When nimvm statement

nimvm is a special symbol, that may be used as expression of when nimvm statement to differentiate execution path between compile time and the executable.

Example:

proc someProcThatMayRunInCompileTime(): bool =
  when nimvm:
    # This branch is taken at compile time.
    result = true
  else:
    # This branch is taken in the executable.
    result = false
const ctValue = someProcThatMayRunInCompileTime()
let rtValue = someProcThatMayRunInCompileTime()
assert(ctValue == true)
assert(rtValue == false)

when nimvm statement must meet the following requirements:

• Its expression must always be nimvm. More complex expressions are not allowed.
• It must not contain elif branches.
• It must contain else branch.
• Code in branches must not affect semantics of the code that follows the when nimvm statement. E.g. it must not define symbols that are used in the following code.