DeclareDocumentCommand{myMacro} {o o}
{
   DeclareDocumentCommand{foo} {} {#1}
   DeclareDocumentCommand{bar} {} {#2}
   The foo argument was foo and the bar argument was bar

}

documentclass{article}
usepackage{keyval,xparse}% http://ctan.org/pkg/{keyval,xparse}

makeatletter
% ========= KEY DEFINITIONS =========
define@key{mymacro}{first}{defmm@first{#1}}
define@key{mymacro}{second}{defmm@second{#1}}
define@key{mymacro}{third}{defmm@third{#1}}
define@key{mymacro}{last}{defmm@last{#1}}
DeclareDocumentCommand{myMacro}{m}{%
  begingroup%
  % ========= KEY DEFAULTS + new ones =========
  setkeys{mymacro}{first={FIRST arg},second={SECOND arg},third={THIRD arg},last={LAST arg},#1}%
  First arg: mm@first par
  Second arg: mm@second par
  Third arg: mm@third par
  Last arg: mm@last
  endgroup%
}
makeatother

begin{document}

myMacro{last=LaSt,first=FiRsT} par hrulefill

myMacro{} par hrulefill

myMacro{third={$x^2$ textbf{stuff}},second={}}
end{document}

documentclass{article}
usepackage{keyval,xparse,url}% http://ctan.org/pkg/{keyval,xparse,url}

makeatletter
% ========= KEY DEFINITIONS =========
define@key{movie}{title}{expandafterdefcsname movietag @titleendcsname{#1}}
define@key{movie}{releaseyear}{expandafterdefcsname movietag @releaseyearendcsname{#1}}
define@key{movie}{genre}{expandafterdefcsname movietag @genreendcsname{#1}}
define@key{movie}{url}{expandafterdefcsname movietag @urlendcsname{#1}}
DeclareDocumentCommand{newMovie}{m m}{%
  % ========= KEY DEFAULTS + new ones =========
  defmovietag{#1}% Store movie tag (used when setting/storing keys)
  setkeys{movie}{title={},releaseyear={},genre={},url={},#2}% Create keys
}
DeclareDocumentCommand{showMovie}{m}{%
  textbf{csname #1@titleendcsname} (csname #1@releaseyearendcsname),
  textit{csname #1@genreendcsname},
  expandafterexpandafterexpandafterurlexpandafterexpandafterexpandafter{csname #1@urlendcsname}.
}
makeatother

begin{document}

% Movie declarations
newMovie{anchorman2}{
  url={http://www.imdb.com/title/tt1229340/},
  releaseyear=2013,
  title={Anchorman: The Legend Continues},
  genre=Comedy}
newMovie{lego}{
  title={The Lego Movie},
  releaseyear=2014,
  url={http://www.imdb.com/title/tt1490017/},
  genre={Animation, Action, Comedy}}
newMovie{magic}{
  title={Now You See Me},
  url={http://www.imdb.com/title/tt1670345/},
  releaseyear=2013,
  genre={Crime, Thriller}}

% Show movie details
showMovie{magic}

showMovie{anchorman2}

showMovie{lego}

end{document}

documentclass{article}
usepackage{xparse,url}

ExplSyntaxOn
% keys
keys_define:nn { oxinabox/movies }
 {
  title .tl_set:N = l_oxinabox_title_tl,
  releaseyear .tl_set:N = l_oxinabox_releaseyear_tl,
  genre .tl_set:N = l_oxinabox_genre_tl,
  url .tl_set:N = l_oxinabox_url_tl,
 }

% user level commands
NewDocumentCommand{newMovie}{m m}
 {
  oxinabox_newmovie:nn { #1 } { #2 }
 }

NewDocumentCommand{showMovie}{m}
 {
  oxinabox_showmovie:n { #1 }
 }

% internal functions
cs_new_protected:Npn oxinabox_newmovie:nn #1 #2
 {
  group_begin: % keep the assignment to the keys local
  prop_new:c { g_oxinabox_movie_#1_prop }
  keys_set:nn { oxinabox/movies } { #2 }
  prop_gput:cnV { g_oxinabox_movie_#1_prop } { title } l_oxinabox_title_tl
  prop_gput:cnV { g_oxinabox_movie_#1_prop } { releaseyear } l_oxinabox_releaseyear_tl
  prop_gput:cnV { g_oxinabox_movie_#1_prop } { genre } l_oxinabox_genre_tl
  prop_gput:cnV { g_oxinabox_movie_#1_prop } { url } l_oxinabox_url_tl
  group_end:
 }

cs_new:Npn oxinabox_getvalue:nn #1 #2
 {
  prop_item:cn { g_oxinabox_movie_#1_prop } { #2 }
 }
cs_new_protected:Npn oxinabox_showmovie:n #1
 {
  parnoindent
  textbf{ oxinabox_getvalue:nn { #1 } { title } }, ~ %
  textbf{ oxinabox_getvalue:nn { #1 } { releaseyear } }, ~ %
  textbf{ oxinabox_getvalue:nn { #1 } { genre } },
  \
  use:x { exp_not:N url { oxinabox_getvalue:nn { #1 } { url } } }
}
ExplSyntaxOff
begin{document}

% Movie declarations
newMovie{anchorman2}{
  url={http://www.imdb.com/title/tt1229340/},
  releaseyear=2013,
  title={Anchorman: The Legend Continues},
  genre=Comedy}
newMovie{lego}{
  title={The Lego Movie},
  releaseyear=2014,
  url={http://www.imdb.com/title/tt1490017/},
  genre={Animation, Action, Comedy}}
newMovie{magic}{
  title={Now You See Me},
  url={http://www.imdb.com/title/tt1670345/},
  releaseyear=2013,
  genre={Crime, Thriller}}

% Show movie details
showMovie{magic}

showMovie{anchorman2}

showMovie{lego}

end{document}