splicing list of optional arguments in function call

I don't know what exactly you are trying to do, but
maybe you can make your life simpler by not trying to
call foo again or using buildq.  Use a different function, and one with a
fixed number of arguments.  Like

foo(a,b,c,[z]):=
    if atom(a) then ....
        else if inpart(a,0)="=" then
            foo2 (lhs(a)-rhs(a), cons(b,cons(c,z)))

... foo2 always takes 2 arguments, an expression and a list.
...  good lick.

You should think twice before using buildq.  And then
think twice again.  Unless you require unconventional
evaluation of arguments, it is probably a mistake to
use it.

RJF

Albert Reiner wrote:
> Hi,
> 
> I have learnt here in the past (thanks!) that one can use an arbitrary
> number of arguments by using [symbol], rather than a symbol itself, as
> the last formal argument.  Now I have some function foo with optional
> arguments, and if the non-optional first argument is an equation I
> want to call foo again with the same arguments, but substituting the
> difference of left and right hand sides of the equation as the first
> argument.  Currently I have something like
> 
> foo(a,b,c,[z]) :=
>   if inpart(a,0) = "="
>   then
>     buildq([a: inpart(a,1)-inpart(a,2), b, c, z],
>            lambda([], foo(a,b,c,splice(z)))) ()
>   else
>     [ a, b, c, z ] $
> 
> Where I need the splice(z) to avoid getting an extra list around the
> optional arguments, and I need the buildq to be able to use splice,
> and I need the lambda([],...)() to evaluate the call, rather than
> getting an unevaluated foo(...) expression.  This seems to work, but
> is there a simpler way?
> 
> Thanks in advance,
> 
> Albert.
> 
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