Using builtin PARI operators in gp

Up to some extent, one can “reach” the builtin PARI operators in gp:

  (20:25) gp > ?_+_
  x+y: sum of x and y.

  (20:00) gp > ?+_
  +_: copy and return its argument

Should not there be a way to specify these functions as arguments to
other gp functions?  Something like

  SUM = fold(array, `"_+_");

?

Hope this helps,
Ilya