Re: linear -> affine and shapes are immutable

*Jussi Piitulainen* 13 Nov 2001 07:22 UTC

xxxxxx@math.purdue.edu writes:
> I would suggest that "affine" would be a better name than
> "linear" for the properties of the access functions. Linear
> is OK (as in linear as opposed to quadratic polynomials), but in
> this context with all the "vector"s and "array"s, I think affine
> would be better.
Interesting. A book on Java 2D graphics defines affine transformation
as "one in which parallel lines are still parallel after ...".
I cannot judge which is better. I don't want to put in anything about
parallel lines. Does "each index is a sum of multiples" match "affine"
at least as well as it matches "linear"?
> Also, instead of saying
>
> It is an error to store anything in an element of a shape.
>
> can one just say that "Shapes are immutable"?
We might indeed want to specify the latter. It is not so now: any
array of the right form can be used as a shape, `make-array' just
stores it into the new record, the _shape_ remains happily mutable -
it is only the array that breaks horribly if you mutate its shape.
Choices are to specify that `array-shape' returns an immutable array
(copy if needed) or to leave it as an implementation quality issue.
--
Jussi