[Haskell-beginners] Value access in lambda function

[Brandon Allbery]

On Fri, Dec 28, 2012 at 10:57 PM, Divam <dfordivam at gmail.com> wrote:

> (This is, in fact, how partial function application works.)  a is still in
> scope when b is defined, a and b are still in scope when c is defined.
>
> Brandon, I need to study this again, still dont understood how its related
> to partial function application.
>

A function of multiple arguments is actually a function of a single
argument which returns a function that takes the next argument, and so on.
 Partial application therefore happens automatically.


> Brandon, This is quite strange thing, the functions can access the
> globally defined variables and therefore there output is dependent not just
> on inputs but on those variables too. This goes against the understanding
> of pure functions.
>

You may be using a different definition of "pure" than Haskell does; the
point of pure functions in Haskell is that they cannot *change* anything
outside of the function scope, not that they can't *see* anything.


> Also there may be  another way to look at this - all the global variables
> are inputs to all the functions. I think this is how the haskell looks at
> this scenario.
>

There are no variables involved.  "Variables" can vary; bindings are
immutable.  This is key to purity.

-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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