Iteratee¶
A resumable stream consumer that processes externally supplied input chunks and returns a result or a continuation requesting more input.
Core Idea¶
An iteratee is a resumable stream consumer: it accepts input supplied by a producer, advances its state, and returns either a completed result or a continuation that needs more input. The producer, often called an enumerator, can read from a file or other source; an optional enumeratee transforms chunks between source and consumer. The identity is this control separation, not any one library's exact state constructors.
Scope of Application¶
Iteratees can count, parse, or transform large inputs without first requiring the whole stream as one value. An original example counts whitespace from file-fed character chunks; a teaching implementation reads one line and returns residual bytes after its delimiter. In a well-designed file enumerator, the producer can close its resource once the consumer finishes, including early completion. That resource guarantee is an implementation property, not automatic for every iteratee.
Clarity¶
Distinguish the consumer, producer, and optional transformer. The consumer does not normally own the file handle in the cited pattern. Continue, Done, Error, NeedIO, and residual-chunk encodings vary by library; only resumption and completion feedback are invariant. A whole-list function or a handle-reading loop may compute the same answer without instantiating this interface.
Manages Complexity¶
The producer can feed small chunks while the consumer carries only its current state, and transformers can filter or decode incrementally. This separates parsing logic from source management. It does not itself guarantee constant memory: a consumer that accumulates an unbounded line or list can still grow without limit, and a parser stopping mid-chunk must preserve the unused suffix.
Abstract Reasoning¶
Each supplied chunk sends the consumer to a new state. If more input is requested, the producer continues; if a result is returned, it can stop. A line reader can finish at a newline while returning the chunk's remaining bytes for the next parser. Exact Haskell constructors differ, but the step-and-resume relation is stable.
Knowledge Transfer¶
For another streaming library, find the resumable consumer state, who supplies input, how completion is signaled, and how errors and unconsumed bytes are handled. Do not equate iteratee with the entire event-time Stream Processing system or with the live Fold prime, which is physical bending. This draft is staged unparented because no current live node supplies the specific consumer-interface genus.
Neighborhood in Abstraction Space¶
Iteratee sits in a sparse region of the domain-specific corpus (77th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.
Family — Program Execution & Runtime Concepts (27 abstractions)
Nearest neighbors
- Stream Abstract Data Type — 0.86
- Rematerialization — 0.83
- Dynamic Problem — 0.82
- Automation — 0.82
- Automaton — 0.82
Computed from structural-signature embeddings · 2026-10-08