This is ONE nested function, not F1 >>? F2: Kim, This is a very useful insight (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. Also consider this: in Haskell, a function is a binding like any other. If you couldn't refer to bindings from outer scopes, you couldn't define new functions! Well, aside from anonymous ones/lambdas, which are useful but somewhat limiting if you can't name and reuse them. 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. 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. Thanks for your quick replies Divam On 29 December 2012 07:29, Brandon Allbery wrote:

On Fri, Dec 28, 2012 at 8:14 PM, Divam wrote:

...

Although this might be something very trivial but I am stuck here and not able to understand how this is working. (considering the functions to be pure they can only access values passed to them as input).

They can access any bindings in the same scope; since a lambda binding does not define a new scope in the same way a top level binding does, the earlier bindings are still in scope and accessible.

Consider this: a multi-parameter binding such as

\a b c -> a + b + c

is really the same thing as

\a -> (\b -> (\c -> a + b + c))

(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.

What you can't do in a pure function is *change* them; all bindings are read only, whether in or inward of their scope. Inward scopes can redefine bindings, but those new bindings are unrelated to the outer ones.

Also consider this: in Haskell, a function is a binding like any other. If you couldn't refer to bindings from outer scopes, you couldn't define new functions! Well, aside from anonymous ones/lambdas, which are useful but somewhat limiting if you can't name and reuse them.

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

Hi,

Brandon, I need to study this again, still dont understood how its related to partial function application.

Take a look at: http://learnyouahaskell.com/higher-order-functions#lambdas addThree :: (Num a) => a -> a -> a -> a addThree x y z = x + y + z can be defined as: addThree :: (Num a) => a -> a -> a -> a addThree = \x -> \y -> \z -> x + y + z and with brackets it would be: addThree = \x -> (\y -> (\z -> (x + y + z))) Now, you just need to put brackets to see what's going on there (i've simplified your code for clarity): t v = Just v >>? \v1 -> Just (v + 1) >>? \v2 -> Just (v + v1 + v2) This would be (it actually is!): t v = Just v >>? \v1 -> (Just (v + 1) >>? \v2 -> (Just (v + v1 + v2) ) ) Now, if you will put braces in wrong place: t v = Just v >>? (\v1 -> Just (v + 1)) >>? (\v2 -> Just (v + v1 + v2)) Then you will get: Not in scope: `v1'

Also consider this: in Haskell, a function is a binding like any other. If you couldn't refer to bindings from outer scopes, you couldn't define new functions! Well, aside from anonymous ones/lambdas, which are useful but somewhat limiting if you can't name and reuse them.

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.

These 'global expressions' do not change during execution, output is dependent only on input, and function could be defined in terms of arguments and some 'constants' ('global expressions') and other functions (also 'global expressions' (there is no difference). Emanuel