[racket] combine-in doesnt combine?

No images in 2htdp and htdp differ and there's some funny exporting/importing going on to get the predicates into the right place because they also work on copied/pasted images. 


On Oct 8, 2013, at 7:51 PM, Stephen Chang <stchang at ccs.neu.edu> wrote:

> Ok, I didn't realize they were different functions. I thought the htdp langs just imported from 2htdp/draw.
> 
> 
> On Tue, Oct 8, 2013 at 7:32 PM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> 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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