Folds a pair-returning function over a list and returns the last emitted value; the two-argument form seeds the state with the first list element
FoldPair[f, y0, list]
FoldPair[f, y0, list, g]
FoldPair[f, {a0, a1, a2, …}]
FoldPair[{p[#1, #2], q[#1, #2]}&, {a, b, c}]
→ p[q[a, b], c]FoldPair[{p[#1, #2], q[#1, #2]}&, u, {1, 2, 3}]
→ p[q[q[u, 1], 2], 3]FoldPair[{p[#1, #2], q[#1, #2]}&, u, {1, 2, 3}, Last]
→ q[q[q[u, 1], 2], 3]