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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/list
          (coalton/vector as vec))
  (import-from coalton/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/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/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/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.

Exported top-level definitions should have a matching declare. Missing declarations currently signal coalton:deprecation-warning and can be promoted to errors with Coalton's :deprecation-warnings-as-errors configuration option.

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.