# Squiggle language

## Build for development
We assume that you ran `yarn` at the monorepo level. 
``` sh
yarn build
```

`yarn bundle` is needed for a deployment. 

Other: 
``` sh
yarn start  # listens to files and recompiles at every mutation
yarn test
yarn test:watch  # keeps an active session and runs all tests at every mutation
```

## Information
Squiggle is a language for representing probability distributions, as well as functions that return probability distributions. Its original intended use is for improving epistemics around EA decisions.

This package, `@quri/squiggle-lang`, contains the core language of squiggle. The main feature revolves around evaluating squiggle expressions. Currently the package only exports a single function, named "run", which from a squiggle string returns an object representing the result of the evaluation.

If using this package for tests or as a dependency, typescript typings are available and recommended to be used.

This package is mainly written in [ReScript](https://rescript-lang.org/), but has a typescript interface.

ReScript has an interesting philosophy of not providing much in the way of effective build tools. Every ReScript file is compiled into `.bs.js` and `.gen.ts` files with the same name and same location, and then you can use these files in other `.js` files to create your program. To generate these files to build the package, you run `yarn build`.

`.gen.ts` files are created by the [`@genType`](https://rescript-lang.org/docs/gentype/latest/getting-started) decorator, which creates typescript typings for needed parts of the codebase so that they can be easily used in typescript. These .gen.ts files reference the .bs.js files generated by rescript.

### Errors regarding the `rationale` package
You may notice sometimes, that there are errors about the `rationale` package. If you ever get these errors, `yarn build` should fix this issue. These errors occur because `yarn build` also needs to create build files that are in `node_modules`. So if you replace `node_modules` you may need to rebuild to get those files back.

## Distributing this package or using this package from other monorepo packages
As it says in the other `packages/*/README.md`s, building this package is an essential step of building other packages.