Re: [Scheme-reports] Identifiers imported "by reference or value"?

[Alex Shinn <alexshinn@x>]

On Tue, Feb 4, 2014 at 12:04 AM, Marc Nieper-Wißkirchen <marc.nieper@x> wrote:

 

Related to this is one paragraph in 5.1:

It says:

Import declarations and definitions cause bindings to be
created in the global environment or modify the value of
existing global bindings. The initial environment of a pro-
gram is empty, so at least one import declaration is needed
to introduce initial bindings.

First of all, when (outside of a REPL) is it possible for an import declaration to modify (the value) of existing global bindings? Is this a correct library?

(import (scheme base))

(begin

  (define x 1))

(import (only (other-lib) x)

Or does it count against the fact that an imported binding is not allowed to be redefined or mutated (although the identifier is not yet imported in the begin form)?

This is an error as described in 5.2:

  [..] it is an error to import the same identifier more than once with

  different bindings, or to redefine or mutate an imported binding with

  a definition or with set!

The order of the import and definition don't matter.  Section

5.6.1 specifically lists two possible implementations of

libraries, in one of which all imports are performed before

the expressions from begin and include are expanded.

-- 

Alex

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