How do I convert an argument list to a sequence of arguments?

It seems I have found the answer: Apply.

Apply[f, {a, b, c, d}]

gives the output:

f[a, b, c, d]

The short infix syntax for Apply (at levelspec 0) is @@:

f @@ {a, b, c, d}

f[a, b, c, d]

Of course Apply, but also:

 f[{a, b, c, d} /. List -> Sequence]

f[a, b, c, d]

(my finger is hovering above the 'close' link, though)

A case not covered yet is if the argument list is held.

Starting with a dummy argument list, held:

args = Hold[{2+2, 8/4}];

and a dummy head (function) that also that holds its arguments, for illustration:

SetAttributes[foo, HoldAll]

Here are some options:

foo @@@ args // First

foo @@@ args // ReleaseHold

args /. _[{x___}] :> foo[x]

All yield:

foo[2 + 2, 8/4]

---

As rcollyer reminds, and I was remiss not to include, Hold can of course have multiple arguments itself therefore a simple Apply can work here:

foo @@ Hold[2+2, 8/4]

foo[2 + 2, 8/4]

Nevertheless sometimes the other format is produced and I hope that my examples prove useful in other circumstances.