# Program

Defined in `program.ts`. The compilation context ([a concept we covered previously](/typescript-deep-dive/project/compilation-context.md)) is represented within the TypeScript compiler as a `Program`. It consists of `SourceFile`s and compiler options.

## Usage of `CompilerHost`

Its interaction mechanism with the OE:

`Program` *-uses->* `CompilerHost` *-uses->* `System`

The reason for having a `CompilerHost` as a point of indirection is that it allows its interface to be more finely tuned for `Program` needs and not bother with OE needs (e.g. the `Program` doesn't care about `fileExists` a function provided by `System`).

There are other users of `System` as well (e.g. tests).

## SourceFile

The program provides an API to get the Source Files `getSourceFiles(): SourceFile[];`. Each is represented as a root-level node for an AST (called `SourceFile`).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://radlohead.gitbook.io/typescript-deep-dive/overview/program.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.