[cryptonector]

Perhaps I should have written "imperative" rather than "procedural", except no one really writes imperative non-procedural code now.

> Also, “procedural” (or “imperative” or “functional”) is an attribute of programming languages, not applications/systems:

It can be an attribute of programs regardless of language. It is possible to write functional-style code in C and procedural code in Haskell (just do everything in the IO monad!).

> Haskell is a pure functional programming languages, in which evaluating functions has no side effects, but it can define systems that have effects.

That's a bit of a fiction. Pure functions are pure, yes, but you can have impure functions -- Haskell is only interesting because you can have impure functions (otherwise every Haskell program would compile down into a constant), and what's really interesting about Haskell is the ideas that have evolved in its community about how to deal with impure functions.

[dragonwriter]

> Pure functions are pure, yes, but you can have impure functions

Not in Haskell, you can't.

> Haskell is only interesting because you can have impure functions

No, it's interesting because it provides a way of representing series of effectful operations that are distinct from its functions, which are pure.

> otherwise every Haskell program would compile down into a constant

Every program in any language that is compiled compiles down to a constant (which is, itself, usually a program, often an imperative one in a native or virtual machine language); but in Haskell, each program is (in the model of the language, not merely what they compile to) normally a constant, non-function expression, most commonly of type IO ().

It's true that values of type IO a are isomorphic to “impure nullary functions returning a” in a language which has impure functions, but they aren't functions in Haskell, and can't be called from functions, they can only be operated on as values within the language.

[cryptonector]

Haskell's effectful operations are functions. Oh sure, not in the mathematical sense unless you model them as functions from World -> World.

> Every program in any language that is compiled compiles down to a constant ...

Sigh, yes, the compiled program is constant, but you know what I meant: a constant value, such as a number, that the program is expected to output. Let's not be this pedantic.

[dragonwriter]

> Haskell's effectful operations are functions.

No, they aren't.

> Oh sure, not in the mathematical sense unless you model them as functions from World -> World.

Also, not in the syntactical sense.

They are “functions” in that “in certain other programming languages, the closest thing to something filling the same role are called ’functions’.”

But it's rather important to the way Haskell works that they are a different thing that operate at a logically different time, than functions.

> Sigh, yes, the compiled program is constant, but you know what I meant

Yes, you meant reduction, not compilation, and you meant non-function, not just constant, but Haskell programs do reduce to non-function constants.