We already have `{.gcsafe.}`, and `{.noSideEffect.}` blocks and you can tag
functions as `{.sideeffect.}`. Why stay at Rust level when you can go full
blown Haskell?
Example C imported function tagged as side-effect:
<https://github.com/status-im/nim-blscurve/blob/ab07ea0/blscurve/miracl/milagro.nim#L298>
proc FP2_BLS12381_output*(x: ptr FP2_BLS12381) {.sideeffect, milagro_func.}
Run
And example `{.noSideEffect.}` block for benchmarking:
<https://github.com/status-im/nimbus-eth2/blob/9174132/nbench/bench_lab.nim#L66-L74>
template fnEntry(name: string, id: int, startTime, startCycle: untyped):
untyped =
## Bench tracing to insert on function entry
{.noSideEffect, gcsafe.}:
discard BenchMetrics[id].numCalls.atomicInc()
let startTime = getMonoTime()
when SupportsGetTicks:
let startCycle = getTicks()
else:
let startCycle = 0
Run
