Uniqueness type¶

Uniqueness types are implemented in functional programming languages such as Clean, Mercury, SAC and Idris.

Version: v1 · 2026-09-28 · History
Domain-specific #: 12707
Domain group: Applied Sciences & Engineering
Origin domain: Computer Science & Software Engineering
Subdomains: Type Systems, Functional Programming → Computer Science & Software Engineering

Core Idea¶

Uniqueness type is treated here as the recurring computerscienceandinformation identity summarized by this source-grounded definition: Uniqueness types are implemented in functional programming languages such as Clean, Mercury, SAC and Idris. In computing, a unique type guarantees that an object is used in a single-threaded way, with at most a single reference to it. If a value has a unique type, a function applied to it can be optimized to update the value in-place in the object code. Such in-place updates improve the efficiency of functional languages while maintaining referential transparency.

Scope of Application¶

Programming languages. They are sometimes used for doing I/O operations in functional languages in lieu of monads.
Relationship to linear typing. A unique type is very similar to a linear type, to the point that the terms are often used interchangeably, but there is in fact a distinction: actual linear typing allows.
Documented setting. Unique types can also be used to integrate functional and imperative programming.
Introduction. Consider a function readLine that reads the next line of text from a given file.
Introduction. However, using uniqueness typing, we can construct a new version of readLine that is referentially transparent even though it's built on top of a function that's not referentially transparent.

Clarity¶

A clear use of Uniqueness type names the carrier, the operative relation, and the conditions under which the source treats the identity as present. The minimal definition is Uniqueness types are implemented in functional programming languages such as Clean, Mercury, SAC and Idris. The strongest recognition evidence in the frozen account is: Now doImperativeReadLineSystemCall reads the next line from the file using an OS-level system call which has the side.

Manages Complexity¶

Uniqueness type compresses multiple computerscienceandinformation details into a stable diagnostic relation. The source shows both the central mechanism—a unique type is very similar to a linear type, to the point that the terms are often used interchangeably, but there is in fact a distinction: actual linear typing allows a non-linear value to be typecast to a linear form, while still retaining multiple references to it.—and the practical.

Abstract Reasoning¶

Type the carrier. Identify the computerscienceandinformation entities to which the claim applies.
State the relation. Use the source-grounded identity: Uniqueness types are implemented in functional programming languages such as Clean, Mercury, SAC and Idris.
Check operation and conditions. Consider a function readLine that reads the next line of text from a given file.
Demand recognition evidence. Now doImperativeReadLineSystemCall reads the next line from the file using an OS-level system call which has the side effect of changing the current position in the file. 5.

Knowledge Transfer¶

Within the home domain. Knowledge about Uniqueness type transfers literally when a new case preserves the same carrier type, relation, and recognition test. They are sometimes used for doing I/O operations in functional languages in lieu of monads. A unique type is very similar to a linear type, to the point that the terms are often used interchangeably, but there is in fact a distinction: actual linear typing allows a non-linear value to be typecast to a linear form, while still retaining multiple references to it. Beyond the home domain. No canonical.

Relationships to Other Abstractions¶

Current abstraction Uniqueness type Domain-specific

Parents (1) — more general patterns this builds on

Uniqueness type presupposes Type System Domain-specific

A uniqueness type is meaningful only within a type system that tracks exclusive references and update permissions.

Hierarchy paths (2) — routes to 2 parentless roots

Uniqueness type → Type System → Classification

Show alternative path (1)

Neighborhood in Abstraction Space¶

Uniqueness type sits in a sparse region of the domain-specific corpus (66^th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Formal Logic & Language Constructs (20 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-08