‘extent’ implementation is misleading, never uses parallel fold

[glts]

huri.core/extent uses clojure.core.reducers/fold in its implementation. However, no possible inputs can trigger actual parallel folding; extent always degenerates to plain reduce. This is because all inputs result in r/fold being applied to a sequence, which is not a foldable collection.

Furthermore, if the parallel fold were actually triggered, extent would always throw an exception because the combining function (here same as the reducing function) doesn’t work.

To address this the alternatives are:

• Replace r/fold with reduce.
• Allow foldable inputs to be passed through to r/fold and supply an appropriate combining function.