type

The type filter takes one argument, a set filter. It returns a number that represents the type of the piece on that square:

  x=type a1
  y=type h1
  x==y

If its argument set filter does not represent a set that has exactly one element, the type filter does not match the position. Otherwise, suppose s is the square represented by the argument set filter. The numeric values of the piece types are given by the following table:

Piece type	Value
empty	0
pawn	1
knight	2
bishop	3
rook	4
queen	5
king	6