I'm trying to define a type for Boolean simple-arrays. This should be easy enough:
(deftype boolean-vector (&optional (length '*))
"Simple vector of BOOLEAN elements."
`(simple-array boolean (,length)))
yet:
CL-USER> (typep #(nil nil t t t) 'boolean-vector)
T
CL-USER> (typep #(nil nil t t 5) 'boolean-vector)
T
CL-USER> (typep 5 'boolean)
NIL
Anyone have any ideas why this deftype isn't doing what it's supposed to and how to properly define a vector type that contains only elements of type boolean?
Answer
Two good explanations appear below. What I ended up doing:
(defun boolean? (object)
"Check type of OBJECT is BOOLEAN."
(typep object 'boolean))
(defun boolean-sequence-p (x)
(every #'boolean? x))
(deftype simple-boolean-vector (&optional (length '*))
"Vector of BOOLEAN elements."
`(and (simple-array * (,length))
(satisfies boolean-sequence-p)))
deftype is doing what it is supposed to do, but
> (upgraded-array-element-type 'boolean)
t
In other words there is no specialised array type which can hold only t and nil: you can't have an array which can hold only booleans in your implementation. Of course it is possible that an implementation could support such a thing but I think it would be extraordinarily unlikely.
If you want an array type which can hold only true or false values then you probably want bit-vectors which are required to exist, with some wrappers. For instance:
(deftype array-index ()
`(integer 0 (,array-dimension-limit)))
(defun make-boolean-vector (n &key (initial-element nil))
(declare (type array-index n)
(type boolean initial-element))
(make-array (list n) :element-type 'bit :initial-element (if initial-element 1 0)))
(declaim (inline bref (setf bref)))
(defun bref (v n)
(declare (type bit-vector v)
(type array-index n))
(= (bit v n) 1 t nil))
(defun (setf bref) (b v n)
(declare (type bit-vector v)
(type array-index n)
(type boolean b))
(setf (bit v n) (if b 1 0))
b)
Try this:
(defun bool-array (a)
(and (simple-array-p a)
(every (lambda (e) (typep e 'boolean)) a)))
(deftype boolean-vector ()
`(satisfies bool-array))
Test:
> (typep #(nil nil t t t) 'boolean-vector)
T
> (typep #(nil nil t t 5) 'boolean-vector)
NIL
> (typep 5 'boolean-vector)
NIL
Related
I'm trying to do a recursive version of the function position called positionRec. The objective is define the position of an element in a list, and if the element is not in the list return "nil". For exemple:
(positionRec 'a '(b c d a e)) => 4
(positionRec 'a '(b c d e)) => nil
I have written:
(defun positionRec (c l)
(cond
((atom l) (return nil))
((equal c (first l)) 1)
(t (+ 1 (positionRec c (rest l)))) ) )
I don't succeed to return nil. I have an error "*** - return-from: no block named nil is currently visible"
Anyone can teach me how to do it?
Lisp is an expression language: it has only expressions an no statemends. This means that the value of a call to a function is simply the value of the last form involved in that call This is different than many languages which have both statements and expressions and where you have to explicitly litter your code with explicit returns to say what the value of a function call is.
A cond form in turn is an expression. The value of an expression like
(cond
(<test1> <test1-form1> ... <test1-formn>)
(<test2> <test1-form1> ... <test1-formn>)
...
(<testn> <testn-form1> ... <testn-formnn>))
is the <testm-formn> of the first <testm> which is true, or nil if none of them are (and as a special case, if there are no forms after a test which is true the value is the value of that test).
So in your code you just need to make sure that the last form in the test which succeeds is the value you want:
(defun positionRec (c l)
(cond
((atom l) nil)
((equal c (first l)) 1)
(t (+ 1 (positionRec c (rest l))))))
So, what use is return? Well, sometimes you really do want to say 'OK, in the middle of some complicated loop or something, and I'm done now':
(defun complicated-search (...)
(dolist (...)
(dolist (...)
(dotimes (...)
(when <found-the-interesting-thing>
(return-from complicated-search ...))))))
return itself is simply equivalent to (return-from nil ...) and various constructs wrap blocks named nil around their bodies. Two such, in fact, are dotimes and dolist, so if you want to escape from a big loop early you can do that:
(defun complicated-search (...)
(dolist (...)
(when ...
(return 3)))) ;same as (return-from nil 3)
But in general because Lisp is an expression language you need to use return / return-from much less often than you do in some other languages.
In your case, the modified function is going to fail: if you get to the ((atom l) nil) case, then it will return nil to its parent which will ... try to add 1 to that. A better approach is to keep count of where you are:
(defun position-of (c l)
(position-of-loop c l 1))
(defun position-of-loop (c l p)
(cond
((atom l) nil)
((equal c (first l)) p)
(t (position-of-loop c (rest l) (1+ p)))))
Note that this (as your original) uses 1-based indexing: zero-based would be more compatible with the rest of CL.
It would probably be idiomatic to make position-of-loop a local function:
(defun position-of (c l)
(labels ((position-of-loop (lt p)
(cond
((atom lt) nil)
((equal c (first lt)) p)
(t (position-of-loop (rest lt) (1+ p))))))
(position-of-loop l 1)))
And you could then use an iteration macro if you wanted to make it a bit more concise:
(defun position-of (c l)
(iterate position-of-loop ((lt l) (p 1))
(cond
((atom lt) nil)
((equal c (first lt)) p)
(t (position-of-loop (rest lt) (1+ p))))))
The main problem is that you're trying to deal with incommensurable values. On the one hand, you want to deak with numbers, on the other, you want to deal with the empty list. You cannot add a number to a list, but you will inherently try doing so (you have an unconditional (1+ ...) call in your default branch in your cond).
There are ways to work around that, one being to capture the value:
(cond
...
(t (let ((val (positionRec c (rest l))))
(when val ;; Here we "pun" on nil being both false and the "not found" value
(1+ val)))))
Another would be to use a method amenable to tail-recursion:
(defun positionrec (element list &optional (pos 1))
(cond ((null list) nil)
((eql element (head list)) pos)
(t (positionrec element (rest list) (1+ pos)))))
The second function can (with a sufficently smart compiler) be turned into, basically, a loop. The way it works is by passing the return value as an optional parameter.
You could build a version using return, but you would probably need to make use of labels for that to be straight-forward (if you return nil directly from the function, it still ends up in the (1+ ...), where you then have numerical incompatibility) so I would go with either "explicitly capture the value and do the comparison against nil/false" or "the version amenable to tail-call elimination" and simply pick the one you find the most readable.
I want to get a function argument value, using an argument name.
The following code don't works, because symbol-value working only with global variables:
(defun test1 (&key v1)
(format t "V1: ~A~%" (symbol-value (intern "V1"))))
Is there a portable way to do this in Common Lisp?
You can use a custom environment to map strings to functions:
(use-package :alexandria)
(defvar *env* nil)
(defun resolve (name &optional (env *env*))
(if-let (entry (assoc name env :test #'string=))
(cdr entry)
(error "~s not found in ~a" name env)))
(defmacro bind (bindings env &body body)
(assert (symbolp env))
(let ((env (or env '*env*)))
(loop
for (n v) in bindings
collect `(cons ,n ,v) into fresh-list
finally
(return
`(let ((,env (list* ,#fresh-list ,env)))
,#body)))))
(defmacro call (name &rest args)
`(funcall (resolve ,name) ,#args))
For example:
(bind (("a" (lambda (u) (+ 3 u)))
("b" (lambda (v) (* 5 v))))
nil
(call "a" (call "b" 10)))
Here is another version of an explicit named-binding hack. Note this isn't well (or at all) tested, and also note the performance is not going to be great.
(defun named-binding (n)
;; Get a binding by its name: this is an error outside
;; WITH-NAMED-BINDINGS
(declare (ignore n))
(error "out of scope"))
(defun (setf named-binding) (val n)
;; Set a binding by its name: this is an error outside
;; WITH-NAMED-BINDINGS
(declare (ignore val n))
(error "out of scope"))
(defmacro with-named-bindings ((&rest bindings) &body decls/forms)
;; establish a bunch of bindings (as LET) but allow access to them
;; by name
(let ((varnames (mapcar (lambda (b)
(cond
((symbolp b) b)
((and (consp b)
(= (length b) 2)
(symbolp (car b)))
(car b))
(t (error "bad binding ~S" b))))
bindings))
(decls (loop for df in decls/forms
while (and (consp df) (eql (car df) 'declare))
collect df))
(forms (loop for dft on decls/forms
for df = (first dft)
while (and (consp df) (eql (car df) 'declare))
finally (return dft)))
(btabn (make-symbol "BTAB")))
`(let (,#bindings)
,#decls
(let ((,btabn (list
,#(mapcar (lambda (v)
`(cons ',v (lambda (&optional (val nil valp))
(if valp
(setf ,v val)
,v))))
varnames))))
(flet ((named-binding (name)
(let ((found (assoc name ,btabn)))
(unless found
(error "no binding ~S" name))
(funcall (cdr found))))
((setf named-binding) (val name)
(let ((found (assoc name ,btabn)))
(unless found
(error "no binding ~S" name))
(funcall (cdr found) val))))
(declare (inline named-binding (setf named-binding)))
,#forms)))))
And now:
> (with-named-bindings ((x 1))
(setf (named-binding 'x) 2)
(named-binding 'x))
2
Even better:
(defun amusing (x y)
(with-named-bindings ((x x) (y y))
(values #'named-binding #'(setf named-binding))))
(multiple-value-bind (reader writer) (amusing 1 2)
(funcall writer 2 'x)
(funcall reader 'x))
will work.
I am trying to make a 'pseudo OO system':
(defun bank-account ()
(let ((balance))
(labels ((init (x)
(setf balance x))
(increment (x)
(setf balance (+ balance x)))
(get-balance ()
balance))
(lambda (func)
(case func (init #'init)
(increment #'increment)
(get-balance #'get-balance))))))
(defparameter bank-account-object (bank-account))
(funcall (funcall bank-account-object 'init) 42)
(funcall (funcall bank-account-object 'increment) 10)
(funcall (funcall bank-account-object 'get-balance))
Q: are there better ways to accomplish the same without using CLOS, defstruct, or defmacro?
The problem that I see with this is that it is closed for extension, and I see no simple way to add extensibility.
Minor nitpick: that's not a bank-system but a bank-account. When you think about that further, it seems to me that the interesting part about this example domain has not been touched: double accounting, i. e. ensuring the null-sum invariant.
There are two sayings: a closure is a poor man's object, and an object is a poor man's closure. I have the feeling that you are more in the realm of the former here. However, it might be a good learning experience to think about this—as long as you don't put it into production somewhere…
;; The "class"
(defun create-bank-account ()
(let ((balance))
(labels ((init (x)
(setf balance x))
(increment (x)
(setf balance (+ balance x)))
(get-balance ()
balance))
(lambda (func)
(case func (init #'init)
(increment #'increment)
(get-balance #'get-balance))))))
;; The "methods"
(defun init-balance (object amount)
(funcall (funcall object 'init) amount))
(defun increment-balance (object amount)
(funcall (funcall object 'increment) amount))
(defun get-balance (object)
(funcall (funcall object 'get-balance)))
;; Example usage
(defparameter bank-account (create-bank-account))
(init-balance bank-account 42) ; => 42
(increment-balance bank-account 10) ; => 52
(get-balance bank-account) ; => 52
As mentioned in other answers, the resulting object might be hard to extend. That could be a feature, but one possible way to improve on it is to let it be redefined dynamically. You can even switch from classes to protoypes.
(ql:quickload :optima)
(defpackage :obj (:use :cl :optima))
(in-package :obj)
(defun make-object (&optional prototype)
(let ((properties (make-hash-table :test #'eq))
(self))
(flet ((resolve (key)
(or (gethash key properties)
(and prototype (funcall prototype :get key)))))
(setf self
(lambda (&rest args)
(optima:ematch args
((list :get :prototype) prototype)
((list :get key) (resolve key))
((list :set :prototype p)
(cerror "Continue" "Changing prototype object, are you sure?")
(setf prototype p))
((list :set key value)
(if value
(setf (gethash key properties) value)
(remhash key properties)))
((list :invoke method args)
(let ((resolved (resolve method)))
(if resolved
(apply resolved self args)
(funcall (or (resolve :no-such-method)
(error "No such method: ~a in ~a"
method
self))
self
method))))))))))
Some helper symbols:
;; call built-in command
(defmacro $ (obj method &rest args)
`(funcall ,obj ,method ,#args))
;; access property
(declaim (inline # (setf #)))
(defun # (o k) ($ o :get k))
(defun (setf #) (v o k) ($ o :set k v))
;; invoke method
(defun % (o m &rest a)
($ o :invoke m a))
A simple test
(let ((a (make-object)))
;; set name property
(setf (# a :name) "a")
;; inherit
(let ((b (make-object a)))
(print (list (# b :name)
;; shadow name property
(setf (# b :name) "b")
(# a :name)))
;; define a method
(setf (# a :foo) (lambda (self) (print "FOO")))
;; invoke it
(% a :foo)))
Bank account
(defun create-bank-account (&optional parent)
(let ((account (make-object parent)))
(prog1 account
(setf (# account :init)
(lambda (self x)
(setf (# self :balance) x)))
(setf (# account :increment)
(lambda (self increment)
(incf (# self :balance) increment))))))
(let ((account (create-bank-account)))
(% account :init 0)
(% account :increment 100)
(# account :balance))
100
I'm trying to make a Mancala game in Lisp. It's going to have an AI to play against a human player, but I'm stuck. I can't find the way to represent the board as list; the major issue in my mind is how to move the tokens. Here are the references of how to play mancala
I'm thinking about a circular list, but I can't find any clear documentation on how to do that in Lisp.
Sorry about my grammar; English is not my native language.
Now I havent read the rules (sorry!) so this is just to address the idea of using a circular data structure.
A data structure doesnt have to be circular. As long as you pretend it is it will work!
Have a read of the mod function.
;; a1 a6 b1 b6
(defparameter *board* '(nil nil nil nil nil nil nil nil nil nil nil nil))
(defun wrap-position (pos)
(mod pos (length *board*)))
(defun push-token (position)
(push t (nth (wrap-position position) *board*)))
(defun pull-token (position)
(let ((contents (nth (wrap-position position) *board*)))
(setf (nth (wrap-position position) *board*) (rest contents))))
(defun print-board ()
(format t "| ~{~10<~a~>~} |~%| ~{~10<~a~>~} |" (reverse (subseq *board* 6))
(subseq *board* 0 6))
*board*)
Now the technique above is destructive. If you don't know yet what that is in lisp have a google or search here on stackoveflow, there are some good descriptions. It is worth looking into as you may find that your AI want to 'try out' lots of potential moves with 'damaging' the actual game board, a non destructive approach can help with this. The phenomenal book land of lisp has some great info on this.
Here is a simple usage example
CL-USER> *board*
(NIL NIL NIL NIL NIL NIL NIL NIL NIL NIL NIL NIL)
CL-USER> (push-token 5)
(T)
CL-USER> *board*
(NIL NIL NIL NIL NIL (T) NIL NIL NIL NIL NIL NIL)
CL-USER> (push-token 5)
(T T)
CL-USER> *board*
(NIL NIL NIL NIL NIL (T T) NIL NIL NIL NIL NIL NIL)
CL-USER> (PULL-token 5)
(T)
CL-USER> *board*
(NIL NIL NIL NIL NIL (T) NIL NIL NIL NIL NIL NIL)
...I change the board before doing the next bit...
CL-USER> (print-board)
| NIL NIL NIL NIL NIL NIL |
| NIL NIL NIL NIL NIL (T T T T) |
Now have a look at Sylwester's answer and see that you can replace the sublists with just a number of stones. You will need to change the print-board obviously but that gives you a very simple model you can manipulate very easily (almost can be the big step you need to make this non-destructive). Have a go!
I would have used an array of 14 fixnums. index 0-5 are pits for A, 6 is A's basket. 7-12 are pits for player B and 13 is B's basket. You do minimax with copy-array.
If you want lists I would have either had A and B's lists individually or interleaved them. You could also just have a list of 14 cons.
Sorry, I couldn't really understand how to play the game, but here's something I could think about w/r to how to go about the board:
(defstruct (mancala-cell
(:print-object
(lambda (cell stream)
(format stream "<stones: ~d>"
(length (mancala-cell-stones cell))))))
(stones nil :type list)
(next nil))
(defun make-cells ()
(labels ((%make-cells (head count)
(let ((next (make-mancala-cell)))
(setf (mancala-cell-next head) next)
(if (> count 0) (%make-cells next (1- count)) next))))
(let* ((first (make-mancala-cell))
(last (%make-cells first 12)))
(setf (mancala-cell-next last) first))))
(defstruct (mancala-board
(:print-object
(lambda (board stream)
(loop :for i :from 0 :below 12
:for cell := (mancala-board-cells board)
:then (mancala-cell-next cell)
:do (princ (case i
(6 #\Newline) (0 "") (otherwise #\-))
stream)
(princ cell stream)))))
(cells (make-cells) :type mancala-cell))
(print (make-mancala-board))
;; <stones: 0>-<stones: 0>-<stones: 0>-<stones: 0>-<stones: 0>-<stones: 0>
;; <stones: 0>-<stones: 0>-<stones: 0>-<stones: 0>-<stones: 0>-<stones: 0>
Then here's one more example:
(defstruct (mancala-cell
(:print-object
(lambda (cell stream)
(format stream "<stones: ~d>"
(mancala-cell-stones cell)))))
(stones 4 :type fixnum))
(defconstant +null-cell+ (make-mancala-cell))
(deftype mancala-grid () '(array mancala-cell (12)))
(defun make-cells ()
(loop
:for i :from 0 :below 12
:with result := (make-array
12 :element-type 'mancala-cell
:initial-element +null-cell+)
:do (setf (aref result i) (make-mancala-cell))
:finally (return result)))
(defstruct (mancala-board
(:print-object
(lambda (board stream)
(loop :for i :from 0 :below 12
:for cell :across (mancala-board-cells board)
:do (princ (case i
(6 #\Newline) (0 "") (otherwise #\-))
stream)
(princ cell stream)))))
(cells (make-cells) :type mancala-grid))
(defun map-cells-in-range (function board &key (start 0) (end 12))
(loop
:for i :from start :below end
:with board := (mancala-board-cells board)
:collect (funcall function (aref board (mod i 12)))))
(defun fold-cells-in-range (function board &key (start 0) (end 12))
(loop
:for i :from start :below (1- end)
:with board := (mancala-board-cells board)
:for cell := (aref board (mod i 12))
:for result := (funcall
function
(aref board (mod i 12))
(aref board (mod (1+ i) 12)))
:then (funcall function result (aref board (mod (1+ i) 12)))
:finally (return result)))
(fold-cells-in-range
(lambda (a b)
(+ (mancala-cell-stones b)
(if (integerp a) a (mancala-cell-stones a))))
(make-mancala-board)) ; 48
I am trying to implement a macro which expands a unlimited list of triplet-arguments into lambda-function to check an argument (object).
e.g.
(where >= amount 5 equalp name "george")
=>
#'(lambda (arg)
(and
(>= (amount arg) 5)
(equalp (name arg) "george")))
I got quite close with this macrodefinition:
(defmacro where (&rest list-of-argument-triplets )
`#'(lambda (arg)
(and
,(do ( (counter 0 (+ counter 3)) (liste (list)))
( (>= counter (list-length list.of-argument-triplets)) liste)
(push `( ,(nth counter list-of-argument-triplets)
( ,(nth (+ counter 1) list-of-argument-triplets) arg)
,(nth (+ counter 2) list-of-argument-triplets)
liste)))))
but this expands to
#'(lambda (arg)
(and ((>= (amount arg) 5)
(equalp (name arg) "george"))))
which is one parentheses after the "and" too much. As a conclusion I would have to use an # in front of the result-form, but then the "#list" is treated
as if it is an parameter-name, and therefore I get an no-value error, instead of an expanded list.
*** - RETURN-FROM: variable #LISTE has no value
How can I fix that?
Code smell: you use NTH to access elements of a list.
I would first define a helper function, which makes out of the flat list a list of three element lists:
(defun triplets (list)
(loop while list
collect (list (pop list)
(pop list)
(pop list))))
CL-USER 1 > (triplets '(a b c d e f g h i))
((A B C) (D E F) (G H I))
The macro is then slightly simpler to write:
(defmacro where (&rest flat-triplets)
`#'(lambda (arg)
(and
,#(mapcar (lambda (triplet)
(destructuring-bind (fn accessor item)
triplet
`(,fn (,accessor arg) ,item)))
(triplets flat-triplets))))
CL-USER 2 > (macroexpand-1 '(where >= amount 5 equalp name "george"))
(FUNCTION (LAMBDA (ARG) (AND (>= (AMOUNT ARG) 5) (EQUALP (NAME ARG) "george"))))
T