[Haskell-cafe] tree insert and laziness

[Semen Trygubenko / Семен Тригубенко]

Dear Haskell-Cafe,

I'm presently reviewing a translation of the following paragraph
(taken from LUaH, chapter 8):

http://learnyouahaskell.com/making-our-own-types-and-typeclasses

"In languages like C, we'd do this by modifying the pointers
and values inside the tree. In Haskell, we can't really modify our tree,
so we have to make a new sub-tree each time we decide to go left
or right and in the end the insertion function returns a completely new tree,
because Haskell doesn't really have a concept of pointer, just values.
Hence, the type for our insertion function is going
to be something like a -> Tree a - > Tree a. It takes an element and a tree
and returns a new tree that has that element inside.
This might seem like it's inefficient but laziness takes care of that
problem."

If it is really the laziness that makes this approach efficient?
If it isn't, what did the author want to say in the last sentence?

Thank you,
Semen


-- 
Семен Тригубенко http://trygub.com
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