Author: [William C Wickes]
  Date: Thu Apr 11 1991

Given x and F on the stack, where x is any argument, and F is a
function of one argument (user-defined or built-in), the following
program returns 'F(x)':

%%HP: T(3)A(R)F(.);
@ x F -> 'F(x)'
\<< SWAP -> a
   \<< 'a' SWAP EVAL                   @ 'F(a)'
       'a' a 2 \->LIST \|^MATCH DROP   @ 'F(x)'
   \>>
\>>

To put a built-in function F on the stack, execute { F } 1 GET.  You
can also build this logic into the program above, and use { F } as the
argument.

For user-defined functions, you also can use SWAP 1 \->LIST SWAP APPLY.

Bill Wickes
HP Corvallis