Hi. Need help with creating the 'for' macro. It must take a parameter, an initial value, an end value, and a loop step. Macro must return amount of iteration. Various operations should take place inside it. It should be designed without leaks.The preliminary version looks like this:
(defmacro for ((param-name start-value end-value &optional (step1 1)) &body body)
(let* ((func-name (gensym))
(start (gensym))
(param-name (gensym))
(comparison (if (< step1 0) '< '>))
(end (gensym))
(step (gensym))
(k (gensym)))
'(labels ((,func-name (,param-name ,start ,end ,step ,k)
(let ((new-exprs (progn ,@body))
(newK (+ 1 ,k)))
(if (,comparison ,end ,param-name)
(,func-name (+ ,param-name ,step) ,start ,end ,step newK)
newK))))
(,func-name ,param-name ,start-value ,end-value ,step1 0))))
I understand that it looks terrible. I don't understand how you can access the parameter without violating the rule about leaks.
Make sure that the new form evaluates the macro arguments in the correct order. The LET enforces it.
Now you would need to think what to do about the step thing.
Can it only be a number? Can it be computed? What if the step value is negative?
How to check that the PARAM-NAME is actually a symbol?
Write some test cases.
Thanks man!
Do you know if it is possible to evaluate the value of body without entering a new variable?
sure, remove the LET
(defmacro for
((param-name start-value end-value &optional (step1 1)) &body body)
(let* ((func-name (gensym))
(comp (gensym))
(comparison (if (< step1 0) '<= '>=))
(start (gensym))
(end (gensym))
(step (gensym))
(k (gensym)))
`(let ((,start ,start-value)
(,comp ,comparison)
(,end ,end-value)
(,step ,step1))
(labels ((,func-name (,param-name ,k)
(if (,comparison ,end ,param-name)
(progn (progn ,@body)
(,func-name (+ ,param-name ,step)
(1+ ,k)) ,k))))
(,func-name ,start 1)))))
Do you know how can I close leak with comparison? When I am trying to bound comp to evaluated operator of comparison I receive error.
Your indentation is wrong. The last
,kis at a wrong place. Shouldn't it be returned by the otherifclause.If you have an error and you need help, then you need to provide the necessary information:
(defmacro for
((param-name start-value end-value &optional (step1 1)) &body body)
(let* ((func-name (gensym))
(comp (gensym))
(comparison (if (< step1 0) '<= '>=))
(start (gensym))
(end (gensym))
(step (gensym))
(k (gensym)))
`(let ((,start ,start-value)
(,comp ,comparison)
(,end ,end-value)
(,step ,step1))
(labels ((,func-name (,param-name ,k)
(if (,comp ,end ,param-name)
(progn (progn ,@body)
(,func-name (+ ,param-name ,step)
(1+ ,k)) ) ,k)))
(,func-name ,start 0)))))
Sorry man. I kinda fixed the issue. When I am trying to call macros, it return me error
; compilation unit finished
; Undefined functions:
; #:G1 #:G7
; Undefined variable:
; >=
I don't know how to deal with bounding <= or >= to generated variable.
why would evaluate the comparison? The comparison is a symbol, which a name for the function. Just use that symbol and insert it into the code.
If you actually want to make sure that function does not get redefined, you need to understand that functions and variables are in different namespaces. You would need to get a function object and funcall it.
But you don't need that.
If you want to debug macros, you need to see the expansion. Do it like this: