It depends on what kind, Haywood. Of the ones I'm familiar with, Polyanthus will work in both, but blooms more in sun. Afternoon shade will help it take a Maryland summer better, though. Fairy Primrose (P. malacoides) does best in bright to dappled shade, as does German Primrose (P. obconica). Other members of this site will probably be better suited to answering for the many other species of Primula. Evening Primrose (Oenothera species) always do best in full sun.

The British'common' primrose, Primula vulgaris, will grow in full sun in a wet, grassland situation but is really a woodland plant for moist soils and dappled shade.