chess960 in OCaml — The Rules

Fischer Random Chess (also called Chess960, Chess 960, Fischerandom chess, FR chess, or FullChess) is a chess variant created by Grandmaster Bobby Fischer (the World Champion of chess from 1972 until 1975). It was originally announced on June 19, 1996, in Buenos Aires, Argentina. Fischer's goal was to create a chess variant in which chess creativity and talent would be more important than memorization and analysis of opening moves. His approach was to create a randomized initial chess position, which would thus make memorizing chess opening move sequences far less helpful.

The starting position for Fischer random chess must meet the following rules:

• White pawns are placed on their orthodox home squares.
• All remaining white pieces are placed on the first rank.
• The white king is placed somewhere between the two white rooks.
• The white bishops are placed on opposite-colored squares.
• The black pieces are placed equal-and-opposite to the white pieces. For example, if white's king is placed on b1, then black's king is placed on b8.
• Note that the king never starts on file a or h, because there has to be room for a rook.