Push ifs up and fors down: a programming heuristic

The programming heuristic push-ifs-up-fors-down suggests moving conditional logic (if statements) upward towards the caller to centralize branching and improve performance. Meanwhile, iterative loops (for operations) should be pushed downward towards batch processing to minimize unnecessary computations.

The principle applies beyond code optimization. In database query optimization, projections and selections should be performed early to filter data, while joins are deferred to reduce computational overhead. Database execution can also benefit from vectorized or batch processing, which reduces per-call overhead and improves cache efficiency.

Functional programming and category theory also reflect this principle. Pushing ifs up can be seen as restricting to a subobject, where the caller handles the predicate and the callee operates on a subset of inputs. The relationship between filter and map operations demonstrates the algebraic underpinnings of this heuristic, with specific conditions where one can be safely transformed into the other.