# Vex

> Vex is a TypeScript library for typed spreadsheet formulas over domain objects. A Vex program evaluates at one key of a space of records. It reads fields relative to that key, combines them with the ops of domains (for example 2D vectors), and gives a value or an error value with a code like #REF! or #N/A. Axes evaluate a body at related keys (all, others, other, neighbors, where), and reductions combine the results. A program is plain JSON data.

To write a Vex program as data, follow the JSON Schema of the IR: https://mark1russell7.github.io/vex/ir.schema.json. Then check the program with `parse(text, domains)` of `@mark1russell7/vex`, and evaluate it with `evaluate(expr, { space, origin, domains })`. `explain` gives a trace of each node, with the reads of each reference. A program does not throw: each failure is an error value with a code, a kind, a message, the path of its node, the origin and the focus.

## Docs

- [Tour](https://mark1russell7.github.io/vex/learn/tour/): the builder, one call at a time
- [Concepts](https://mark1russell7.github.io/vex/learn/concepts/): space, origin, focus, address, axis, domain, result
- [Axes](https://mark1russell7.github.io/vex/learn/axes/): the relations between positions, and the reductions
- [Sheets and cycles](https://mark1russell7.github.io/vex/learn/sheets/): named columns that read each other, and #CYCLE!
- [Error values](https://mark1russell7.github.io/vex/learn/errors/): the codes, and how errors go up the tree
- [The IR](https://mark1russell7.github.io/vex/reference/ir/): the kinds of expression, the moves, the axes
- [The API](https://mark1russell7.github.io/vex/reference/api/): the functions and the types of the packages
- [The specification](https://mark1russell7.github.io/vex/spec/): each rule with its requirement ID and its test status

## Optional

- [The Lab](https://mark1russell7.github.io/vex/lab/): edit a program as JSON and evaluate it
- [The source](https://github.com/mark1russell7/vex)