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120 lines
4.5 KiB
Markdown
120 lines
4.5 KiB
Markdown
---
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layout: developer-doc
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title: Modules
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category: semantics
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tags: [semantics, modules, runtime]
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order: 6
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---
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# Modules
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Modules are the basic way to organize code into smaller, semantically-relevant
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parts. The following is the description of the semantics of Enso modules.
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<!-- MarkdownTOC levels="2,3" autolink="true" -->
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- [Introduction](#introduction)
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- [Referring to Modules](#referring-to-modules)
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- [Module-Level Methods](#module-level-methods)
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- [Types](#types)
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- [Referent Name Resolution](#referent-name-resolution)
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- [Referent Names in Method Calls](#referent-names-in-method-calls)
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- [Importing & Exporting Methods](#importing--exporting-methods)
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- [Export Statement Semantics](#export-statement-semantics)
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- [Project Main Module](#project-main-module)
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<!-- /MarkdownTOC -->
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## Introduction
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There's a one-to-one correspondence between source files and modules. Moreover,
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a module's name is the same as that of the corresponding source file. That also
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implies, that an Enso source file name must be a valid referent name. Modules
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are first-class objects, meaning they can be assigned to variables and passed as
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function parameters.
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## Referring to Modules
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Modules can be imported into the current scope by using the `import` statement.
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To import a module, one must provide it's full qualified path. A qualified path
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of a module is a number of `.`-separated segments, where:
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1. The first segment is the name of the project in which the module is located.
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2. The following segments are the names of directories between `src` and the
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source file being imported.
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3. The last segment is the name of the source file, with the `.enso` extension
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stripped.
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For example, a qualified name of a module corresponding to the file
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`src/Foo/Bar/Baz.enso` in project `Project` is `Project.Foo.Bar.Baz`.
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Whenever a module is imported, its name (either the last segment of the
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qualified name or the name it was renamed to), becomes available in the
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importing scope as a value.
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Moreover, the current module is always visible in the scope under its file-based
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name, and as the special variable `here`.
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## Module-Level Methods
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A method defined without an explicit `this` reference, or with `this` explicitly
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set to the current module, becomes a module-level method. Such a method can be
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called by passing the module as the `this` parameter. Such methods can also be
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called by importing modules and using the imported module in place of `this`.
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## Types
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From the perspective of accessing them through imports, there is no difference
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between a `type` constructor definition and a module-level method. Both can be
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accessed in exactly the same ways both from inside the module and from the
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importing modules.
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## Referent Name Resolution
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Referent names are resolved in a special way, by finding the relevant name among
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imported modules and items explicitely imported from them. Imported items may be
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one of the following: modules, types, module-level methods and polyglot symbols.
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The order of resolving names is as follows:
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1. Symbols defined in local (function or block) scopes.
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2. Symbols defined in the current module.
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3. Names of imported modules.
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4. Names explicitly imported from modules.
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If there's an ambiguity at any level, an error is reported.
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## Referent Names in Method Calls
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If a referent name is used as the method name in method call syntax, it is not
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subject to referent name resolution and is instead treated as though it was not
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referent in this position.
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## Importing & Exporting Methods
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Methods defined both on the module and on other types are always imported and
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exported automatically whenever the module is imported or exported. There is
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currently no plan to allow hiding methods from imported / re-exported modules,
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but this decision will be revised after a sufficiently large corpus of Enso code
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exists.
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## Export Statement Semantics
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A qualified export statement only exports the name of the exported module
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(possibly renamed).
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In a `from` export, any mentioned items become available as though they were
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defined in the exporting module.
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Please note it is explicitly forbidden for export statements across modules to
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form a cycle. If export statements cycle is detected, a compile error will be
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reported.
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## Project Main Module
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The module `Main` in any project is treated specially, as the main entry-point
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to the library. Therefore, using the bare project name in an import statement
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(e.g. `import My_Project`) is equivalent to importing the `Main` module with the
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proper rename (e.g. `import My_Project.Main as My_Project`). This syntax sugar
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works with any kind of import or export statement.
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