All being a "functional language" means is that it's easy to write with a particular paradigm in the language.
You certainly can write similar code in ML, Java, or C - or whatever language strikes your fancy. It just helps when the type system is lined up with that goal, such as forcing you to denote where side-effects occur, and ensuring only functions that expect side-effect based code can operate on them. (For what it's worth, I've used both ML and Scheme to write similar style code as part of a programming languages class; and similarly, the C code I write relies on the functional ideas as much as possible.)
I just like the combination of Haskell's syntax and type system, so I prefer it to something like C (where functions aren't exactly a first class datatype, and the type system is somewhat weaker).
You certainly can write similar code in ML, Java, or C - or whatever language strikes your fancy. It just helps when the type system is lined up with that goal, such as forcing you to denote where side-effects occur, and ensuring only functions that expect side-effect based code can operate on them. (For what it's worth, I've used both ML and Scheme to write similar style code as part of a programming languages class; and similarly, the C code I write relies on the functional ideas as much as possible.)
I just like the combination of Haskell's syntax and type system, so I prefer it to something like C (where functions aren't exactly a first class datatype, and the type system is somewhat weaker).