Granting the "everything is a function" idea the best intent, maybe
what it's trying to express is the related but different notion that
everything *can be* a function -- i.e. that any value can be replaced
by a function which yields a value of the appropriate type.
Alternately, it could be a confusion between the untyped lambda
calculus, in which everything really is a function, and the typed
lambda calculus, in which things are more complicated?
--S.
On Jan 2, 2009, at 2:53 PM, Conal Elliott wrote:
Hi Cristiano,
Similarly, any value can be thought of as a list (perhaps
singleton), a Maybe (Just), a pair ((,) undefined or (,) mempty),
an IO (return), ... (any Applicative).
And yet I've heard "everything is a function" on several occasions,
but not these others. Hence my (continuing) puzzlement about the
source of that idea. I have some speculations:
* In pure "OO" programming, everything is an object, so in pure
"functional" programming, one might assume everything is a
function. I find the term "value-oriented programming" a more
accurate label than "functional programming".
* C has definitions for functions but assignments for other types.
Since pure functional languages eliminate assignment, one might
assume that only functions remain. (I also hear people refer to
top-level definitions in a Haskell module as "functions", whether
they're of function type or not.)
Are there other thoughts & insights about the source of the idea
that "everything is a function"?
Thanks,
- Conal
On Fri, Jan 2, 2009 at 2:52 AM, Cristiano Paris
<fr...@theshire.org> wrote:
On Tue, Dec 30, 2008 at 8:35 AM, Conal Elliott <co...@conal.net>
wrote:
>> Everything in Haskell is a function [...]
>
> Where did this idea come from?
>
> I'd say every expression in Haskell denotes a pure value, only
some of which
> are functions (have type a->b for some types a & b).
Maybe more formally correct, but my statement still holds true as any
values can be tought as constant functions, even those representing
functions themselves.
Cristiano
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