[Robin_Message]

Firstly, using the preprocessor will mean there is code duplication, even if it is not necessary. Secondly, once you are using the preprocessor to do generic stuff, you have probably thrown type-safety away.

That's not to say you can't write C in a generic way, but "generic programming" means something specific to computer scientists and has certain prerequisites.

And you can't write functional code without a functional language, without building a functional language on top of your language (which may not even be possible, e.g. you can do functional-ish stuff in C because of function pointers. Without them, you'd be stuffed.)

You can write functional code in a "non functional language", if by functional language you mean "Haskell, ML or Scala". But you need certain features like function pointers to do it, and in that sense you do need a functional language. Same for generic programming - you need certain features.

[Raphael_Amiard]

Function pointers are very far from sufficient because you can't define new functions at runtime, since you can't nest functions or define anonymous ones. That means your functions are not first class citizen of your language and some common functional programming techniques are impossible to use in a clear way.

You can't do that for example :

    def make_adder(num_1):
        def adder(num_2):
            return num_1 + num 2
        return adder

[Robin_Message]

Yes. Generally you then start cheating by passing around a function pointer and a void* that is the first argument of the function, i.e. doing closure conversion yourself. You can hide this with some macros and get close to having a functional language, but it's ugly and tedious (Cfront anyone?) Also, what I'm describing here is more similar to object orientation than functional programming. It's worth remembering the following koan though:

The venerable master Qc Na was walking with his student, Anton. Hoping to prompt the master into a discussion, Anton said "Master, I have heard that objects are a very good thing - is this true?" Qc Na looked pityingly at his student and replied, "Foolish pupil - objects are merely a poor man's closures."

Chastised, Anton took his leave from his master and returned to his cell, intent on studying closures. He carefully read the entire "Lambda: The Ultimate..." series of papers and its cousins, and implemented a small Scheme interpreter with a closure-based object system. He learned much, and looked forward to informing his master of his progress.

On his next walk with Qc Na, Anton attempted to impress his master by saying "Master, I have diligently studied the matter, and now understand that objects are truly a poor man's closures." Qc Na responded by hitting Anton with his stick, saying "When will you learn? Closures are a poor man's object." At that moment, Anton became enlightened.

-- Anton van Straaten