Octave: Help with implementing midpoint rule

[MaxManus]

I got the code from my textbook and it is supposed to work in matlab

function r = midpoint(a,b,f,n)
f = fcnchk(f);
h = (b-a)/n;
x = (a+h*0.5):h:(b-h*0.5);
y = feval(f,x);
r = h*sum(y(1:n));

The code fails on feval

I go tcnchk from wikipedia

function f=fcnchk(x, n)
  f = x;
end

and I use f = 'x.^2' as f

Can someone help me?
I don't know how to copy the error from Octave

 

[Mark44]

How about you look at the error and write it down, then post it here?