[Haskell-beginners] Re: Closure

Daniel Bastos dbastos+0 at toledo.com
Sat Aug 15 12:07:08 EDT 2009

In article <h65p0h$rjl$1 at ger.gmane.org>,
Heinrich Apfelmus wrote:

> The simplest example of a closure is indeed
>    foo = add 3
> where
>    add = \x y -> x + y

Question. This is actually equal to 

add x y = x + y

But you wrote in terms of \. Why such preference?

> Reduction to weak head normal form yields
>    foo = let x = 3 in \y -> x + y
> which means that  foo  is a function  \y -> x + y  paired with the value
> of the free variable  x .

I see.

> Note that closures are an implementation detail. From a semantic point
> of view,  add 3  can readily be understood as an ordinary function.

This makes sense. Because, even in a language like C, a similar effect
can be achieved, no? For example

int plus(int x, int y) { return x + y; }

int plus3(int y) { plus(3, y); }

So, what I can't do in C, besides almost everything I can't do, is to
do this nicely like I do in Haskell. But we don't call this a
closure. In fact, we say C does not allow for closures. So what am I

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