The legal-move? function has the purpose of determining whether or
not a move is legal. This function needs to know the current game
state (which includes the currently selected piece) and the position
where the player is considering moving that piece.
legal-move? : Game Posn -> BooleanThis function is complex, so we break it up into many smaller, simpler functions.
on-board? : Posn -> Boolean: True if the position is on the
board.direction-ok? : Piece Posn -> Boolean: This function just makes
sure that ordinary pieces only move the direction they start.space-empty?: (Listof Piece) Posn -> Boolean: Is the given square
empty?distance-nonjump-ok?: Posn Posn -> Boolean: Assuming the move is
not a jump, is it ok?distance-jump-ok?: Posn Posn -> Boolean: Assuming the move is a
jump, is the distance intended going to be ok?get-piece: (Listof Piece) Posn -> Piece: Get the piece at the
given position. Define a fake NO-PIECE to be a piece at (-1000,1000)
to represent not finding a piece there.is-legal-to-jump?: (Listof Piece) Player Posn Posn -> Boolean:
Knowing where the pieces are on the board and who is attempting the
move, is the attempted jump legal? For example, jumping an opponent
is ok, but jumping your own piece or an empty square is
forbidden. Plan to figure out some helper functions for this on your own!Each function needs several check-expects before you start to write the function. Do not start to write a function without a purpose and at least two checks.
On board just makes sure the position is on the board… My board squares are numbered 0 through 7.
(check-expect (on-board? (make-posn -10 5)) false)
(check-expect (on-board? (make-posn 2 7)) true)
(check-expect (on-board? (make-posn 3 8)) false)We need to write check-expects for direction. First, we need to decide which direction each player will move. I decided that player 1 will move down the board (increasing y) and player 2 will move up (decreasing y).
The possibilities are:
(check-expect (direction-ok? (make-piece (make-posn 1 3) 1 false)
(make-posn 1 2))
false)
(check-expect (direction-ok? (make-piece (make-posn 1 3) 1 false)
(make-posn 2 4))
true)
(check-expect (direction-ok? (make-piece (make-posn 1 3) 2 false)
(make-posn 2 4))
false)
(check-expect (direction-ok? (make-piece (make-posn 1 3) 2 false)
(make-posn 0 2))
true)
(check-expect (direction-ok? (make-piece (make-posn 1 3) 2 true)
(make-posn 2 4))
true)
(check-expect (direction-ok? (make-piece (make-posn 1 3) 1 true)
(make-posn 0 4))
true)The space-empty? function should find out if a space is empty.
(define ex-pieces (list (make-piece (make-posn 1 3) 1 true)
(make-piece (make-posn 2 4) 2 false)
(make-piece (make-posn 3 5) 1 false)))
(check-expect (space-empty? ex-pieces (make-posn 1 3))
false)
(check-expect (space-empty? ex-pieces (make-posn 3 1))
true)
(check-expect (space-empty? ex-pieces (make-posn 2 4))
false)
(check-expect (space-empty? ex-pieces (make-posn 3 5))
false)The distance-nonjump-ok? function takes two positions and determines
if the distance between them is allowed given that the move is not a
jump.
(check-expect (distance-nonjump-ok? (make-posn 1 3)
(make-posn 2 4))
true)
(check-expect (distance-nonjump-ok? (make-posn 1 3)
(make-posn 0 4))
true)
(check-expect (distance-nonjump-ok? (make-posn 1 3)
(make-posn 2 2))
true)
(check-expect (distance-nonjump-ok? (make-posn 1 3)
(make-posn 0 2))
true)
(check-expect (distance-nonjump-ok? (make-posn 1 3)
(make-posn 1 4))
false)
(check-expect (distance-nonjump-ok? (make-posn 1 3)
(make-posn 2 3))
false)The distance-jump-ok? function returns true when the two positions
differ by enough that there is exactly one diagonal square between
them.
You should write your own checks for this function.
The is-legal-to-jump? determines if the square that is being jumped
over is occupied by the correct kind of piece.