Octave call a function as a variable of another function

I wrote a bisection method in Octave but it can't consume another function..

My bisection method code is like:

function[x,b] = bisection(f,a,b)

  t = 10e-8

  while abs(b-a) > t;
    c = (a+b)/2;

    if f(a) * f(b) <= 0
       a = a;
       b = c;
    else 
       b = b;
       a = c
    endif
  endwhile

  x = (a+b)/2
endfunction

And I already have a file f1.m:

function y = f1(x)
  y = x^2 - 4;
endfunction

But when I call [x,v] = bisection[f1,0,5], I get:

>> [t,v] = bisection(f1,0,5)
   error: 'x' undefined near line 2 column 5
   error: called from
          f1 at line 2 column 3
   error: evaluating argument list element number 1