expr = 2
-------------
expr = 7
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((y_ >> x_ + 2*y_)) ---> lazy function : (_2) --> (_1 + (2 * _2))
(x_ >> (y_ >> x_ + 2*y_ )) ---> lazy function : (_1) --> lazy function : (_2) --> (_1 + (2 * _2))
 r >> = lazy function : (_2) --> (_1 + (2 * _2))
 r2 >> = lazy function : (_1) --> lazy function : (_2) --> (_1 + (2 * _2))
expr = (_1 + (2 * _2))
expr = 7
(tql::eval ( make_function(x_ + 2*y_ , x_) , y_ = 2) (3)) ---> 7
(make_function(x_ + 2 , x_) (3)) ---> 5
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expr = ((_1 + (2 * _2)) + _3)