# Epsil Epsil is a programming language for scientific computing, built on the Compute Engine. :::warning[Experimental] Epsil is available as an **experimental** entry point. Its syntax and semantics may change between releases while the language is being exercised in notebooks and other applications. ::: Epsil is embedded from JavaScript through the `@cortex-js/compute-engine/epsil` entry point: ```js import { ComputeEngine, executeEpsil } from "@cortex-js/compute-engine/epsil"; const ce = new ComputeEngine(); const { value, diagnostics } = executeEpsil(ce, "1 + 2"); ``` Here is "Hello World" in Epsil. Edit the code and press **Run** (or ⌘/Ctrl+Enter) — the result is the value of the last statement, shown as an Epsil value and as its underlying MathJSON. ```epsil-live "Hello World" ``` Epsil is **symbolic by default**: expressions stay exact unless you ask for a numeric approximation with `N()`. ```epsil-live Simplify(2 + 3x^3 + 2x^2 + x^3 + 1) ``` Values have a type, and strings support `\(…)` interpolation: ```epsil-live let x = 2^11 - 1 "\(x) has type \(Type(x))" ``` Errors are ordinary values, so a program never throws to its host — a problem surfaces as an `["Error", …]` value or a diagnostic: ```epsil-live const answer = 42 answer = 0 ``` ## Start Here Follow the **five-minute getting-started guide** — try the REPL, run a source file, and embed Epsil in JavaScript. Explore **complete Epsil programs** for symbolic computation, collections, calculus, linear algebra, strings, and more. Use the **CLI and interactive REPL** from a terminal. Coming from **Python**? Translate your idioms — and learn the three reflexes that silently do the wrong thing. Coming from **Mathematica**? Most of the mental model carries over; here is what changes. Writing Epsil with an LLM? Give it the **language card for AI agents** — a condensed, machine-verified reference. Connect ChatGPT, Claude, or another AI assistant to Epsil with the built-in **MCP server** — exact math as a tool call. ## Language Reference Read more about the **formal syntax of Epsil** — statements, primaries, calls and indexing. **Literals** — numbers, strings, symbols, and `$…$` LaTeX islands. **Operators** — arithmetic, logic, relational, and the pipeline operator. **Control flow** — `if`/`else`, `match`, loops, blocks, and functions. **Declarations** — binding names with `let` and `const`. **Types** — annotations, named types, effects, and absence values. **Comments** — line and block comments. **Pragmas** — parser directives embedded in the code. ## Collections Epsil has literal syntax for the Compute Engine's collections. **Lists** are ordered and 1-indexed with `xs[i]`: ```epsil-live [3, 5, 7, 11] ``` **Sets** are unordered collections of unique elements: ```epsil-live {3, 5, 7, 11} ``` **Dictionaries** are sets of key/value pairs. The empty dictionary is `{->}`: ```epsil-live {one -> 1, two -> 2} ``` Read more about **lists, sets, tuples and dictionaries**. ## Future Directions Several keywords are **reserved but not designed** — they are held so that a future version of Epsil can introduce them without breaking existing programs, and using one as an ordinary name today is an error. None of the following are part of the language yet: - **Modules and imports** — `import`, `export`, `module`. - **Error-handling keywords** — `try`, `catch`, `throw`. In Epsil, errors are ordinary values, so these are not needed for the current design. - **Concurrency** — `async`, `await`, `parallel`. - **Macros** and compile-time metaprogramming. If you need a symbol whose name collides with one of these reserved words, use the verbatim form (`` `match` ``).