[racket] combine-in doesnt combine?

From: Carl Eastlund (cce at ccs.neu.edu)
Date: Tue Oct 8 19:32:23 EDT 2013

It does accept a union, but a module import is a finite map (from
identifiers to their definitions), not just a set.  The union is only
well defined if all duplicated keys map to the same values.  In this
case, one import maps image? to the definition in htdp, and the other
maps image? to the definition in 2htdp.  The union is not well
defined, so combine-in must fail.

On 10/8/13, Stephen Chang <stchang at ccs.neu.edu> wrote:
> What is the intended use case of combine-in? The docs says it does a
> union but that doesnt seem to be true.
> (require (combine-in lang/htdp-beginner 2htdp/image))
> module: identifier already imported from a different source in:
>   image?
>   (rename 2htdp/image image? image?)
>   (rename lang/htdp-beginner image? image?)
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Carl Eastlund

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