I think it might help to point out how the macro expands there:
(inl 1 '(1 2 3))
is transformed by the reader to
(inl 1 (quote (1 2 3)))
which is then macro expanded by
`(in ,elt ,@lst)
where elt is bound to '1, and lst is bound to '(quote (1 2 3)). This means that when lst is spliced in, you get:
'(in 1 quote (1 2 3))
As stated, the problem is largely the choice of macro instead of function. Macros are primarily useful to control evaluation; they do not evaluate their arguments by default. A macro will only let you work with the literal input, not their values. You can't (with arc) have your cake and eat it too; you can only work with either the syntax, or the values. You wouldn't be able to do something like:
(let x '(1 2 3)
(inl 1 x))
for instance, because it would attempt to treat the symbol 'x as if it were a list to be spliced, not the value of x. That's why you need a function, like pos.
