indentation doesn't work for complex situations

[caox]

case expression of
    pattern when guard ->
        body
    end

    try expression of
        pattern when guard ->
            wath
            catch
                pattern when guard ->
                    body
                    after
                        body
                    end  

The indentation doesn't work properly when use command tab to indent the source code. It seems the increaseIndentPattern and decreaseIndentPattern are too simple to match all the cases.