% n  ident  [identity-matrix]
% create an identity matrix of dimension n*n.
% Uses a local dictionary for its one parameter, perhaps overkill.
% Constructs arrays of arrays of integers using [], for loops, and stack manipulation.
/ident { 1 dict begin /n exch def
    [
    1 1 n {                              % [ i
        [ exch                           % [ [ i
        1 1 n {                          % [ [ i j
            1 index eq { 1 }{ 0 } ifelse % [ [ i b
            exch                         % [ [ b i
        } for                            % [ [ b+ i
        pop ]                            % [ [ b+ ]
    } for                                % [ [b+]+ ]
    ]
end } def