Source code in the jq programming language

# Produce a stream of the items in the input SLL.
def items:
  while(.; .next) | .item;

def to_singly_linked_list(s):
  reduce ([s]|reverse[]) as $item (null; {$item, next:.});

# If f evaluates to empty at any item, that item is removed;
# if f evaluates to more than one item, all are added separately.
def map_singly_linked_list(f): to_singly_linked_list( items | f );

{
  "item": 1,
  "next": {
    "item": 2,
    "next": null
  }
}
| reduce items as $item (null; .+$item),
  map_singly_linked_list(- .)