Intergration of expotential function using simpsons rule

I try to do intergration using simpsons rule. Each and every time l use the function simprule it gives me error, "undefined function or variable". How could l define the function more than what l did. Below is my code

%SIMPRULE Simpsons rule integration.

% I = SIMPRULE(F, A, B, N) returns Simpsons rule approximation

% for the integral of f(x) from x=A to x=B, using N subintervals,

% where F is a function handle.

f=@exp(x)

a=0

b=1

n=2

I = simprule(f, a, b, n)

h = (b-a) / n;

x = a:h:b; % an array of length n+1

S = 0;

L = 0;

for l = 1:2:n %generates the odd number array

S = S + 4*f(x(l));

end

for j = 2:2:n % generates the even number array

L = L + 2*f(x(j));

end

I = (h/3)*(f(a)+ S + L + f(x(n)));