You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: feval.m
    path of file: ./repos/chebfun/@diskfun
    
    the code of the file until where you have to start completion: function y = feval(varargin)
%FEVAL   Evaluate a DISKFUN at one or more points.

    
function y = feval(varargin)
%FEVAL   Evaluate a DISKFUN at one or more points.
%   Y = FEVAL( F, X, Y) evaluates a diskfun F at a point (X,Y) in Cartesian
%   cooridnates, where X and Y are doubles.
%
%   Y = FEVAL( F, THETA, R, 'polar') evaluates a diskfun F in polar
%   coordinates (THETA,R).  Here THETA and R are doubles representing the
%   central angle (in radians) and radius in polar coordinates and must be
%   points in the unit disk.
%
%   Y = FEVAL(F, c), where c is a complex-valued chebfun representing a
%   contour, evaluates F along the contour.
%
% See also SUBSREF.

% Copyright 2017 by The University of Oxford and The Chebfun Developers.
% See http://www.chebfun.org/ for Chebfun information.

% Figure out if Cartesian or polar coordinates should be used.
iscart = 1;
% Search for user-supplied 'polar' flag in arguments:
isPolar = find(strcmp(varargin, 'polar'));
if ( any( isPolar ) )
    iscart = 0;
end