Concatenation of seq and array?

[shirleyquirk]

It might be easy to dismiss this as a straw man, with the spurious creation of 
`@[i]` every loop but there's a more realistic gotcha here.

between 
    
    
    for i in 1..1e5:
      result &= i
    
    
    Run

and 
    
    
    for i in 1e5:
      result = result & i
    
    
    Run

The first appends to result, and is fast, the second performs many allocations 
and is slow.

I suppose the second could be auto optimized into the first, maybe even with a 
term rewriting macro but I smell edge cases here I don't know