On Tue, Feb 4, 2014 at 4:16 PM, Marc Nieper-Wißkirchen < [email protected]> 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 ofexisting global bindings. The >>> initial environment of a pro-gram is empty, so at least one import >>> declaration is neededto introduce initial bindings. * >>> >> [..] 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. >> > > Great! This means that my problematic example does not work, which is good. > > Which leaves the question to which situations the possibility of modifying > an existing global binding as mentioned in the quoted paragraph from 5.1. > actually applies. > The only place left, which you already pointed out, the REPL. Note also this is an implementation detail. As the passage states, it _may_ modify _or_ create, but the programmer can't assume either. Specifically section 5.7 discusses the REPL, and the possibility of implementations for which all possible variables are already bound to locations. Both of these passages come from R5RS, in deference to such implementations. -- Alex
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