What is a functional language - something that encourages programming in a functional style, or actively outlaws imperative programming? IMO it's pleasant to u

What is a functional language - something that encourages programming in a functional style, or actively outlaws imperative programming? IMO it's pleasant to use Ruby in a functional style, much more pleasant than Python owing to the ease of chaining calls that take lambda arguments (blocks). Every time I try to do something similar to a big chained Enumerator stream in Ruby in Python using a list comprehension, I have to invert my thinking - as far as I'm concerned, those things are written backwards and inside out.