are nim exceptions "zero cost" (on error-free execution) ? (if so, `defer` should be used more)

[timothee]

> Does defer still have the utterly counterintuitive behavior that it gets 
> called if a statement before it raises an exception?

no, this was debunked, see <https://forum.nim-lang.org/t/4022#25088>, as you 
can also see here: 
    
    
    when true:
      # prints a1 then raises foo
      block:
        echo "a1"
        raise newException(ValueError, "foo")
        echo "a2"
        defer: echo "a3"
        echo "a4"
    
    
    Run