# Pure Functions

> A technique for writing logic as functions whose result depends only on their arguments and which have no side effects.

Record: `architecture:pure-functions`
Kind: technique
Layer: [Computation Core](https://banes-lab.com/records/layer/computation-core.md)
Severity: recommended
Scope: function, domain logic
Canonical: https://banes-lab.com/ontology#architecture-pure-functions

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Referential Transparency](https://banes-lab.com/records/architecture/referential-transparency.md) and before [Immutability](https://banes-lab.com/records/architecture/immutability.md).

## Repair

- Refactored by: Extract Pure Logic, Move IO Outward
- Detected by: side-effect calls inside pure layer
- Violated by: mutation, IO, global reads/writes
- Measured by: pure core ratio
- Enforced by: layer rules, [tests](https://banes-lab.com/records/lexicon/tests.md)

## Requires

- [No Side Effects](https://banes-lab.com/records/lexicon/no-side-effects.md)
- [Explicit Inputs](https://banes-lab.com/records/lexicon/explicit-inputs.md)

## Reinforces

- [Testability](https://banes-lab.com/records/architecture/testability.md)
- [Determinism](https://banes-lab.com/records/architecture/determinism.md)

## Enables

- [Referential Transparency](https://banes-lab.com/records/architecture/referential-transparency.md)

## Conflicts with

- [Hidden IO](https://banes-lab.com/records/lexicon/hidden-io.md)

## In tension with

- [Stateful Operations](https://banes-lab.com/records/lexicon/stateful-operations.md)

## Tensions

- [Pure Functions / Stateful Operations](https://banes-lab.com/records/tension/pure-functions-stateful-operations.md)

## Severity

- [recommended](https://banes-lab.com/records/vocabulary/severity-recommended.md)

## Category

- [Correctness / Determinism / Verification](https://banes-lab.com/records/architecture-category/correctness-determinism-verification.md)

## Linked from

- [Every record has a kind](https://banes-lab.com/software-architecture/principles/every-record-has-a-kind.md)
- [Computation and resource](https://banes-lab.com/software-architecture/principles/computation-and-resource.md)
- [Correctness / Determinism / Verification](https://banes-lab.com/ontology/principles/architecture-category-correctness-determinism-verification.md)
- [Core Vocabulary](https://banes-lab.com/ontology/lexicon/lexicon-category-core-vocabulary.md)
- [Correctness / Determinism / Verification](https://banes-lab.com/ontology/lexicon/lexicon-category-correctness-determinism-verification.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)