Forge Expression Evaluator

A TypeScript library for evaluating Forge language expressions with a browser-compatible UMD bundle.

Installation

``bash
npm install forge-expr-evaluator
`

Usage

$3


`html


`

$3

`javascript
const { ForgeExprEvaluatorUtil } = require('forge-expr-evaluator');

const evaluator = new ForgeExprEvaluatorUtil(datum, sourceCode);
const result = evaluator.evaluateExpression("some Board", 0);
console.log(result);
`

$3


`typescript
import { ForgeExprEvaluatorUtil, DatumParsed } from 'forge-expr-evaluator';

const datum: DatumParsed = {
parsed: {
instances: [/ your data /],
bitwidth: 4
},
data: "..."
};

const sourceCode =
sig Board { ... }
// your Forge signatures and predicates
;

const evaluator = new ForgeExprEvaluatorUtil(datum, sourceCode);
const result = evaluator.evaluateExpression("some Board", 0);
`

API

$3

#### Constructor
`typescript
new ForgeExprEvaluatorUtil(datum: DatumParsed, sourceCode: string)
`

#### Methods
`typescript
evaluateExpression(expression: string, instanceIndex?: number): EvaluationResult
`

$3


- DatumParsed: Data structure containing Forge model instances
- EvaluationResult: Result of expression evaluation (value or error)
- EvalResult: Successful evaluation result (string | number | boolean | Tuple[])

Features

- ✅ Browser-compatible UMD bundle (~688 KiB)
- ✅ TypeScript support with full type definitions
- ✅ Evaluates Forge expressions against model data
- ✅ No external dependencies in the bundle
- ✅ Works with Sterling/Alloy data formats

Development

`bash


Install dependencies

npm install

Build the bundle

npm run build

Run tests

npm test

Serve demo locally

npm run serve
``

License

MIT

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if needed
5. Submit a pull request

Credits

_Note_: The evaluator makes use of a Forge parser built using ANTLR; this is largely taken from
the parser developed by Siddhartha Prasad
with some minor modifications to the grammar.

Related

- Forge Language
- Alloy
- Sterling Visualizer