[kristopolous]

I didn't say Haskell. There are numerous programmings languages which only permit pass by value (and no referencing) for "I'm-such-a-smartypants" reasons.

I was really bashing the single-paradigm purist approach in general. It's much too rigid and difficult for anyone who isn't a card carrying mensa member.

[lvh]

Do you mean pass-by-value semantics, or copy-values-for-the-caller implementation? If you mean semantics, then yes: FP languages tend to like value semantics. However, I don't see what that has to do with referencing; you can certainly allow only passing things by value, but only pass references: that's what Python and C (and many others!) do, for example.

It sounds like you may be conflating pass-by-reference with passing references.

If you mean implementation: which ones? In the context of immutable and often even persistent data structures, copying them doesn't make a whole lot of sense.