[plt-scheme] 2htdp/image: above and friends

i.e., meaning in BSL/+ they should be like + and in ISL too. 


On May 8, 2010, at 1:26 PM, David Van Horn wrote:

> I'd like to suggest that above and friends from the 2htdp/image library change from:
> 
> (above i1 i2 is ...) -> image?
>  i1 : image?
>  i2 : image?
>  is : image?
> 
> to:
> 
> (above is ...) -> image?
>  is : image?
> 
> This is consistent with ISL's +, and it's important for the analogy between numbers and images that the operations remain consistent.
> 
> Also, above (as is) and apply won't work together, which I think was one reason for ISL moving to its current + contract.
> 
> The new function would obey:
> 
> (equal? (above i) i)
> (equal? (above) (circle 0 'solid 'red))
> 
> [Maybe an empty-image binding for that latter value should be in included in the library?]
> 
> David
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