6.3.30  Folding sequences

The foldl (left-fold) and foldr (right-fold) commands take an infixed operator or function of two variables and apply them across a sequence of inputs through left and right association.

• foldl takes a sequence of arguments:
  • R, an infixed operator or function of two variables.
  • I, an initial value.
  • a₁,a₂,…, a_k, an arbitrary number of additional arguments.
• foldl(R,I,a₁,…,a_k) returns R(… R(R(I,a₁),a₂)…,a_k).
• foldr takes a sequence of arguments:
  • R, an infixed operator or function of two variables.
  • I, an initial value.
  • a₁,a₂,…,a_j, an arbitrary number of additional arguments.
• foldr(R,I,a₁,a₂,…,a_k) returns R(a,…(R(a₁,R(a₂,… R(a_k−1,R(a_k,I)))).

Examples

which is equal to 2⁽³⁵⁾.

which is equal to 3⁽⁵²⁾.