There are already tools for performing these tasks. Check out the InputParser class [ ref, ref ]. It will allow you to declare three sets of arguments: required, optional, and param/value pairs. For each parameter, you will be able to define a check function, as well as a default value for all but required parameters.
EDIT: just as an example, here is the beginning of a function using an input parser
function [hFig, hAxis, hLegend, hPatches] = bar_varWidth( colWidth, ...
data, varargin )
% --- 1. Parse input parameters.
parser = inputParser ;
parser.StructExpand = true ;
parser.CaseSensitive = false ;
parser.addRequired( 'colWidth', @isnumeric ) ;
parser.addRequired( 'data', @isnumeric ) ;
parser.addParamValue( 'legend', [], @(x) ischar(x) || iscell(x) ) ;
parser.addParamValue( 'xTickLabel', [], @(x) isnumeric(x) || iscell(x) ) ;
parser.addParamValue( 'xTickLabelFormat', '%.2f', @ischar ) ;
parser.addParamValue( 'xTickLabelShiftThreshold', 10, @isnumeric ) ;
parser.addParamValue( 'xTickLabelAngle', 90, @isnumeric ) ;
parser.addParamValue( 'xTickLabelLineLength', [], @isnumeric ) ;
parser.parse( colWidth, data, varargin{:} ) ;
args = parser.Results ;
% --- 2. ...
and here all parameters are accessible as fields of args, e.g.
args.colWidth
args.legend
