> On Jul 31, 2017, at 10:23 PM, Daryle Walker via swift-evolution
> <[email protected]> wrote:
>
> Could we do better than simple repetition? What if we define a “$$n” unit,
> where “n” is a nonnegative integer. For each comma-separated item, the unit
> will be replaced by increasing compiler-constant integers from zero. If using
> an expression, maybe you can call a function on the double-dollar value to
> get your own custom values there. This can be expanded to types once
> value-based generic parameters get added.
>
> When there are nested #dup calls, the double-dollar unit refers to the
> counter for the innermost #dup. Maybe there can be a triple-dollar unit for
> the immediately enclosing #dup. Even quadruple- or more-dollar units for the
> outer levels. (Hopefully, nothing more that one level would be needed.)
Upon waking up, I realized I got this part of the idea completely wrong. Within
the right side of a #dup, there is only one counter, so numbers wouldn’t be
necessary after the “$$”.
However, we could use numbers to replace the triple-, quadruple-, etc.
dollar-sign idea. So “$$0” is the counter for the current #dup, “$$1” is the
counter for the immediately surrounding #dup, and higher numbers go for outer
layers. Upon expansion, “$$0” goes to the index number of the comma-separated
entity, while “$$n” goes to “$$(n - 1)”. It’s an error to still have
double-dollar symbols remaining after the outermost #dup is expanded.
Oh, the right side of the #dup can take a type, an expression, or a
comma-separated list of one of those.
Here’s an example using theoretical fixed-size arrays:
let tupleOf12 = ( (2, 3, 5, 7), (4, 6, 8, 9), (10, 11, 12, 1) )
let arrayOf12 = { 3, 4 ; #dup(3; #dup(4; tupleOf12 . $$1 . $$0 ) ) }
assert( tupleOf12.0.0 == arrayOf12[0, 0] ) // 2
//…
assert( tupleOf12.2.3 == arrayOf12[2, 3] ) // 1
So resolving the inner #dup gives:
#dup(3; tupleOf12 . $$0 . 0, tupleOf12 . $$0 . 1, tupleOf12 . $$0 . 2,
tupleOf12 . $$0 . 3 )
And doing the remaining #dup gives:
tupleOf12 . 0 . 0, tupleOf12 . 0 . 1, tupleOf12 . 0 . 2, tupleOf12 . 0 . 3,
tupleOf12 . 1 . 0, tupleOf12 . 1 . 1, tupleOf12 . 1 . 2, tupleOf12 . 1 . 3,
tupleOf12 . 2. 0, tupleOf12 . 2 . 1, tupleOf12 . 2 . 2, tupleOf12 . 2 . 3
—
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com
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