Define-macro & setf/$it

[newdep]

Hi Lutz,



Why is this behaviour?



'setf does evaluate the expression, so inside the macro

i would expect this to work. but i dont understand why not..

When I replace $it with (args 0) it also doesnt work..

..Probably a very logical explanation here..





-> (define-macro (z) (setf (args 0) (string $it)) )

(lambda-macro () (setf (args 0) (string $it)))

-> (z hello world)



ERR: no symbol reference found

->







Edit: Is it because (args) does not refer ? But i would expect this to be handled like a list..

[Lutz]

'setf' refers to a place not a symbol like the old 'set', so when you pass a symbol via a macro you have to use 'eval':

Code Select Expand

(define-macro (z) (setf (eval (args 0)) (string $it)) )
(setq hello 123)

(z hello) => "123"

hello => "123"


[newdep]

oke clear... now look here.. do you notice someting ? -->



-> (define-macro (z) (push (string (pop (args))) (args)) )

(lambda-macro () (push (string (pop (args))) (args)))

-> (z 'hello 'world)

("'hello" 'hello 'world)





The first 'hello became " 'hello " ... ?



while a (string 'hello) => "hello" and not " 'hello "



EDIT:

Im a little lost... also the fact that the (args) now has a double hello

as where i destructively popped it and pushed it..

So the 'pop returns the unchanged but the push is allowed)





EDIT2:

I just got a $.25c dropp ;-) thanks..got it..

[Lutz]

- you see quotes, because you are using 'define-macro' and you are passing quoted arguments



- (args) always returns a copy you cannot change args itself (which is a good thing ;-)). But you could do the following:

Code Select Expand

(define-macro (z)
(let (params (args))
(push (string (pop params)) params) ))

(z hello world) => ("hello" world)