Factor implementation of merge assignment

Merge.factor

! With local bindings (7 loc)

: merge ( x y z -- z )
  [| a b c | a b c a length 0 > b length 0 > and ]
  [| a b c | a b c 0 a nth 0 b nth over over < 
    [| a b c x y | 0 a remove-nth b c x over push ]
    [| a b c x y | a 0 b remove-nth c y over push ] if ] 
  while
  [| a b c | a b c b length 0 = [| a b c | c a append ] [| a b c | c b append ] if ] call ;

! Without local bindings (7 loc)

: merge ( x y z -- z )
   [ 2over length 0 > swap length 0 > and ] 
   [ 2over 0 swap nth swap 0 swap nth swap over over < 
     [ 2over swap push drop drop swapd swap 0 swap remove-nth swap swapd ]  
     [ swap 2over swap push drop drop swap swapd 0 swap remove-nth swapd swap ] if ] 
   while 
   swap dup length 0 = [ drop swap append ] [ append nip ] if ;

! Test

--- Data Stack:
V{ 1 3 5 7 9 }
V{ 2 4 6 }
V{ }

(scratchpad) : merge

--- Data Stack:
V{ 1 2 3 4 5 6 7 9 }