Functional languages

There is no such thing as a functional language.

You can write functionally in any language.

Also, different languages have different functional features.

Functional features

Feature	C	C++	Haskell	Idris	Java	OCaml	Python	Rust	Scala
Closures	❌	⚠️	✔️	✔️		✔️	✔️	⚠️	✔️
Downwards Funarg Problem	✔️	✔️	✔️	✔️	✔️	✔️	✔️	✔️	✔️
Functions	✔️	✔️	✔️	✔️	✔️	✔️	✔️	✔️	✔️
Guaranteed Tail Call Optimization			✔️	✔️	❌	✔️			⚠️
Lambda Abstraction Syntax	❌	✔️	✔️	✔️	✔️	✔️	⚠️	✔️	✔️
Pure Functions	❌	⚠️	✔️	✔️	❌	❌	❌	❌	❌
Upwards Funarg Problem	❌	⚠️	✔️	✔️	✔️	✔️	✔️	✔️	✔️

Feature	C	C++	Haskell	Idris	Java	OCaml	Python	Rust	Scala
Ad Hoc Polymorphism	❌	✔️	✔️	✔️		✔️	✔️	✔️	✔️
Algebraic Data Types	❌	❌	✔️	✔️		✔️	❌	✔️	✔️
Dependent Types	❌	❌	❌	✔️		❌	❌	❌	❌
Forces Immutability	❌	❌	✔️	✔️		✔️	❌	✔️	⚠️
Immutable Data	❌	✔️	✔️	✔️		✔️	✔️	✔️	✔️
Laziness By Default	❌	❌	✔️	❌		❌	❌	❌	❌
Parametric Modules	❌	❌	⚠️	✔️		✔️	❌	❌	✔️
Parametric Polymorphism		✔️	✔️	✔️	✔️	✔️	✔️	✔️	✔️
Pattern Matching		⚠️	✔️	✔️		✔️	⚠️	⚠️	✔️
Pattern Matching Alternatives			✔️	✔️		✔️		✔️	✔️
Pattern Matching Variable Introduction			✔️	✔️			✔️	✔️	✔️
Polymorphic Recursion	❌	❌	✔️	✔️	❌	✔️	⚠️		✔️
Referential Transparency			✔️	✔️					❌
Row Polymorphism	❌	❌	⚠️		❌	✔️	❌
Static Typing	⚠️	✔️	✔️	✔️	✔️	✔️	❌	✔️	✔️
Totality Checking	❌	❌	❌	✔️		❌	❌	❌	❌
Uniqueness Types	❌	❌	❌	✔️		❌	❌	✔️	❌
Universe Polymorphism	❌	❌	❌	✔️		❌	❌	❌	❌

A well implemented feature counts as 1, a hard-to-use one counts as 0.5. Supporting featurues count twice less.