Functional Programming History
The history of functional programming can be traced back to Lambda-calculus. It is a mathematical language invented by Alonzo in 1930. In some ways, lambda-calculus is the first programming language. Some principles of lambda calculus can be found in modern functional languages and even in Java also. The first principle is that the main object in this kind of language is functions and functions in the mathematical sense of these words. something that takes input and returns the output.
It always returns the same output if based on the same input. Hence, this property goes by the name of being stateless. In other words, the function has no memory of previous inputs.