What I am saying is mutability is not something that tends to stay local. Either you isolate it at the top, ala Haskell or it tends to find it's way into everything.
SSA is great, except that as you say it is functionally equivalent to immutability. There is no advantage to it over using immutable data structures. In fact, it is inferior as it only covers a subset of problems that immutability does.
The examples in the blog post illustrate this. He wants to make local variables mutable because otherwise he can't pass a reference to a function which mutates a value. That mutation is completely unnecessarily and could of been performed with a pure function instead.
Note the blog author says: "Think: when was the last time you responded to a compiler error about illegal mutation by doing anything other than restructuring the code to make the mutation legal?"
I actually do this all the time. That is probably the largest challenge coming to a language like Haskell from an imperative background. Sometimes you can't just fix the little mutability problem locally, it has to be redesigned with immutability in mind.
SSA is great, except that as you say it is functionally equivalent to immutability. There is no advantage to it over using immutable data structures. In fact, it is inferior as it only covers a subset of problems that immutability does.
The examples in the blog post illustrate this. He wants to make local variables mutable because otherwise he can't pass a reference to a function which mutates a value. That mutation is completely unnecessarily and could of been performed with a pure function instead.
Note the blog author says: "Think: when was the last time you responded to a compiler error about illegal mutation by doing anything other than restructuring the code to make the mutation legal?"
I actually do this all the time. That is probably the largest challenge coming to a language like Haskell from an imperative background. Sometimes you can't just fix the little mutability problem locally, it has to be redesigned with immutability in mind.