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Editorial Team
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Asked: 2026-06-11T23:32:16+00:00

Using the GNAT compiler, when I try to compile or check semantic on the

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Using the GNAT compiler, when I try to compile or check semantic on the following files, I get some variation of the error package "Foo" does not allow a body. I’m new to the language and can’t find an answer to this seemingly basic problem anywhere on the Internet. Please advise.

foo.ads

package Foo is
   type Shape_Enum is (Circle, Triangle, Rectangle);
end Foo;

foo.adb

package body Foo is
   procedure Foo is
      MyShape : Shape_Enum;
   begin
      MyShape := Rectangle;
   end Foo;   
end Foo;
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1 Answer

  1. Editorial Team

    A package is only allowed to have a body if the specification includes something that requires a body. (This avoid problems where an optional body might accidentally be left out of a build.)

    You have a procedure in the body of the package (Foo.Foo), but there’s no way to call it.

    If you add a declaration:

    procedure Foo;

    to the specification, that should (a) fix the error, and (b) permit the procedure to be called by clients of the package. Or you can use pragma Elaborate_Body; to require it to have a body if you don’t want the procedure to be visible to clients.

    Incidentally, there’s nothing special about a procedure with the same name as the package that contains it (unlike in C++, where such a function is a constructor for the containing class). It would probably be clearer to use a different name.

    See section 7.2 of the Ada Reference Manual (I’m using a recent draft of the 2012 standard):

    A package_body shall be the completion of a previous
    package_declaration or generic_package_declaration. A library
    package_declaration or library generic_package_declaration shall not
    have a body unless it requires a body; pragma Elaborate_Body can be
    used to require a library_unit_declaration to have a body (see 10.2.1)
    if it would not otherwise require one.

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