this post was submitted on 15 Apr 2024
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No. Persistent Data Structures are not mutable. The memory space of an older version is not rewritten, it is referenced by the newer version as a part of its definition. ie via composition. It can only safely do this if the data it references is guaranteed to not change.
In this example both
x
andy
are single linked lists.y
is a node with value3
and a pointer tox
. Ifx
was mutable then changingx
would changey
. That's bad™ so its not allowed.If you want to learn more about functional programming I suggest reading Structures and Interpretation of Computer Programs or Learn You a Haskell for Great Good