(mac foo(a b) `(cons ,a ,b))
(apply foo '(1 (2 3)))
=> (cons 1 (2 3))
=> error: 2 is not a function
Basically you'd have to:
1. eval the list
2. cons the macro to the list, eval to yield the macroexpansion
3. implicitly eval the macroexpansion -- but not eval the elements of the spliced in list because they've already been eval'd once.
Step 3 throws a spanner in the works.
So you might say, fine, let's quote all the elements of the spliced in list. And that'll seem to work for the previous example, but you'll eventually run into an example like this:
(apply = '(x 3))
=> (= 'x '3)
=> error: can't assign to (quote x)
I've started implementing a Lisp interpreter in C# and I also was going along the path of making everything "first class" by using f-expressions where appropriate. So far my only actual f-expressions are "lambda" and "if" - everything else is bootstrapped as macros or functions.
My "apply" currently expects a function but I was toying with making it "eval" the cons macro... but then "apply" has to become an f-expression instead of just a plain normal function which seemed inelegant so I left it as a function that requires a function.
Reading your story... I think I'll leave it permanently side-stepped!! :-)
in takes any number of arguments, and returns whether the first argument is repeated in the rest of them:
Ok, let's say I have a list, and I want to find out whether something is in it: Oh dear. That's not right.The solution, at least in Arc, is to use mem:
It returns the first sub-list of its second argument such that the car of the returned list is the element searched for -- or 'nil if the element isn't in the list. So yes, you can make it work, in this case. But it's surely more confusing than having (apply in 2 (list 1 2 3)) work.