problem with str2func

hello I am having a problem using str2func, when matlab says that the function i called to is 'undefined function 'X' for input or arguments of type 'double'.

There is a string which is stored in Shape. Shape gets its string from a function, which gives Shape different values randomly. I have a function for each shape, so for example if Shape gets the value square, there is also a function named square, and i want to call that function according to the string that is stored in Shape.

so i wrote this:

f=str2func(shape);
f(x0,y0);

function [] = vav(x0,y0)  
  x=[x0 x0+1 x0+1 x0+2 x0+2 x0];
  y=[y0 y0 y0+3 y0+3 y0+4 y0+4];

    patch(x,y,[0.3 0.2 0.45])
  end

so shape gets a string for example shape='vav'; but when i use f=str2func(shape) and i call f(x0,y0) it doesn't work.

how can i fix it? and what is wrong with this way? Thanks!!