So using common lisp, I want to be able to do something of the sorts of:
(defmacro foo (count &rest someExpression)
`(do
((,count 0 (+ ,count 1)))
((= ,count 5) T)
`(eval ,someExpression)
)
)
(foo (print 1) temp)
With the result of it printing 1 5 times. I do not want to simply call (print 1) directly, but by passing the expression through a macro parameter and calling it via the macro. In other words, the macro foo should handle any expression(s) as input and run it. This case does not seem to work.
Edited to clarify an explicit script and intended function.
Starting with your recent version, which is at least a reasonable candidate for a macro unlike the older one:
(defmacro foo (someExpression count-var)
`(do ((,count-var 0 (+ ,count 1)))
((= ,count-var 5) T)
`(eval (,someExpression))))
Well what is the expansion of (foo (print 1) c)?
(foo (print 1) x)
-> (do ((x 0 (+ x 1))) ((= x 5) t)
`(eval (,someexpression)))
Well, that's a disaster: what is that nested backquote doing? Let's just remove it:
(defmacro foo (someExpression count-var)
`(do ((,count-var 0 (+ ,count 1)))
((= ,count-var 5) T)
(eval (,someExpression))))
(foo (print 1) x)
-> (do ((x 0 (+ x 1))) ((= x 5) t)
(eval ((print 1))))
That's less disastrous, but the eval form is entirely bogus. We can make that 'work' by changing it to be at least syntactically legal:
(defmacro foo (someExpression count)
`(do ((,count 0 (+ ,count 1)))
((= ,count 5) T)
(eval ,someExpression)))
And now
(foo (print 1) x)
-> (do ((x 0 (+ x 1))) ((= x 5) t)
(eval (print 1)))
And this will 'work' but it will work purely by coincidence: because (print 1) returns 1 and the value of 1 is 1.
(foo (print 'foo) x)
-> (do ((x 0 (+ x 1))) ((= x 5) t)
(eval (print 'foo)))
and that's a run-time error.
But ... why are you using eval? eval is a terrible, terrible solution to almost any problem you can think of, unless the solution to the problem is called 'code injection attack', and in this case it's not just terrible: it's wrong. So we just remove it.
(defmacro foo (someExpression count)
`(do ((,count 0 (+ ,count 1)))
((= ,count 5) T)
,someExpression))
And now
(foo (print 'foo) x)
-> (do ((x 0 (+ x 1))) ((= x 5) t)
(print 'foo))
Which looks like the code transformation we want. So, finally:
> (foo (print 'foo) x)
foo
foo
foo
foo
foo
t
Which is, finally, fine. And this works:
> (foo (print x) x)
0
1
2
3
4
t
As with yet another edit to the question it probably is more useful to put the variable name first and allow a bunch of expressions:
(defmacro foo (count-var &body forms)
`(do ((,count-var 0 (+ ,count-var 1)))
((= ,count-var 5))
,#forms))
This will now allow multiple expressions in the body. And we could go further: we could allow it to specify the number of iterations and the return value`:
(defmacro foo ((count-var &optional (count 1) (value 'nil)) &body forms)
`(do ((,count-var 0 (1+ ,count-var)))
((= ,count-var ,count) ,value)
,#forms))
And now
> (foo (x 2)
(print x)
(print (* x 2)))
0
0
1
2
nil
Well, the name of this macro is dotimes of course.
I am trying to understand Racket's macros. For that, I built this function for a specific purpose:
(define (while-less-fun max)
(cond [(< a (- max 1))
(and (begin (set! a (+ a 1)) (print "x") a) (while-less-fun max))]
[(< a max)
(begin (set! a (+ a 1)) (print "x") a)]
[(>= a max)
(begin (set! a (+ a 1)) (print "x") a)]
))
It works as intended on the REPL:
> a
2
> (while-less-fun 7)
"x""x""x""x""x"7
> a
7
I tried to transform the function above in the macro bellow. My goal would be to generate the same results:
(define-syntax while-less
(syntax-rules (do)
[(while-less maximo do begin-exp)
(cond [(< a (- maximo 1))
(and begin-exp (while-less maximo do begin-exp))]
[(< a maximo)
begin-exp]
[(>= a maximo)
begin-exp])]))
The expected result was:
(define a 2)
(while-less 7 do (begin (set! a (+ a 1)) (print "x") a))
(while-less 7 do (begin (set! a (+ a 1)) (print "x") a))
Evaluating the second line would print "x" 5 times and change a to be 7. Also, evaluating the third line would print "x" 1 time and would change a to be 8.
Unfortunately, this generates an infinite recursion which really surprises me.
What did I do wrong? Why did this infinite recursion happen?
I know that you should avoid writing macros when a function is able to solve the problem. But, is my approach the wrong way of trying to accomplish this task?
In the first cond clause, you call "(while-less maximo do begin-exp)" with the same arguments, the entire body of the macro will be expanded again by calling the same "(while-less maximo do begin-exp)", causing the loop.
What you can do is create a generic while for a condition:
(define-syntax while
(syntax-rules (do)
[(while condition do begin-exp)
(let loop ()
(when condition
begin-exp
(loop)))]))
> (define a 2)
> (while (< a 7) do (begin (set! a (+ a 1)) (print "x") a))
"x""x""x""x""x"
> (while (< a 7) do (begin (set! a (+ a 1)) (print "x") a))
>
I'm quite new to LISP and I am trying to work on the cond statement for class. Currently, I am attempting to check if the value passed is a list and if so, append the letter d onto the list.
Here is my code:
(defun test(L)
(listp L)
(cond ((listp L) (append L (list 'd)))
)
(write L)
)
(test (list 'a 'b 'c))
The output I get is:
(A B C)
(A B C)
If I change the test to: (test (car(list 'a 'b 'c)))
The new output I get is:
A
A
Two things I am wondering is
1.) Why isn't D appended onto the list if the first test passes a list?
2.) Why are they being printed twice? I'm using LISP Works so I figure it's actually something with how it always outputs the final value or something.
1.) The same reason str + "d" doesn't mutate str in Java or Python. It creates a new list that you do not use!
>>> str + "d"
'abcd'
>>> str
'abc'
Crazy similar isn't it?
2.) In CL the return is the last evaluated expression. The REPL prints every top level expression result to the terminal. Python does this too:
>>> def test():
... x = 2 + 3
... print x
... return x
...
>>> test()
5
5
Update
How to mutate the argument list. The simple answer is that you need to mutate the last pair of the argument instead:
(defun test (l)
(assert (consp 1) (l) "l needs to be a non nil list. Got: ~a" l)
(nconc l (list 'd)
(write l)))
(defparameter *test1* (list 1 2 3))
(defparameter *test1-copy* *test1*)
(test *test1*) ; ==> (1 2 3 d) (and prints (1 2 3 d))
*test1* ; ==> (1 2 3 d)
*test1-copy* ; ==> (1 2 3 d)
(eq *test1* *test1-copy*) ; ==> t
(test '())
** error l needs to be a non nil list. Got: NIL
(nconc l x) does (setf (cdr (last l)) x)
If you need to alter the binding, then you need to make a macro:
(defmacro testm (var)
(assert (symbolp var) (var) "List needs to be a variable binding. Got: ~a" var)
`(progn
(when (listp ,var)
(setf ,var (append ,var (list 'd)))
(write ,var))))
(macroexpand '(testm *test2*))
; ==> (progn
; (when (consp *test2*)
; (setf *test2* (append *test2* (list 'd))))
; (write *test2*))
(defparameter *test2* (list 1 2 3))
(defparameter *test2-copy* *test2*)
(testm *test2*) ; ==> (1 2 3 d) (and prints (1 2 3 d))
*test2* ; ==> (1 2 3 d)
*test2-copy* ; ==> (1 2 3)
(eq *test2* *test2-copy*) ; ==> nil
(defparameter *x* nil)
(testm *x*) ; ==> (d) (and prints (d))
*x* ; ==> (d)
(testm '(1))
** error List needs to be a variable binding. Got: '(1)
Idiomatic way to do it
(defun test (list)
(if (consp list)
(append list '(d))
list))
(write (test '(1 2 3)))
; ==> (1 2 3 d) (and prints (1 2 3 d))
(defparameter *test3* '(1 2 3))
(setf *test3* (test *test3*))
*test3* ; ==> (1 2 3 d)
Say I have a macro like this:
(define-syntax (choose stx)
(define data (syntax->datum stx))
(define args (cadr data))
(define body (cddr data))
(define output
`(apply (case (car ,args)
,(map (lambda (choice)
`((,(car choice)) ,(cadr choice)))
body)
(else (displayln "error")))
(cdr ,args)))
(println output)
#'(void))
If I use this on something like this (there could be more options):
(choose args
("run" runsomething)
("del" delsomethingelse))
It transforms it to
(apply
(case (car args)
((("run") runsomething)
(("del") delsomethingelse))
(else (displayln "error")))
(cdr args))
Which is not valid code, because the map gave it extra parentheses. Instead I want it to give me this:
(apply
(case (car args)
(("run") runsomething)
(("del") delsomethingelse)
(else (displayln "error")))
(cdr args))
How could I do something like this?
Use unquote-splicing (aka ,#) to get rid of the list surrounding map.
Example:
(define xs '(a b c))
`(1 2 ,xs 3 4) ; => '(1 2 (a b c) 3 4)
`(1 2 ,#xs 3 4) ; => '(1 2 a b c 3 4)
However I notice that you use syntax->datum on the input stx
of the syntax transformer. That removes lexical information, which
could end up causing problems. It recommend using either syntax-case
or syntax-parse, which use pattern matching to pick out the elements
of the input syntax and templates to generate the output.
(define-syntax (choose stx)
(syntax-case stx ()
[(_choose args
(datum fun-expr)
...)
#'(apply (case (car args)
[(datum) fun-expr]
...)
(cdr args))]))
(define (run-it . xs) (list 'ran-it xs))
(define (del-it . xs) (list 'delt-it xs))
(choose (list "run" 1 2 3)
("run" run-it)
("del" del-it))
Output: '(ran-it (1 2 3))
I'm new to lisp, and have been trying to learn Common Lisp by diving in and writing some code. I've read plenty of documentation on the subject, but it's taking a while to really sink in.
I have written a couple of macros (? and ??) for performing unit tests, but I'm having some difficulty. The code is at the end of the post, to avoid cluttering the actual question.
Here is an example of usage:
(??
(? "Arithmetic tests"
(? "Addition"
(= (+ 1 2) 3)
(= (+ 1 2 3) 6)
(= (+ -1 -3) -4))))
And an example of output:
[Arithmetic tests]
[Addition]
(PASS) '(= (+ 1 2) 3)'
(PASS) '(= (+ 1 2 3) 6)'
(PASS) '(= (+ -1 -3) -4)'
Results: 3 tests passed, 0 tests failed
Now, the existing code works. Unfortunately, the (? ...) macro is ugly, verbose, resistant to change - and I'm pretty sure also badly structured. For example, do I really have to use a list to store pieces of output code and then emit the contents at the end?
I'd like to modify the macro to permit description strings (or symbols) to optionally follow each test, whereupon it would replace the test literal in the output, thus:
(??
(? "Arithmetic tests"
(? "Addition"
(= (+ 1 2) 3) "Adding 1 and 2 results in 3"
(= (+ 1 2 3) 6)
(= (+ -1 -3) -4))))
Output:
[Arithmetic tests]
[Addition]
(PASS) Adding 1 and 2 results in 3
(PASS) '(= (+ 1 2 3) 6)'
(PASS) '(= (+ -1 -3) -4)'
But unfortunately I can't find a sensible place in the macro to insert this change. Depending on where I put it, I get errors like you're not inside a backquote expression, label is not defined or body-forms is not defined. I know what these errors mean, but I can't find a way to avoid them.
Also, I'll be wanting to handle exceptions in the test, and treat that as a failure. Currently, there is no exception handling code - the test result is merely tested against nil. Again, it is not clear how I should add this functionality.
I'm thinking that maybe this macro is over-complex, due to my inexperience in writing macros; and perhaps if I simplify it, modification will be easier. I don't really want to separate it out into several smaller macros without good reason; but maybe there's a terser way to write it?
Can anyone help me out here, please?
A complete code listing follows:
(defmacro with-gensyms ((&rest names) &body body)
`(let ,(loop for n in names collect `(,n (gensym)))
,#body))
(defmacro while (condition &body body)
`(loop while ,condition do (progn ,#body)))
(defun flatten (L)
"Converts a list to single level."
(if (null L)
nil
(if (atom (first L))
(cons (first L) (flatten (rest L)))
(append (flatten (first L)) (flatten (rest L))))))
(defun starts-with-p (str1 str2)
"Determine whether `str1` starts with `str2`"
(let ((p (search str2 str1)))
(and p (= 0 p))))
(defmacro pop-first-char (string)
`(with-gensyms (c)
(if (> (length ,string) 0)
(progn
(setf c (schar ,string 0))
(if (> (length ,string) 1)
(setf ,string (subseq ,string 1))
(setf ,string ""))))
c))
(defmacro pop-chars (string count)
`(with-gensyms (result)
(setf result ())
(dotimes (index ,count)
(push (pop-first-char ,string) result))
result))
(defun format-ansi-codes (text)
(let ((result ()))
(while (> (length text) 0)
(cond
((starts-with-p text "\\e")
(push (code-char #o33) result)
(pop-chars text 2)
)
((starts-with-p text "\\r")
(push (code-char 13) result)
(pop-chars text 2)
)
(t (push (pop-first-char text) result))
))
(setf result (nreverse result))
(coerce result 'string)))
(defun kv-lookup (values key)
"Like getf, but works with 'keys as well as :keys, in both the list and the supplied key"
(setf key (if (typep key 'cons) (nth 1 key) key))
(while values
(let ((k (pop values)) (v (pop values)))
(setf k (if (typep k 'cons) (nth 1 k) k))
(if (eql (symbol-name key) (symbol-name k))
(return v)))))
(defun make-ansi-escape (ansi-name)
(let ((ansi-codes '( :normal "\\e[00m" :white "\\e[1;37m" :light-grey "\\e[0;37m" :dark-grey "\\e[1;30m"
:red "\\e[0;31m" :light-red "\\e[1;31m" :green "\\e[0;32m" :blue "\\e[1;34m" :dark-blue "\\e[1;34m"
:cyan "\\e[1;36m" :magenta "\\e[1;35m" :yellow "\\e[0;33m"
:bg-dark-grey "\\e[100m"
:bold "\\e[1m" :underline "\\e[4m"
:start-of-line "\\r" :clear-line "\\e[2K" :move-up "\\e[1A")))
(format-ansi-codes (kv-lookup ansi-codes ansi-name))
))
(defun format-ansi-escaped-arg (out-stream arg)
(cond
((typep arg 'symbol) (format out-stream "~a" (make-ansi-escape arg)))
((typep arg 'string) (format out-stream arg))
(t (format out-stream "~a" arg))
))
(defun format-ansi-escaped (out-stream &rest args)
(while args
(let ((arg (pop args)))
(if (typep arg 'list)
(let ((first-arg (eval (first arg))))
(format out-stream first-arg (second arg))
)
(format-ansi-escaped-arg out-stream arg)
))
))
(defmacro while-pop ((var sequence &optional result-form) &rest forms)
(with-gensyms (seq)
`(let (,var)
(progn
(do () ((not ,sequence))
(setf ,var (pop ,sequence))
(progn ,#forms))
,result-form))))
(defun report-start (form)
(format t "( ) '~a'~%" form))
(defun report-result (result form)
(format-ansi-escaped t "(" (if result :green :red) `("~:[FAIL~;PASS~]" ,result) :normal `(") '~a'~%" ,form))
result)
(defmacro ? (name &body body-forms)
"Run any number of test forms, optionally nested within further (?) calls, and print the results of each test"
(with-gensyms (result indent indent-string)
(if (not body-forms)
:empty
(progn
(setf result () indent 0 indent-string " ")
(cond
((typep (first body-forms) 'integer)
(setf indent (pop body-forms))))
`(progn
(format t "~v#{~A~:*~}" ,indent ,indent-string)
(format-ansi-escaped t "[" :white ,name :normal "]~%")
(with-gensyms (test-results)
(setf test-results ())
,(while-pop (body-form body-forms `(progn ,#(nreverse result)))
(cond
( (EQL (first body-form) '?)
(push `(progn
(setf test-results (append test-results (? ',(nth 1 body-form) ,(1+ indent) ,#(nthcdr 2 body-form))))
(format t "~%")
test-results
) result)
)
(t
(push `(progn
(format t "~v#{~A~:*~}" ,(1+ indent) ,indent-string)
(report-start ',body-form)
(with-gensyms (result label)
(setf result ,body-form)
(format-ansi-escaped t :move-up :start-of-line :clear-line)
(format t "~v#{~A~:*~}" ,(1+ indent) ,indent-string)
(push (report-result result ',body-form) test-results)
test-results
)) result))))))))))
(defun ?? (&rest results)
"Run any number of tests, and print a summary afterward"
(setf results (flatten results))
(format-ansi-escaped t "~&" :white "Results: " :green `("~a test~:p passed" ,(count t results)) :normal ", "
(if (find NIL results) :red :normal) `("~a test~:p failed" ,(count NIL results))
:yellow `("~[~:;, ~:*~a test~:p not run~]" ,(count :skip results))
:brown `("~[~:;, ~:*~a empty test group~:p skipped~]" ,(count :empty results))
:normal "~%"))
For my part, the ? macro is rather technical and it's hard to follow the logic behind the formatting functions. So instead of tracking errors I'd like to suggest my own attempt, perhaps it'll be of use.
I think that actually your ?? doesn't want to evaluate anything, but rather to treat its body as individual tests or sections. If the body includes a list starting with ?, this list represents a section; other elements are test forms optionally followed by descriptions. So in my implementation ?? will be a macro, and ? will be just a symbol.
I start with wishful thinking. I suppose I can create individual tests using a function make-test-item and test sections using a function make-test-section (their implementation is unimportant for now), that I can display them using an auxiliary function display-test and compute results using the function results, which returns two values: the total number of tests and the number of passed ones. Then I'd like the code
(??
(? "Arithmetic tests"
(? "Addition"
(= (+ 1 2) 3) "Adding 1 and 2 results in 3"
(= (+ 1 2 3) 6)
(= (+ -1 -3) 4))
(? "Subtraction"
(= (- 1 2) 1)))
(= (sin 0) 0) "Sine of 0 equals 0")
to expand into something like
(let ((tests (list (make-test-section :header "Arithmetic tests"
:items (list (make-test-section :header "Addition"
:items (list (make-test-item :form '(= (+ 1 2) 3)
:description "Adding 1 and 2 results in 3"
:passp (= (+ 1 2) 3))
(make-test-item :form '(= (+ 1 2 3) 6)
:passp (= (+ 1 2 3) 6))
(make-test-item :form '(= (+ -1 -3) 4)
:passp (= (+ -1 -3) 4))))
(make-test-section :header "Subtraction"
:items (list (make-test-item :form '(= (- 1 2) 1)
:passp (= (- 1 2) 1))))))
(make-test-item :form '(= (sin 0) 0)
:passp (= (sin 0) 0)
:description "Sine of 0 equals 0"))))
(loop for test in tests
with total = 0
with passed = 0
do (display-test test 0 t)
do (multiple-value-bind (ttl p) (results test)
(incf total ttl)
(incf passed p))
finally (display-result total passed t)))
Here a list of tests is created; then we traverse it printing each test (0 denotes the zero level of indentation and t is as in format) and keeping track of the results, finally displaying the total results. I don't think explicit eval is needed here.
It may not be the most exquisite piece of code ever, but it seems manageable. I supply missing definitions below, they are rather trivial (and can be improved) and have nothing to do with macros.
Now we pass on to the macros. Consider both pieces of code as data, then we want a list processing function which would turn the first one into the second. A few auxiliary functions would come in handy.
The major task is to parse the body of ?? and generate the list of test to go inside the let.
(defun test-item-form (form description)
`(make-test-item :form ',form :description ,description :passp ,form))
(defun test-section-form (header items)
`(make-test-section :header ,header :items (list ,#items)))
(defun parse-test (forms)
(let (new-forms)
(loop
(when (null forms)
(return (nreverse new-forms)))
(let ((f (pop forms)))
(cond ((and (listp f) (eq (first f) '?))
(push (test-section-form (second f) (parse-test (nthcdr 2 f))) new-forms))
((stringp (first forms))
(push (test-item-form f (pop forms)) new-forms))
(t (push (test-item-form f nil) new-forms)))))))
Here parse-test essentially absorbs the syntax of ??. Each iteration consumes one or two forms and collects corresponding make-... forms. The functions can be easily tested in REPL (and, of course, I did test them while writing).
Now the macro becomes quite simple:
(defmacro ?? (&body body)
`(let ((tests (list ,#(parse-test body))))
(loop for test in tests
with total = 0
with passed = 0
do (display-test test 0 t)
do (multiple-value-bind (ttl p) (results test)
(incf total ttl)
(incf passed p))
finally (display-result total passed t))))
It captures a few symbols, both in the variable name space and in the function one (the expansion may contain make-test-item and make-test-section). A clean solution with gensyms would be cumbersome, so I'd suggest just moving all the definitions in a separate package and exporting only ?? and ?.
For completeness, here is an implementation of the test API. Actually, it's what I started coding with and proceeded until I made sure the big let-form works; then I passed on to the macro part. This implementation is fairly sloppy; in particular, it doesn't support terminal colours and display-test can't even output a section into a string.
(defstruct test-item form description passp)
(defstruct test-section header items)
(defun results (test)
(etypecase test
(test-item (if (test-item-passp test)
(values 1 1)
(values 1 0)))
(test-section (let ((items-count 0)
(passed-count 0))
(dolist (i (test-section-items test) (values items-count passed-count))
(multiple-value-bind (i p) (results i)
(incf items-count i)
(incf passed-count p)))))))
(defparameter *test-indent* 2)
(defun display-test-item (i level stream)
(format stream "~V,0T~:[(FAIL)~;(PASS)~] ~:['~S'~;~:*~A~]~%"
(* level *test-indent*)
(test-item-passp i)
(test-item-description i)
(test-item-form i)))
(defun display-test-section-header (s level stream)
(format stream "~V,0T[~A]~%"
(* level *test-indent*)
(test-section-header s)))
(defun display-test (test level stream)
(etypecase test
(test-item (display-test-item test level stream))
(test-section
(display-test-section-header test level stream)
(dolist (i (test-section-items test))
(display-test i (1+ level) stream)))))
(defun display-result (total passed stream)
(format stream "Results: ~D test~:P passed, ~D test~:P failed.~%" passed (- total passed)))
All the code is licenced under WTFPL.