sudo , 3 months ago

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.

<span style="color:#323232;">x </span><span style="font-weight:bold;color:#a71d5d;">= </span><span style="color:#0086b3;">2 </span><span style="font-weight:bold;color:#a71d5d;">:: </span><span style="color:#0086b3;">1 </span><span style="font-weight:bold;color:#a71d5d;">:: </span><span style="color:#0086b3;">Nil </span><span style="font-style:italic;color:#969896;">-- [2, 1]
</span><span style="color:#323232;">y </span><span style="font-weight:bold;color:#a71d5d;">= </span><span style="color:#0086b3;">3 </span><span style="font-weight:bold;color:#a71d5d;">::</span><span style="color:#323232;"> x </span><span style="font-style:italic;color:#969896;">-- [3, 2, 1]
</span>

In this example both x and y are single linked lists. y is a node with value 3 and a pointer to x. If x was mutable then changing x would change y. 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