%!PS

% begin included library code
% see https://codeberg.org/Firedrake/postscript-libraries/
/test {
    /test.count test.count 1 add def
    {
        /test.pass test.pass 1 add def
    } {
        ( ) print
        test.count (....) cvs print
        (-fail) print
    } ifelse
} bind def

/test.start {
    print (:) print
    /test.pass 0 def
    /test.count 0 def
} bind def

/test.end {
    ( ) print
    test.count 0 gt {
        (Passed ) print
        test.pass (...) cvs print
        (/) print
        test.count (...) cvs print
        ( \() print
        test.pass 100 mul test.count idiv (...) cvs print
        (%\)) print
        (\r\n) print
    } if
} bind def

/all { % [a b] proc -> bool
    1 dict begin
    /p exch def
    true exch
    {
        p not {
            pop false
            exit
        } if
    } forall
    end
} bind def


% end included library code

/boomerang {
    0 dict begin
    /a exch def
    /done false def
    false
    % coincident points
    /delta [
        0 1 1 {
            /ij exch def
            ij 1 add 1 2 {
                /ik exch def
                a ij get 0 get a ik get 0 get eq
                a ij get 1 get a ik get 1 get eq and {
                    pop false
                    /done true def
                } if
            } for
            [
                a ij 1 add get 0 get a 0 get 0 get sub
                a ij 1 add get 1 get a 0 get 1 get sub
            ]
        } for
    ] def
    % all on the same vertical line
    done not {
        delta 0 get 0 get 0 eq
        delta 1 get 0 get 0 eq and {
            pop false
            /done true def
        } if
    } if
    % just one vertical line
    done not {
        delta 0 get 0 get 0 eq
        delta 1 get 0 get 0 eq or {
            pop true
            /done true def
        } if
    } if
    done not {
        /m delta 0 get 1 get cvr delta 0 get 0 get cvr div def
        /c a 0 get 1 get cvr a 0 get 0 get cvr m mul sub def
        pop a 2 get 1 get cvr a 2 get 0 get cvr m mul c add ne
    } if
    end
} bind def

(boomerang) test.start
[[1 1] [2 3] [3 2]] boomerang test
[[1 1] [2 2] [3 3]] boomerang not test
[[1 1] [1 2] [2 3]] boomerang test
[[1 1] [1 2] [1 3]] boomerang not test
[[1 1] [2 1] [3 1]] boomerang not test
[[0 0] [2 3] [4 5]] boomerang test
test.end