[throwaway17_17]

Your assumption is somewhat correct, for both Erlang and Elixir, however the phrase under discussion doesn’t mean the same thing for immutable languages. Both are ‘pass-by-value’ but that term is being overloaded in a particular way. As I said in another comment, ‘value’ in the language from TFA means any object that IS NOT a reference. The qualifier that every semantic object is a ‘value’ and that therefore, all arguments to a function call, threads spawn, etc are independent values which are (logically, at least) copied to new values that are then passed to the new context.

However, for Erlang and Elixir ‘pass-by-value’ is otherwise called ‘call-by-value’. In this case, it is a statement that arguments to functions are evaluated before they are passed into the function (often at the call site). This is in opposition to ‘call-by-name/need’ (yes, I know they aren’t the same) which is, for instance, how Haskell does it for sure, and I think Python is actually ‘by-name’ as well.

So, Herd’s usage here is a statement of semantic defaults (and the benefits/drawbacks that follow from those defaults) for arguments to functions, and Elixir’s usage is about the evaluation order of arguments to functions, they really aren’t talking about the same thing.

Interestingly, this is also a pair of separate things, which are both separate from what another commenter was pedantically pointing out elsewhere in the thread. Programming language discussion really does seem to have a mess of terminology to deal with.