Re: [Haskell-cafe] need help with understanding expression

16 Nov 2012

      Sorry wrong paste

Prelude> :t 3 2
3 2 :: (Num a, Num (a -> t)) => t

What does the type mean in plain english?

Daryoush

On Fri, Nov 16, 2012 at 12:00 AM, Daryoush Mehrtash wrote:
...
Yes, same problem, and again I have no idea how to read the type
Prelude> :t max. 3 2
max. 3 2 :: (Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b
What does the type mean in plain english?
Daryoush
On Thu, Nov 15, 2012 at 11:56 PM, Ramana Kumar wrote:
...
Another experiment may be revealing:
:t 3 2
On Fri, Nov 16, 2012 at 7:46 AM, Daryoush Mehrtash wrote:
...
I see the point with :t (.)  that
max.(+1) 2 2
is the same as
max. 3 2
Which is not what I want.
But I have no idea what the type signature of this expression mean now
Prelude> :t max. 3 2
max. 3 2 :: (Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b
Any idea?
Daryoush
On Thu, Nov 15, 2012 at 11:19 PM, Ramana Kumar <
Ramana.Kumar@cl.cam.ac.uk> wrote:
...
Hi Daryoush,
I recommend you try these experiments first, and then reply back if
you're still confused.
:t max
:t (+1)
:t max . (+1)
:t (+1) 2
:t (.)
On Fri, Nov 16, 2012 at 7:10 AM, Daryoush Mehrtash 
...
wrote:
...
I am having hard time understanding how removing the
 outer parenthesis in
(max.(+1)) 2 2
to
max.(+1) 2 2
changes the meaning of expression.
My expectation was that "max.(+1) takes two numbers and returns the
max as defined in the type:
:t max.(+1)
max.(+1) :: (Ord b, Num b) => b -> b -> b
With parenthesis it does what I expect it to:
Prelude> :t (max.(+1)) 2 2
(max.(+1)) 2 2 :: (Ord b, Num b) => b
Prelude>  (max.(+1)) 2 2
3
But if I remove the parenthesis I get a beast that I have no idea what
its type signature mean any more
Prelude> :t (max.(+1)) 2 2
(max.(+1)) 2 2 :: (Ord b, Num b) => b
Prelude> :t max.(+1) 2 2
max.(+1) 2 2 :: (Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b
How did removal of parenthesis changed the meaning?      How do you
interpret the type:  "(Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b"?
Thanks
--
Daryoush
Weblog:  http://onfp.blogspot.com/
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--
Daryoush
Weblog:  http://onfp.blogspot.com/
--
Daryoush
Weblog:  http://onfp.blogspot.com/
-- 
Daryoush

Weblog:  http://onfp.blogspot.com/