“Functional programming” has a clear meaning, but does “functional language”?

Question

I understand very clearly the difference between functional and imperative programming techniques. But there\'s a widespread tendency to talk of \"functional languages\

Answer 1

I like @Randolpho's answer. With regards to features, I might cite the list here:

Defining point of functional programming

namely

• Purity (a.k.a. immutability, eschewing side-effects, referential transparency)
• Higher-order functions (e.g. pass a function as a parameter, return it as a result, define anonymous function on the fly as a lambda expression)
• Laziness (a.k.a. non-strict evaluation, most useful/usable when coupled with purity)
• Algebraic data types and pattern matching
• Closures
• Currying / partial application
• Parametric polymorphism (a.k.a. generics)
• Recursion (more prominent as a result of purity)
• Programming with expressions rather than statements (again, from purity)

The more a particular programming language has syntax and constructs tailored to making the various FP features listed above easy/painless to express & implement, the more likely someone will label it a "functional language".