In Flow Core, a Loop does not fundamentally mean “repeat the downstream chain.” Instead, it means repeatedly executing the instruction list inside the current node over a numeric range, and then continuing through Out.

This is the key difference between Loop and Repeat:

Repeat reruns the downstream chain, while Loop reruns the instruction list inside the node itself.

• The purpose of Loop is to perform a deterministic loop within a single flow chain. In the documentation, it is defined as repeating the instruction list over a range, then continuing to the next node when finished.
• By default, it has one In input and one Out output. When created, its default values are From = 0, To = 1, and Step = 1, and it also includes an optional Guard group.

Mechanism

• At runtime, the node first passes through the gate / busy-state logic, and then evaluates the Guard. If the Guard fails, it returns the configured Reject Result, typically Abort or Invalid.

• From, To, and Step are not limited to literal values. They are resolved as integers through FlowValueGetGeneralListCount, which means they can come from a Literal, FlowCoreProcess, Payload, Target, or even directly from the Count of a list.

• The loop condition is straightforward:

  • When Step > 0, the loop continues while index < to
  • When Step < 0, the loop continues while index >= to
  • When Step == 0, the loop becomes infinite until an instruction returns Break or Restart

• On each iteration, the current index is written into the Index Payload. If Loop Index Enabled is turned on, the current index is also written into an additional int target. Even if Blackboard write-back is disabled, the payload index always exists.

• Check Instruction return values have special meanings inside a loop:

  • Break: exits the entire loop and continues through Out
  • Restart: re-resolves From / To / Step and restarts from the beginning
  • LoopContinue / Continue: proceeds to the next iteration

UI

• In the editor, this node appears under the Loop menu entry, with its own Loop color theme and a ♾️ icon style.

• The node body is typically read in this order: Guard, Loop Settings, and Instructions. The Loop Settings section includes From, To, Step, and Index Target, along with a collapsible summary, copy/paste buttons, and a warning when Step = 0.

• The busy-state hints are:

  • Abort: terminates the current flow chain
  • Queue: waits until the previous execution finishes
  • Bypass: skips the current node
  • Invalid: ends the current branch

  These are the standard invoke semantics inherited by Loop. They are not unique loop behaviors.

Examples

• Index-based iteration Set From = 0, To = listCount, and Step = 1. On each iteration, use PayloadIndex to access the corresponding list element.
• Reverse traversal Set From = lastIndex, To = 0, and Step = -1. This is useful when you need to scan from the end of a list toward the beginning.