The adapter submodule does not work, I get the following error (in both 
typed and untyped Racket):

    fib.rkt:9:0: module: no #%module-begin binding in the module's language
      in: (module adapter racket/stream (provide stream-first stream-rest 
(rename-out (stream-cons* stream-cons))) (define (stream-cons* make-first 
make-rest/seq) (stream-cons (make-first) (sequence->stream 

If I understand your code correctly, the idea is to define `fibonacci` as a 
stream which returns a stream of Fibonacci numbers, correct? Won't that 
incur a performance loss when used like that in a for-loop if the user does 
not wrap it up in `in-stream`? The idea of `in-fibonacci` was to have a 
form which can be used in a foor-loop the same way `in-naturals` can be. 
Except `in-fibonacci` would have an optional argument at which Fibonacci 
number to start counting.

On Sunday, April 22, 2018 at 10:48:12 AM UTC+2, Philip McGrath wrote:
> I hope there's a better way, but this works. The adapter submodule is 
> needed because the normal `stream-cons` is a macro that expands into some 
> private things that don't have types, and it requires that the rest 
> expression produce a stream, not just any sequence. Note also, if you 
> haven't worked with `racket/stream` before, that the arguments to the 
> normal `stream-cons` are evaluated lazily.

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