aws/pagination

Fold-style paginator helper for Smithy @paginated operations.

The codegen-emitted paginate_<op> functions are thin wrappers over fold. Each generated paginator:

Builds a step(cursor) -> Result(#(items, next_cursor), e) closure that injects the cursor into the typed input via the inputToken field, invokes the operation, and projects the items + outputToken fields out of the typed output.
Calls fold(acc, step, reducer) to drive the loop until the step returns None for the next cursor.

The helper deliberately doesn’t depend on gleam_yielder or any lazy-stream package: a fold over a typed accumulator handles every paginated-list use case (count, collect, find-first, …) without forcing a runtime dependency or special evaluation strategy.

Values

fold

</>

pub fn fold(
  acc acc: a,
  step step: fn(option.Option(cursor)) -> Result(
    #(List(item), option.Option(cursor)),
    error,
  ),
  reducer reducer: fn(a, List(item)) -> a,
) -> Result(a, error)

Drive a Smithy @paginated operation to completion, folding each page’s items into acc via reducer. The step closure receives the cursor returned by the previous page (or None on the first call) and must return #(items, next_cursor) for the page it just fetched. The loop stops when step returns None for the next-cursor — the canonical Smithy signal that pagination is exhausted. Errors from step propagate verbatim.

cursor is parametric: most AWS services use String (NextToken, Marker, …) but some carry richer values (DynamoDB’s LastEvaluatedKey is a Dict(String, AttributeValue)). The helper stays agnostic — the codegen-emitted paginate_<op> wrapper instantiates cursor to match the operation’s input/output token types.