postscript Error Handling Re-throwing errors

Example

This snippet implements a procedure which behaves like a postscript looping operator. If the user proc calls exit, it catches the invalidexit error to fix the dictstack for the end at the end. Any other error except invalidexit is re-thrown by calling stop.

% array n proc  .  -
% Like `forall` but delivers length=n subsequences produced by getinterval
/fortuple { 4 dict begin
    0 {offset proc n arr} {exch def} forall
    /arr load length n idiv
    {
        {
            /arr load offset n getinterval
            [ /proc load currentdict end /begin cvx ] cvx exec
            /offset offset n add def
        } stopped {
            $error /errorname get /invalidexit eq
            { 1 dict begin exit }{ stop } ifelse
        } if
    } repeat
end
} def

%[ 0 1 10 {} for ] 3 {} fortuple pstack clear ()=