Proposal: replace @parameter with comptime statement modifier

[denis (Denis Gurchenkov)]

@owenhilyard

if comptime (simd_width_of[Float32]() == 1): ...
elif comptime (simd_width_of[Float32]() >= 8): ...
elif parallelism_level() >= 128: ...
else: ..

This already works. The comptime works as a function, so the first and the second conditions are evaluated at comptime, and as you said, the optimizer folds the IFs away.

However, if one did this (under the current proposal)

@owenhilyard

comptime if (simd_width_of[Float32]() == 1): ...
elif (simd_width_of[Float32]() >= 8): ...
elif parallelism_level() >= 128: ... # fails to compile: dynamic condition at comptime
else: ..

The last condition would error out.

I’m of two minds about this. It can be a powerful thing to mix runtime and comptime in one chain, but it also increases the chances of accidental errors, and the workaround is reasonably easy.