! empty, white-... etc are all inlined word which only push an integer on the stack : (initialize-chess-board) 64 empty { ! white pieces [ 0 white-rook spin ] [ 1 white-knight spin ] [ 2 white-bishop spin ] [ 3 white-queen spin ] [ 4 white-king spin ] [ 5 white-bishop spin ] [ 6 white-knight spin ] [ 7 white-rook spin ] [ 8 white-pawn spin ] [ 9 white-pawn spin ] [ 10 white-pawn spin ] [ 11 white-pawn spin ] [ 12 white-pawn spin ] [ 13 white-pawn spin ] [ 14 white-pawn spin ] [ 15 white-pawn spin ] ! black pieces [ 48 black-pawn spin ] [ 49 black-pawn spin ] [ 50 black-pawn spin ] [ 51 black-pawn spin ] [ 52 black-pawn spin ] [ 53 black-pawn spin ] [ 54 black-pawn spin ] [ 55 black-pawn spin ] [ 56 black-rook spin ] [ 57 black-knight spin ] [ 58 black-bishop spin ] [ 59 black-queen spin ] [ 60 black-king spin ] [ 61 black-bishop spin ] [ 62 black-knight spin ] [ 63 black-rook spin ] } [ set-array-nth ] each ;