listextenddest

Listextenddest is a term used in discussions of functional programming and data structures to describe a pattern or utility that extends a list by associating each element with a destination descriptor. The name combines “list,” “extend,” and “dest,” reflecting its purpose: to prepare a list for routing, serialization, or dataflow analysis by tagging elements with a destination.

The exact semantics of listextenddest vary by library or language. In the common interpretation, it takes a list L and a destination descriptor D and returns a new list where each element x in L is paired with D, either as (x, D) or as an annotation attached to x, depending on the representation. Some variants attach D only to the tail, others create a parallel structure mapping elements to D.

Usage scenarios include preparing messages for routing in a pipeline, building destination-aware graphs, or tagging data for later dispatch. It can simplify consumers that need to know where to send each item without altering the underlying values.

In Lisp-like languages, listextenddest can be implemented with map or list-transform primitives, for example by mapping a function over L that produces (cons x D) or (list x D). Considerations include memory overhead, immutability, and how destination metadata is stored and accessed. Some designs seek to minimize allocations by using lightweight wrappers or metadata fields.

See also: map, cons, metadata, tagging, data routing, dataflow, serialization.