function REAL_FN(varargin)
%REAL_FN mark functions that should only output real numbers
%
% Example usage:
%     REAL_FN log log10
% or
%     REAL_FN('log', 'log10')
%
% Either of these lines of code will mean that calling log or log10 from the
% current workspace will result in an error if non-real numbers result. This is
% like doing: "log = @reallog", but can be applied to any function (there is no
% "reallog10" built into Matlab).
%
% Simply clear the variables that this function produces to remove its effect
% from builtins:
%
% clear log log10
%
% This command can be applied to function handles as well as builtins. If
% applied to function handles, keep a copy of the originals if you need to
% reinstate them.
%
% This adds overhead to all calls of the affected functions.
% It's intended for debugging only.

% Iain Murray, November 2009

for ff = varargin
    fn_name = ff{1};
    if ~ischar(fn_name)
        error(sprintf(['REAL_FN expects string arguments. Use one of:\n',...
                '    REAL_FN func1 func2 ...\n',...
                '    REAL_FN(''func1'', ''func2'', ...)']));
    end
    if evalin('caller', ['exist(''', fn_name, ''', ''var'')'])
        % function is a function handle in the caller.
        fn = evalin('caller', fn_name);
    else
        % function in the caller is an m-file, mex-file, pcode, ...
        fn = evalin('caller', ['@', fn_name]);
    end
    assignin('caller', fn_name, @(varargin) real_checker(fn, fn_name, varargin{:}));
end


function varargout = real_checker(fn, fn_name, varargin)

varargout = cell(1, max(1, nargout));
[varargout{:}] = fn(varargin{:});
for ii = 1:numel(varargout)
    if isnumeric(varargout{ii}) && ~isreal(varargout{ii})
        error(['Unwanted complex result from ''', fn_name, ''' detected.']);
    end
end