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The Coalton (package ...) Form

In Coalton, the package form is used to define a package by specifying which symbols to import, and which symbols to export.

The form also establishes the current package: any definitions that follow (package <name>) will be contained within that package. It effectively combines the functions of defpackage and in-package in Common Lisp.

Defining a Package

A package in Coalton is defined using the package form. The syntax is:

(package <package-name>
  (import <other-package-name>
          (<other-package-name2 as <other2>)
          ...)
  (import-from <other-package-name>
          <symbol1>
          <symbol2>
          ...)
  (export <symbol3>
          <symbol4>
          ...))

An example:

(package my-package
  (import coalton-library/list
          (coalton-library/vector as vec))
  (import-from coalton-library/char
          upcase
          downcase)
  (export sum-even-numbers))

Importing Dependencies

You can import dependencies for your package using the import and import-from forms.

The import form allows you to specify which packages your package depends on. You can also rename imported packages using the as keyword:

(package my-package
  (import coalton-library/list as list)
  (export sum-even-numbers))

The import-from form specifies which symbols from an imported package should be made available within your package:

(package my-package
  "Package documentation string (optional)"
  (import-from coalton-library/list
    filter)
  (export sum-even-numbers))

Exporting Definitions

You can export definitions from your package using the export form. This allows other packages to use these definitions.

For example, if you have a function sum-even-numbers that you want to make available for use by other packages:

(package my-package
  (import coalton-library/list)
  (export sum-even-numbers))

In this case, the sum-even-numbers symbol will be exported from your package and can be used by other packages that import your package.

Lisp Interoperability

Packages defined by package are fundamentally structurally compatible with Lisp packages, as the import, import-from, and export forms evaluate unambiguously to Lisp defpackage counterparts :use, :local-nicknames, and :export.

  • Any given Coalton package can be imported into any Lisp package.
  • Any given Lisp package be imported into any Coalton package.
  • The name of a coalton-defined package be the same whether importing into Coalton or Lisp.
  • Coalton packages are compatible with utilities such as uiop:define-package's :mix-reexport clause.