe define a custom distribution, e.g., of normal distributions with zero mean?

[luiarthur]

Sounds good to me.

[luiarthur]

Just modified the test.

[cpfiffer]

I like it! No comments from me, though could you increment the version number to 0.5.6 before this is merged in?

[luiarthur]

The tests seem to be passing. But in the logs, I see this at the beginning (before the tests are actually run):

┌ Error: Pkg.Resolve.ResolverError("Unsatisfiable requirements detected for package MCMCChains [c7f686f2]:\n MCMCChains [c7f686f2] log:\n ├─possible versions are: [0.2.4, 0.3.0-0.3.15, 0.4.0-0.4.1, 1.0.0-1.0.2, 2.0.0, 3.0.0-3.0.12, 4.0.0-4.0.4, 4.1.0, 4.2.0-4.2.4, 4.3.0-4.3.1] or uninstalled\n ├─restricted to versions * by an explicit requirement, leaving only versions [0.2.4, 0.3.0-0.3.15, 0.4.0-0.4.1, 1.0.0-1.0.2, 2.0.0, 3.0.0-3.0.12, 4.0.0-4.0.4, 4.1.0, 4.2.0-4.2.4, 4.3.0-4.3.1]\n ├─restricted by compatibility requirements with Distributions [31c24e10] to versions: [4.2.4, 4.3.0-4.3.1] or uninstalled, leaving only versions: [4.2.4, 4.3.0-4.3.1]\n │ └─Distributions [31c24e10] log:\n │ ├─possible versions are: [0.16.0-0.16.4, 0.17.0, 0.18.0, 0.19.1-0.19.2, 0.20.0, 0.21.0-0.21.3, 0.21.5-0.21.12, 0.22.0-0.22.6, 0.23.0-0.23.12, 0.24.0-0.24.6] or uninstalled\n │ ├─restricted to versions 0.20-0.24 by AdvancedMH [5b7e9947], leaving only versions [0.20.0, 0.21.0-0.21.3, 0.21.5-0.21.12, 0.22.0-0.22.6, 0.23.0-0.23.12, 0.24.0-0.24.6]\n │ │ └─AdvancedMH [5b7e9947] log:\n │ │ ├─possible versions are: 0.5.6 or uninstalled\n │ │ └─AdvancedMH [5b7e9947] is fixed to version 0.5.6\n │ └─restricted to versions 0.24.6 by an explicit requirement, leaving only versions 0.24.6\n └─restricted by compatibility requirements with SpecialFunctions [276daf66] to versions: uninstalled — no versions left\n └─SpecialFunctions [276daf66] log:\n ├─possible versions are: [0.7.0-0.7.2, 0.8.0, 0.9.0, 0.10.0-0.10.3, 1.0.0, 1.1.0] or uninstalled\n └─restricted to versions 1.1.0 by an explicit requirement, leaving only versions 1.1.0", nothing)

Any thoughts?

[cpfiffer]

I think that's because of a hangup in MCMCChains (TuringLang/MCMCChains.jl#252), but it doesn't seem to have impacted the tests so I think we can ignore it.