Learning Exercise
In Common Lisp like other languages an array is a set of elements which are accessed via integral indexes. The types of the elements can be heterogeneous. The array can be multi-dimensional (not simply 1-dimensional).
make-array allows one to create arrays.
It has many options but its simpler forms allow one to create N-dimensional arrays with all elements initialized to a single value or the array initialized to the values in another sequence (such as a list).
Its first argument is a list of the size of each dimension.
(make-array '(4) :initial-element 3) ; => #(3 3 3 3)
(make-array '(2 2) :initial-element 'x) ; => #2A((X X) (X X))
(Notice how the N-dimensional arrays are printed with the number of dimensions.)
Arrays can also be created by using the same format they are printed in:
#(x y z) ; => #(X Y Z)
#2A((1 2) (3 4)) ; => #2A((1 2) (3 4))
To access elements of a vector use aref, the indexes are zero-based.
The number of indexes provided must match the rank of the array.
(aref #2A((1 2 3) (3 4 5))
1 0) ; => 3
(aref #3A(((a b) (c d))
((e f) (g h))
((t u) (v w)))
2 0 1) ; => U
(aref #2A((1) (2)) 0) ; => ERROR (because not enough indexes provided)
Larry is a Lisp Alien that likes to write code to play games. Today they want to write a few functions to help them with a game which is a lot like tic-tac-toe.
Like tic-tac-toe this game is played on a board which is a 3x3 grid.
First Larry needs a function to make a blank board make-empty-board
All the cells of the board should be NIL.
(make-empty-board) ; => #2A((NIL NIL NIL) (NIL NIL NIL) (NIL NIL NIL))
Next Larry needs a function to make a board from a list of rows. For example:
(make-board-from-list '((A B C) (D E F) (G H I))) ; => #2A((A B C) (D E F) (G H I))
If there is a case where there are 3 of the same symbol in a row then that player has won.
Larry will need a function, all-the-same-p, which given an array of 3 items will evaluate to T if all the items are the same symbol.
(eq can be used to determine if two symbols are the same.)
(all-the-same-p #(A A A)) ; => T
(all-the-same-p #(A B C)) ; => NIL
Now Larry needs a way to get the elements of a row.
The function row will take a board and a row number and should return an array of the elements in that row.
(row #2A((1 2 3) (4 5 6) (7 8 9)) 1) ; => #(4 5 6)
Finally Larry needs a way to get the elements of a column.
The function column will take a board and a column number and should return an array of the elements in that column.
(column #2A((1 2 3) (4 5 6) (7 8 9)) 1) ; => #(2 5 8)
Edit via GitHub
Sign up to Exercism to learn and master Common Lisp with 27 concepts, 83 exercises, and real human mentoring, all for free.