[Haskell-cafe] efficient operations on immutable structures

[Christopher Howard]

Hi again all. From some online research, I understand that operations on
complex immutable structures (for example, a "setter" function a ->
(Int, Int) -> Matrix -> Matrix which alters one element in the Matrix)
is not necessarily inefficient in Haskell, because the (compiler?
runtime?) has some means of sharing unchanged values between the input
and output structure. What I am not clear on, however, is how this
works, and how you ensure that this happens. Could someone perhaps
elaborate, or point me to a really good read on the subject?

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