args-macro question

[Jeremy Dunn]

I am writing a macro in which the argument list ends with one or more lists. In my macro I am trying to get the index at which the lists start so I can slice them out. So I write something like this



(define-macro (func)

  (setq cnt (first (index list? (args))))

)



but when I do this NewLISP squawks. What am I doing wrong?

[cormullion]

Looks like it works a bit...

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newLISP v.8.8.9 on OSX UTF-8, execute 'newlisp -h' for more info.
> (define-macro (func) (set 'cnt (first (index list? (args)))))
(lambda-macro () (set 'cnt (first (index list? (args)))))
> (func "1" (list (sequence 1 2 3)))
1
>


[Lutz]

this works for me:

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> (define-macro (func) (nth (first (index list? (args))) (args)))
(lambda-macro () (nth (first (index list? (args))) (args)))
> (func 1 2 (a b c))
(a b c)
> (func 1 2 (a b c) 4 5)
(a b c)
>


always returns the first list argument found. But you can make it shorter using 'filter':

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> (define-macro (func) (first (filter list? (args))))
(lambda-macro () (first (filter list? (args))))
> (func 1 2 (a b c) 4 5)
(a b c)
>


or even shorter using implicit indexing:

Code Select Expand


> (define-macro (func) ((filter list? (args)) 0))
(lambda-macro () ((filter list? (args)) 0))
> (func 1 2 (a b c) 4 5)
(a b c)
>




Lutz

[Jeremy Dunn]

Deleted message - Lutz posted before I did - Thanks!

[Jeremy Dunn]

Still have a question about the lambda-macro statement and what that is doing. When I look in my function listings I see fn, lambda and lambda? but I don't find any reference to lambda-macro. Sorry to be so dense but what is lambda-macro and what is it doing to the previous statement?

[Lutz]

'lambda-macro' has the same relation to 'define-macro' as 'lambda' has to 'define', but 'lambda-macro' is not present in the index/manual. It will be added. 'fn' is just a shorter form for writing 'lambda'.





Lutz