Re: optional params before `untyped` body

[timothee]

with this PR 
[https://github.com/nim-lang/Nim/pull/11754](https://github.com/nim-lang/Nim/pull/11754)
 we can do it as follows:
    
    
    dispatch foo:
        for a in 0..<3:
          echo a
        echo 10
    
    
    Run