\r
MACRO: firstn ( n -- )\r
dup zero? [ drop [ drop ] ] [\r
- [ [ '[ , _ nth-unsafe ] ] map ]\r
- [ 1- '[ , _ bounds-check 2drop ] ]\r
+ [ [ '[ [ , ] dip nth-unsafe ] ] map ]\r
+ [ 1- '[ [ , ] dip bounds-check 2drop ] ]\r
bi prefix '[ , cleave ]\r
] if ;\r
\r