This instance handles product types and is pretty important. We need to check that recursive calls to gConfigSource generate sub-trees, and then we merge the sub-trees.

You may wonder what happens if there is a Pure value in one of the record fields, well that would be represented like so:

Free $ M.singleton fieldName (Pure value)

since we need to account for the key corresponding to the record field. So we really should never hit a case were a recursive call to gConfigSource yields a raw Pure.

Since: 0.0.2.0

Sum types should represent base values, so Free M.empty is the right thing to do here, although we should probably never hit this case, since sum types should be nested under record fields as base values.

Since: 0.0.2.0

This is the "base case", since GHC.Generics don't recurse the generic represetation multiple levels, a is just a plain type. Therefore we call configSource on it. a may be another nested record, in which case gParseConfig will probably get called again, but for the generic representation of a sub-tree. It will do this until it finds a ConfigSource instance for Value which will just add a 'Free Data.Map.empty' (indicating a hole to be filled when we fetch the configuration).

Since: 0.0.2.0

This is the data constructor case, if we are dealing with a ConfigRoot instance, then we have to create an extra layer with the "root key" as a key and then a subtree (calculated by recursively calling gConfigSource) as the value.

Since: 0.0.2.0

This is the type constructor case, if we are dealing with a ConfigRoot instance, then we have to create an extra layer with the "root key" as a key and then a subtree (calculated by recursively calling gConfigSource) as the value.

Since: 0.0.2.0

This instance is important because it does the work of pulling off the field selector name, and creating a sub-tree under that key by calling gConfigSource recursively. If there is a default for that selector then no sub-tree is created, instead we insert a "placeholder" value tagged by Pure to represent that it is the end of the tree.

We detect if a default exists by calling defaults from the DefaultSource instance on the selector, defaults is of type Text -> Maybe Text, so the Nothing case indicates no default.

Since: 0.0.2.0