Of course Haskell is also a functional programming language.
But since nowadays most major programming languages support programming in functional style, calling a programming language “functional” sounds like a restriction rather than an enabling of many great features.
Instead I propose calling it an effect-control programming language, as the type-system not only captures the returned value of a function, but also the effects/the context from which it is returned. This means in particular, that effects are first-class and can be manipulated
In my opinion this is the most important difference between other programming languages like Scheme or Python and Haskell.