Reconstruction.traceback: def of bend-edit-distance@0.2.2.0
Import: import bend-edit-distance@0.2.2.0/src/Reconstruction.bend as Reconstruction
Lines 79-100 of bend-edit-distance@0.2.2.0/src/Reconstruction.bend: https://jend.leeeet.dev/read.txt?path=bend-edit-distance@0.2.2.0/src/Reconstruction.bend&start_line=79&end_line=100

import Base
import bend-edit-distance@0.2.2.0/EdlibTypes.bend as E

# Rows and their operations are reversed so left moves consume the current
# row directly. Entering the row above skips only its unused right suffix.
# Including boundary rows/columns handles all-insertion/deletion paths.
def traceback(fuel: Nat, current: List<&2, TraceCell>,
               previous: List<&2, List<&2, TraceCell>>, +width: Nat,
               +column: Nat, operations: List<&2, E.Operation>) -> List<&2, E.Operation>:
  match fuel current previous:
    case 0n _ _:
      operations
    case 1n+p _ Nil{}:
      List.append(&2, E.Operation, List.replicate(E.Operation, column, E.Delete{}), operations)
    case 1n+p Nil{} _:
      operations
    case 1n+p TraceCell{_, E.Insert{}} <> _ row <> rest:
      traceback(p, List.drop(&2, TraceCell, row, Nat.sub(width, column)),
        rest, width, column, E.Insert{} <> operations)
    case 1n+p TraceCell{_, E.Delete{}} <> tail +rows:
      traceback(p, tail, rows, width, Nat.sub(column, 1n), E.Delete{} <> operations)
    case 1n+p TraceCell{_, operation} <> _ row <> rest:
      +next_column = Nat.sub(column, 1n)
      traceback(p, List.drop(&2, TraceCell, row, Nat.sub(width, next_column)),
        rest, width, next_column, operation <> operations)

Uses (8):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.append
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.drop
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.replicate
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.sub
  https://jend.leeeet.dev/definition.txt?path=bend-edit-distance@0.2.2.0/EdlibTypes.bend&name=Operation
  https://jend.leeeet.dev/definition.txt?path=bend-edit-distance@0.2.2.0/src/Reconstruction.bend&name=TraceCell