/print {dup ==} def

% /f /df x0 N

/newton {
4 dict begin
/N exch def
/x0 exch def
/df exch cvx def
/f exch cvx def

(a) ==

x0

N {

(b) ==

% x on stack
dup dup			% x x x

print

f				% x x fx

print
( x, fx --------------------) ==
 
exch df			% x fx dfx
div sub			% x - fx/dfx

} repeat

dup f exch		% fx x on stack

end
} def

% testing -------------------------------------

% x*x - 2

/square {dup mul 2 sub} def
/dsquare {2 mul} def

/E 2.718281828 def

% x - exp(-x), 1 + exp(-x)

/F {
dup neg			% x -x
E exch exp 		% x e^-x
sub 
} def

/dF { 
neg E exch exp		% e^-x
1 exch				% 1 e^-x
add
} def

/F /dF 1 10 newton