enso/docs/syntax/imports.md

---
layout: developer-doc
title: Imports and Exports
category: syntax
tags: [syntax, imports, modules]
order: 4
---

# Imports and Exports

In order to properly modularise and work with Enso code, the language provides a
robust mechanism for importing code from modules, and also re-exporting that
code from modules.

<!-- MarkdownTOC levels="2,3" autolink="true" -->

- [Qualified Names](#qualified-names)
- [Import Syntax](#import-syntax)
  - [Qualified Imports](#qualified-imports)
  - [Unqualified Imports](#unqualified-imports)
- [Imports with multiple targets](#imports-with-multiple-targets)
- [Export Syntax](#export-syntax)
  - [Qualified Exports](#qualified-exports)
  - [Unqualified Exports](#unqualified-exports)
  - [Visibility of Export Bindings](#visibility-of-export-bindings)
  - [Implicit exports](#implicit-exports)
    - [Defined entities in a module](#defined-entities-in-a-module)
    - [Synthetic module](#synthetic-module)
- [Exports with multiple targets](#exports-with-multiple-targets)

<!-- /MarkdownTOC -->

## Qualified Names

In the following text, **entity** shall denote a module, a method (instance,
static, extension, conversion or foreign), type, or a type constructor.

Both imports and exports require the use of qualified entity names. A qualified
name consists of the library namespace (usually organization under which its
published) and the library name, followed by module names mirroring the source
tree of the library, followed by an entity name within that module. For example
the file `src/Stuff/Things/Util.enso` inside the library `My_Lib` published by
the user `wdanilo` would have the following qualified name:
`wdanilo.My_Lib.Stuff.Things.Util` and the type `My_Type` within that module
would have the qualified name `wdanilo.My_Lib.Stuff.Things.Util.My_Type`. To
facilitate library renaming (or deciding on the publishing organization later in
the development cycle, or working on a project that won't be published) it is
possible to use the keyword `project` instead of namespace and project name, to
import a file in the same project. Therefore, the file
`src/Varia/Tools/Manager.enso` in `My_Lib` published (or not) by `wdanilo` may
use `project.Stuff.Things.Util` to refer to the previously mentioned file.

Currently, the `project` keyword works only in import and export statements.
Note that it is possible to export a symbol from the current project with the
`project` keyword without first importing it.

## Import Syntax

There are two main ways of importing a module into the current scope.

### Qualified Imports

These imports consist of the word `import` followed by a qualified name of an
entity. This can be optionally followed by the `as` word, and a referent name of
the entity as it should be visible in the importing scope.

The only name brought into scope by such an import is the name of the entity (or
the name provided after the `as` keyword, if provided).

### Unqualified Imports

Unqualified imports are broken up into three main categories:

1. **Unrestricted Imports:** These import all symbols (entities) from the module
   (or from a type) into the current scope. They consist of the keyword `from`,
   followed by a qualified module name, followed by an optional rename part
   (using the `as` keyword), then the keywords `import all`. For example:
   ```
   from Standard.Base.Data.List as Builtin_List import all
   ```
2. **Restricted Imports:** These import a specified set of names for use as
   automatically resolved referent names. They consist of the keyword `from`,
   followed by a qualified module name (with optional `as`-rename), then the
   word `import` followed by a coma-separated list of referent names to be
   imported. For example:
   ```
   from Standard.Base.Data.List import Cons, Nil
   ```
3. **Hiding Imports:** These are the inverse of restricted imports, and import
   _all_ symbosl other than the named ones. They consist of the `from` keyword,
   followed by a qualified module name (with optional `as`-rename), then the
   words `import all hiding`, followed by a coma-separated list of referent
   names to be excluded from the import. For example:
   ```
   from Standard.Base.Data.List import all hiding Cons, Nil
   ```

Imports in Enso _may_ introduce ambiguous symbols, which is treated as a
compilation error. Ideally, the error should be delayed until one of the
ambiguous symbols is _used_ in Enso code.

## Imports with multiple targets

Import of one symbol can resolve to multiple targets in case of extension or
conversion methods. For example, the following import in `Main.enso`:
`A_Module.enso`:

```
type My_Type
type Other_Type
My_Type.method = 42
Other_Type.method = 42
```

`Main.enso`:

```
import project.A_Module.method
```

imports both `My_Type.method` and `Other_Type.method` methods.

Note that `import project.A_Module.My_Type.method` would lead to a compilation
error, as it is only possible to import constructors from a type, not methods.

## Export Syntax

In order to allow for easy composition and aggregation of code, Enso provides
its users with a mechanism to _export_ imported elements from modules. They
appear in Enso as follows:

### Qualified Exports

These exports consist of the word `export` followed by a qualified name of an
entity. This can be optionally followed by the `as` word, and a referent name of
the entity as it should be visible in the exporting scope.

The only name brought into scope by such an export is the name of the entity (or
the name provided after the `as` keyword, if provided).

### Unqualified Exports

Unlike imports, exports cannot be used with the `all` and `hiding` keywords. So
the only supported syntax is to export a list of names with _restricted
exports_.

**Restricted Exports:** These export a specified set of names, behaving as
though they were redefined in the current scope. They consist of the keyword
`from`, followed by a qualified module or type name (with optional `as`-rename),
then the word `export` followed by a coma-separated list of names to be
exported. For example:

```
from Standard.Base.Data.List export Cons, Nil, from_vector
```

In essence, an export allows the user to "paste" the contents of the module or
type being exported into the module declaring the export. This means that
exports that create name clashes must be resolved at the _export_ site.

### Visibility of Export Bindings

Bindings exported from a module `X` are available in an identical fashion to
bindings that are _defined_ in the module `X`.

### Implicit exports

The compiler inserts implicit exports for entities defined in a module and for
submodules of a _synthetic module_. A synthetic module is basically a directory
in the source structure.

#### Defined entities in a module

Entities defined in a module are automatically exported from the module. This
means that the following modules are semantically identical:

```
type My_Type
method x = x
```

```
export project.Module.My_Type
export project.Module.method
type My_Type
method x = x
```

#### Synthetic module

Consider a project named `Proj` with the following source structure:

`Proj/src/Synthetic_Mod/Module.enso`:

```
type My_Type
```

`Proj/src/Main.enso`:

```
import project.Synthetic_Mod.Module.My_Type
```

We can import submodules of `Synthetic_Mod`, because the compiler automatically
inserts exports for them. Internally, `Synthetic_Mod` is represented as a module
with single export:

```
export project.Synthetic_Mod.Module
```

## Exports with multiple targets

Export of a single symbol can be resolved to multiple targets (entities) in case
of extension or conversion methods. Similarly to
[imports with multiple targets](#imports-with-multiple-targets), the following
export in `A_Module.enso`:

```
export project.A_Module.export
```

exports both `My_Type.method` and `Other_Type.method` methods.