239
Code:

function s($a)
dim $,$i,$c,$n,$t
$=' '
for $n = -$a+1 to 0
$ = Wa + $ + aB
next
$ = split($,a)
$t=join($,'')

for $i = 1 to $a*2
$n=-$n
for $c=$n*($i-2*($i-$a)*($i>$a))*($i<$a*2) to -$c step -2*$n
$[ascan($,' ')] = $[$c+$a]
$[$c+$a]=' '
$t=$t+a+join($,'')
$s=split($t,a)
endfunction