remove modules for verifying laws

[davidchambers]

Closes #174

Commit message:

There is now a separate package, fantasy-laws, which serves this role.

[Avaq]

This is great! Let's wait for more opinions though.

[gabejohnson]

Why are you moving Id but removing Compose and Sum? I'm assuming it's because Id is included as an example demonstrating how one might go about implementing the specification while Compose and Sum are only provided for use in the tests.

If this is the case, I would move equality and lte into id.js and remove the dependency on sanctuary-type-classes (which incidentally isn't included in package.json).

[davidchambers]

I'm assuming it's because Id is included as an example demonstrating how one might go about implementing the specification while Compose and Sum are only provided for use in the tests.

That was my thinking, yes. We could go one step further by removing the Id implementation and linking to sanctuary-identity as soon as sanctuary-js/sanctuary-identity#3 is merged (this pull request could remain open until then).

If this is the case, I would move equality and lte into id.js and remove the dependency on sanctuary-type-classes (which incidentally isn't included in package.json).

In order for Id#fantasy-land/equals to have value-based semantics one must do one of two things:

• use Z.equals in the implementation; or
• in addition to dispatching to fantasy-land/equals, provide suitable definitions for built-in types:
  • Null#fantasy-land/equals;
  • Undefined#fantasy-land/equals;
  • Boolean#fantasy-land/equals;
  • Number#fantasy-land/equals;
  • Date#fantasy-land/equals;
  • RegExp#fantasy-land/equals;
  • String#fantasy-land/equals;
  • Array#fantasy-land/equals;
  • Arguments#fantasy-land/equals;
  • Error#fantasy-land/equals;
  • Object#fantasy-land/equals; and
  • Function#fantasy-land/equals.

The file will better serve its pedagogical role if Z.equals is used in the implementation of Id#fantasy-land/equals, as this is the approach we would like ADT authors to adopt. Better yet would be to link to a complete working implementation (once it is available).