This module contains versions of functions from Data.RBR, generalized to work with a subset of the fields of a Record or the branches of a Variant.

Besides working with subsets of fields and branches, this module is useful for another thing. The equality of type-level trees is unfortunately too strict: inserting the same elements but in different order can result in structurally different trees, which in its turn causes annoying errors when trying to combine Records, even as they have exactly the same fields.

To solve these kinds of problems, functions like projectSubset can be used to transform Records indexed by one map into records indexed by another.

For example, consider this code:

>>> :{
    prettyShow_RecordI $
      liftA2_Record
        (\_ x -> x)
        ( id
            $ S.projectSubset @(FromList ['("bar", _), '("foo", _)]) -- rearrange
            $ insertI @"foo"
              'a'
            $ insertI @"bar"
              True
            $ unit
        )
        ( id
            $ insertI @"bar"
              True
            $ insertI @"foo"
              'a'
            $ unit
        )
:}
"{bar = True, foo = 'a'}"

If we remove the projectSubset line that rearranges the structure of the first record's index map, the code ceases to compile.

Note: There are functions of the same name in the Data.RBR module, but they are deprecated. The functions from this module should be used instead, preferably qualified. The changes have to do mainly with the required constraints.