Enough grousing... _Haplocheirus_ is a really, really interesting critter. It would seem that the peculiar functionally monodactyl manus of derived alvarezsaurs evolved *after* the forelimb had reduced in size. This is strange, because if the forelimbs were used to rip open insect nests (either mounds or soft wood), why was the reach of the manus *decreased*? This goes against the playbook of extant ant-eaters.
Ant-eaters don't need reach. (They can just walk closer.) They only need power.
The trick is that all extant ones are (to varying degrees, but still) quadrupedal. To be useful in locomotion, forelimbs need a minimum length. Compromises result that the bipedal alvarezsaurids simply didn't need.