gearsco.de
A chess library for Gleam
Generate promotion moves
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-3
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src/starfish/internal/board.gleam
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src/starfish/internal/board.gleam
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src/starfish/internal/move.gleam
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-3
src/starfish/internal/move.gleam
···
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position: Int,
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moves: List(Move(Legal)),
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) -> List(Move(Legal)) {
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let #(forward, left, right) = case game.to_move {
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board.Black -> #(direction.down, direction.down_left, direction.down_right)
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board.White -> #(direction.up, direction.up_left, direction.up_right)
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let #(forward, left, right, promotion_rank) = case game.to_move {
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board.Black -> #(
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direction.down,
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direction.down_left,
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direction.down_right,
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0,
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)
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board.White -> #(direction.up, direction.up_left, direction.up_right, 7)
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}
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let forward_one = direction.in_direction(position, forward)
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// If moving forward on square is a promotion, then captured are also
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// promotions, because they must move to the same rank. A double-move can
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// never be a promotion because a pawn cannot double move from a position that
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// ends on the promotion rank.
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let is_promotion = board.rank(forward_one) == promotion_rank
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let moves = case iv.get(game.board, forward_one) {
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Ok(board.Empty) -> {
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let moves = case
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can_move(position, forward_one, game.attack_information)
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{
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False -> moves
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True if is_promotion ->
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add_promotions(position, forward_one, moves, board.pawn_promotions)
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True -> [Move(from: position, to: forward_one), ..moves]
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}
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···
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Ok(board.Occupied(colour:, ..)) if colour != game.to_move ->
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case can_move(position, new_position, game.attack_information) {
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False -> moves
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True if is_promotion ->
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add_promotions(position, new_position, moves, board.pawn_promotions)
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True -> [Capture(from: position, to: new_position), ..moves]
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}
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Ok(board.Empty) if game.en_passant_square == Some(new_position) ->
···
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Ok(board.Occupied(colour:, ..)) if colour != game.to_move ->
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case can_move(position, new_position, game.attack_information) {
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False -> moves
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True if is_promotion ->
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add_promotions(position, new_position, moves, board.pawn_promotions)
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True -> [Capture(from: position, to: new_position), ..moves]
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}
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Ok(board.Empty) if game.en_passant_square == Some(new_position) ->
···
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True -> [EnPassant(from: position, to: new_position), ..moves]
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}
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Ok(board.Empty) | Ok(board.Occupied(_, _)) | Error(_) -> moves
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}
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}
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fn add_promotions(
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from: Int,
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to: Int,
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moves: List(Move(Legal)),
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pieces: List(board.Piece),
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) -> List(Move(Legal)) {
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case pieces {
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[] -> moves
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[piece, ..pieces] ->
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add_promotions(from, to, [Promotion(from:, to:, piece:), ..moves], pieces)
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}
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}
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