> For the complete documentation index, see [llms.txt](https://he-said.tdreyno.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://he-said.tdreyno.com/type-safety-and-terms.md).

# Type Safety and Terms

he-said is designed around strongly typed terms and relation signatures.

## Why Terms Are Symbols

term() returns a unique symbol branded with T.

Benefits:

* no accidental string key collisions
* clear, static pairing between terms and values
* safe relation signatures through TypeScript

## Predicates with is

termValue.is(predicate) creates a derived term with additional unary filtering.

```ts
import { term } from "@tdreyno/he-said"

type User = { id: string; suspended: boolean }

const user = term<User>()
const activeUser = user.is(candidate => !candidate.suspended)
```

Derived terms can be reused in relation and equality expressions.

## Equality and Binding

eq(leftTerm, rightTermOrValue) supports:

* term-to-term equality
* term-to-value equality

If one side is not bound in the current environment, evaluation may bind it.

## Compile-Time Assertions

This repository includes compile-time type tests in src/core/algebra.typecheck.ts.

Run:

```bash
npm run test:types
```


---

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