Add syntax for global variables

[doug-q]

I would like to write a guppy program such as:

@guppy.global(float)
rot = 1.0

@guppy
main() -> float:
  return rot

which compiles to a hugr containing a global Const node representing rot, which would be some CustomConst including a symbol name and a type. This Const would be further lowered to an extern symbol during codegen.

The syntax used above is purely for explanation and I have no attachment to it.

[ss2165]

does this do the job? (it works now I believe)

rot = 1.0

@guppy
main() -> float:
  return py(rot)

[doug-q]

does this do the job? (it works now I believe)

No it doesn't, although I accept this is a problem with my example. Perhaps It would be clearer to write rot = guppy.GlobalSymbol("rot"). The point is that I need this to compile to an external symbol. Your example will paste "1.0" wherever py(rot) is written.

[ss2165]

yes 👍
for compilation target, does this do the job: CQCL/hugr#233

[qartik]

I think it might be easier to share intent if we replace "global" with "extern"/
"external", e.g., ExternSymbol.

[doug-q]

CQCL/hugr#1123 Adds a CustomConst intended to be used here.