[plt-dev] Q. about contract of drscheme:eval:expand-program

The contract for drscheme:eval:expand-program specifies that it  
accepts an 'iter' argument fulfilling this contract:

(-> (or/c eof-object? syntax? (cons/c string? any/c))
     (-> any)
     any)

I'm wondering why the (cons/c string? any/c) is in there.  The  
documentation states:

The first argument to iter is the expanded program (represented as  
syntax) or eof. The iter argument is called for each expression in the  
expanded program and once more with eof, unless an error is raised  
during expansion. It is called from the user’s thread. If an exception  
is raised during expansion of the user’s program, iter is not called.  
Consider setting the exception-handler during init to handle this  
situation.

... so, under what circumstances does expand-program call iter with  
(cons/c string? any/c) ?


John

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