, 9/4/10, David Menendez wrote:
From: David Menendez
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Saturday, September 4, 2010, 2:23 PM
On Sat, Sep 4, 2010 at 2:06 PM, michael rice wrote:
The two myAction functions below seem to be equiv
On Sat, Sep 4, 2010 at 2:06 PM, michael rice wrote:
> The two myAction functions below seem to be equivalent and, for this small
> case, show an interesting economy of code, but being far from a Haskell
> expert, I have to ask, is the first function as small (code wise) as it
> could be?
>
> Mich
The two myAction functions below seem to be equivalent and, for this small
case, show an interesting economy of code, but being far from a Haskell expert,
I have to ask, is the first function as small (code wise) as it could be?
Michael
import Control.Applicative
data Color
= Red
| Bl
Cool, I'll go looking for it. I couldn't find anything on Hoogle.
Thanks,
Michael
--- On Thu, 9/2/10, David Menendez wrote:
From: David Menendez
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Thursday, September 2, 2
On Thu, Sep 2, 2010 at 9:16 PM, michael rice wrote:
> This may be a dumb question, but here goes.
>
> Types Maybe, Either, List, are types and also instances of Functor (and
> Monad).
>
> Assuming (->) is also a type, where can I find its type definition?
>
(->) is a built-in type. You could say
This may be a dumb question, but here goes.
Types Maybe, Either, List, are types and also instances of Functor (and Monad).
Assuming (->) is also a type, where can I find its type definition?
Michael
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xander Solla wrote:
From: Alexander Solla
Subject: Re: [Haskell-cafe] On to applicative
To:
Cc: "haskell-cafe Cafe"
Date: Thursday, September 2, 2010, 2:46 PM
On Sep 2, 2010, at 11:30 AM, michael rice wrote:
In each case, what does the notation
show:: ...
and
undefined:: ...
ac
On Sep 2, 2010, at 11:30 AM, michael rice wrote:
In each case, what does the notation
show:: ...
and
undefined:: ...
accomplish?
They're type annotations. show is a function in "many" types:
Prelude> :t show
show :: (Show a) => a -> String
If you want to see the type of a "specific" sh
nt -> String
Michael
--- On Tue, 8/31/10, Ryan Ingram wrote:
From: Ryan Ingram
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: "Vo Minh Thu" , haskell-cafe@haskell.org
Date: Tuesday, August 31, 2010, 4:17 PM
FmapFunc is just a test module I c
On Thu, Sep 2, 2010 at 10:45 AM, michael rice wrote:
>
> Can you think of a situation for
>
> \x -> f x
> or
> \x y z -> x + ord y - head z
>
> that would require x (y z) to have their type(s) declared (ala Pascal), or
> is it always
> inferred by what appears to the right of "->"?
>
I think H
0, Tillmann Rendel wrote:
From: Tillmann Rendel
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Wednesday, September 1, 2010, 5:28 PM
michael rice wrote:
> Prelude Data.Either> let m = Just 7
> Prelude Data.Either> :t
t
Can you think of a situation for
\x -> f x
that would require x to have a declared type, or is it always inferred by the
type of f?
Michael
--- On Wed, 9/1/10, Tillmann Rendel wrote:
From: Tillmann Rendel
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice&qu
michael rice wrote:
Prelude Data.Either> let m = Just 7
Prelude Data.Either> :t m
m :: Maybe Integer
So to create a value of type (Maybe ...), you can use Just.
Prelude Data.Either> let l = 2:[]
Prelude Data.Either> :t l
l :: [Integer]
So to create a value of type [...], you can use (:) and
Thanks, Brandon, but Ryan gave me what I was looking for.
Michael
--- On Tue, 8/31/10, Brandon S Allbery KF8NH wrote:
From: Brandon S Allbery KF8NH
Subject: Re: [Haskell-cafe] On to applicative
To: haskell-cafe@haskell.org
Date: Tuesday, August 31, 2010, 4:35 PM
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On 8/31/10 13:27 , michael rice wrote:
> So it's a type constructor, not a type? Could you please provide a simple
> example of its usage?
Assuming you don't mean the trivial use in defining functions, see
Control.Monad.Instances:
> instance Functor
> *Main> :t (->) Int Char
>
> :1:1: parse error on input `->'
>
> What got loaded with FmapFunc? I Hoogled it and got back nothing.
>
> Michael
>
> --- On *Tue, 8/31/10, Ryan Ingram * wrote:
>
>
> From: Ryan Ingram
>
> Subject: Re: [Haskell-caf
hael
>
>
> --- On Tue, 8/31/10, Vo Minh Thu wrote:
>
> From: Vo Minh Thu
> Subject: Re: [Haskell-cafe] On to applicative
> To: "michael rice"
> Cc: "Ryan Ingram" , haskell-cafe@haskell.org
> Date: Tuesday, August 31, 2010, 3:23 PM
>
> 2010/8/3
om: Vo Minh Thu
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: "Ryan Ingram" , haskell-cafe@haskell.org
Date: Tuesday, August 31, 2010, 3:23 PM
2010/8/31 michael rice
>
> Hi Vo,
>
> Pardon, I grabbed the wrong lines.
>
> *Main>
On Aug 31, 2010, at 12:03 PM, michael rice wrote:
I tried creating an instance earlier but
*Main> :t (->) Int Char
:1:1: parse error on input `->'
Try:
Prelude> :info (->)
data (->) a b-- Defined in GHC.Prim
If you want type-information about values, use :t. If you want
informa
> Michael
>
> --- On Tue, 8/31/10, Vo Minh Thu wrote:
>
> From: Vo Minh Thu
> Subject: Re: [Haskell-cafe] On to applicative
> To: "michael rice"
> Cc: "Ryan Ingram" , haskell-cafe@haskell.org
> Date: Tuesday, August 31, 2010, 3:07 PM
>
> 201
Hi Vo,
Pardon, I grabbed the wrong lines.
*Main> :t (->) 3 "abc"
:1:1: parse error on input `->'
Michael
--- On Tue, 8/31/10, Vo Minh Thu wrote:
From: Vo Minh Thu
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: "Ryan Ingram&qu
:t undefined :: Int
is ok, just like
:t undefined :: (->) Int Int
> What got loaded with FmapFunc? I Hoogled it and got back nothing.
>
> Michael
>
> --- On Tue, 8/31/10, Ryan Ingram wrote:
>
> From: Ryan Ingram
> Subject: Re: [Haskell-cafe] On to applicative
> To: &quo
wrote:
From: Ryan Ingram
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: "Vo Minh Thu" , haskell-cafe@haskell.org
Date: Tuesday, August 31, 2010, 2:36 PM
Prelude FmapFunc> let s = show :: ((->) Int) String
Prelude FmapFunc> :t s
s :: Int ->
nstance Functor Maybe where ...
Note how the type argument of Maybe is not given.
But above, when you create a value, it has type Maybe Int, not only Maybe.
So for the ((->) r) case, you still want to "complete" it.
E.g.
m :: Maybe Int -- not just Maybe
(+) :: (->) Int Int -
; :t e
> e :: Either a [Char]
>
> All these instances are functors, each with its own version of fmap that
> can be applied to it.
>
> How can I similarly create an instance of (->) so I can apply (->)'s
> version of fmap
>
> instance Functor ((->) r) whe
be
applied to it.
How can I similarly create an instance of (->) so I can apply (->)'s version of
fmap
instance Functor ((->) r) where
fmap f g = (\x -> f (g x))
to it?
Michael
--- On Tue, 8/31/10, Vo Minh Thu wrote:
From: Vo Minh Thu
Subject: Re: [Haskell-cafe] On to
> From: Vo Minh Thu
> Subject: Re: [Haskell-cafe] On to applicative
> To: "michael rice"
> Cc: haskell-cafe@haskell.org
> Date: Tuesday, August 31, 2010, 1:17 PM
>
> 2010/8/31 michael rice
> >
> > "Learn You a Haskell ..." says that (->
h Thu wrote:
> From: Vo Minh Thu
> Subject: Re: [Haskell-cafe] On to applicative
> To: "michael rice"
> Cc: haskell-cafe@haskell.org
> Date: Tuesday, August 31, 2010, 1:17 PM
> 2010/8/31 michael rice
>>
>> "Learn You a Haskell ..." says tha
So it's a type constructor, not a type? Could you please provide a simple
example of its usage?
Michael
--- On Tue, 8/31/10, Vo Minh Thu wrote:
From: Vo Minh Thu
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Tuesday, Aug
2010/8/31 michael rice
>
> "Learn You a Haskell ..." says that (->) is a type just like Either. Where
> can I find its type definition?
You can't define it *in* Haskell as user code. It is a built-in infix
type constructor (Either or Maybe are type constructors too, not just
types). In fact, if
"Learn You a Haskell ..." says that (->) is a type just like Either. Where can
I find its type definition?
Michael
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On 30 August 2010 14:50, michael rice wrote:
>
> Hi Ivan,
>
> I already looked there and didn't find anything, but went back and noticed
> the "Source Code" at the top right of the page and found it there. Why are
> there two source codes, the one at the top and the ones down the right margin
>
ael
--- On Mon, 8/30/10, Ivan Lazar Miljenovic wrote:
From: Ivan Lazar Miljenovic
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org, "Brandon S Allbery KF8NH"
Date: Monday, August 30, 2010, 12:36 AM
On 30 August 2010 14:25, mich
On 30 August 2010 14:25, michael rice wrote:
>
> Looks like the fmap definition for the Either functor matches what's given in
> Learn You A Haskell ...
>
> instance Functor (Either a) where
> fmap f (Right x) = Right (f x)
> fmap f (Left x) = Left x
>
> but Hoogle couldn't find Control.Mon
Control.Monad.Instances Data.Either> fmap length r
Right 4
--- On Sat, 8/28/10, Brandon S Allbery KF8NH wrote:
From: Brandon S Allbery KF8NH
Subject: Re: [Haskell-cafe] On to applicative
To: haskell-cafe@haskell.org
Date: Saturday, August 28, 2010, 9:06 PM
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On 29 August 2010 07:58, Ivan Lazar Miljenovic
wrote:
> One might also say that that's because there is no BiFunctor in the
> report, standard library, etc.
Yep - that's where the historical accident comes in.
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On 29 August 2010 16:51, Stephen Tetley wrote:
> One might also say its a historical accident that Either isn't an
> instance of Bifunctor - "Equal rights for Lefts!", but that's another
> story...
One might also say that that's because there is no BiFunctor in the
report, standard library, etc.
On 29 August 2010 02:06, Brandon S Allbery KF8NH wrote:
> -BEGIN PGP SIGNED MESSAGE-
> Hash: SHA1
>
> On 8/28/10 20:43 , michael rice wrote:
> Historical accident, to wit: Haskell 98 minimally defined Either in the
> Prelude, so in practice we get the basic definitions (Either itself and
Thanks, Brandon.
Michael
--- On Sat, 8/28/10, Brandon S Allbery KF8NH wrote:
From: Brandon S Allbery KF8NH
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Saturday, August 28, 2010, 10:43 PM
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On 8/28/10 22:15 , michael rice wrote:
> Prelude> fmap (*2) l
>
> :1:0:
> No instance for (Functor (Either Integer))
> arising from a use of `fmap' at :1:0-10
> Possible fix:
> add an instance declaration for (Functor (Either Integ
KF8NH wrote:
From: Brandon S Allbery KF8NH
Subject: Re: [Haskell-cafe] On to applicative
To: haskell-cafe@haskell.org
Date: Saturday, August 28, 2010, 9:06 PM
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On 8/28/10 20:43 , michael rice wrote:
> I'm looking at a discussion of Either (as f
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On 8/28/10 20:43 , michael rice wrote:
> I'm looking at a discussion of Either (as functor) here:
>
> http://learnyouahaskell.com/making-our-own-types-and-typeclasses#the-functor-typeclass
>
> instance Functor (Either a) where
> fmap f (Right x
I'm looking at a discussion of Either (as functor) here:
http://learnyouahaskell.com/making-our-own-types-and-typeclasses#the-functor-typeclass
instance Functor (Either a) where
fmap f (Right x) = Right (f x)
fmap f (Left x) = Left x
And this line in Data.Either
Functor (Either a)
A "map" can be a function (applied to a (single) value).
Got it.
Thanks,
Michael
--- On Fri, 8/27/10, Ivan Lazar Miljenovic wrote:
From: Ivan Lazar Miljenovic
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Friday, A
On 28 August 2010 10:38, michael rice wrote:
>
> fmap seems oddly named because no "mapping" takes place, except in the fourth
> example, where the map is "passed in." Just sayin'.
*ahem* http://en.wikipedia.org/wiki/Map_%28mathematics%29
> Prelude Control.Monad Control.Applicative Data.Char> f
fmap seems oddly named because no "mapping" takes place, except in the fourth
example, where the map is "passed in." Just sayin'.
Michael
1)
Prelude Control.Monad Control.Applicative> fmap (++ "abc") getLine
xyz
"xyzabc"
2)
Prelude Control.Monad Control.Applicative Data.Char Data.String> fmap (
some time there but will no doubt be back
before long with another question.
Thanks all,
Michael
--- On Thu, 8/26/10, Alexander Solla wrote:
From: Alexander Solla
Subject: Re: [Haskell-cafe] On to applicative
To:
Cc: "haskell-cafe Cafe"
Date: Thursday, August 26, 2010, 2:15 PM
O
On Aug 26, 2010, at 9:27 AM, michael rice wrote:
Some functions just happen to map to other functions.
<$> is flip fmap. f <$> functor = fmap f functor Brent
Yorgey's post noted.
"map to"? Take as arguments?
"maps to" as in "outputs".
pure f <*> functor = f <$> functor
Hi Alexander,
Didn't get to sleep till 4 AM and it took me a while to go though your post.
So far...
--- On Thu, 8/26/10, Alexander Solla wrote:
From: Alexander Solla
Subject: Re: [Haskell-cafe] On to applicative
To:
Cc: "haskell-cafe Cafe"
Date: Thursday, August 26, 2010, 4
On Thu, Aug 26, 2010 at 01:29:16AM -0700, Alexander Solla wrote:
>
>
> <$> is flip fmap. f <$> functor = fmap f functor
>
Just a quick correction: <$> is fmap, not flip fmap.
-Brent
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On Aug 26, 2010, at 1:29 AM, Alexander Solla wrote:
The other function is pure :: (a -> b) -> f (a -> b). It takes a
function and lifts it into the functor, without applying it to
anything. In other words, given an f :: a -> b,
My mistake, though if you got the rest of it, it should come
On Aug 26, 2010, at 12:34 AM, michael rice wrote:
A lot of stuff to get one's head around. Was aware of liftM2,
liftM3, etc., but not liftA2, liftA3, etc.
liftM and liftA are essentially equivalent (and are both essentially
equivalent to fmap) Same for the liftAn = liftMn functions (whe
e the patience.
Michael
--- On Thu, 8/26/10, Thomas Davie wrote:
From: Thomas Davie
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: "Ivan Lazar Miljenovic" ,
haskell-cafe@haskell.org
Date: Thursday, August 26, 2010, 3:10 AM
On 26 Aug 2010, at 08:01
On 26 Aug 2010, at 08:01, michael rice wrote:
> Hmm... it was my understanding that the example was showing how to *avoid*
> having to create a lot of functions that do the same thing but have
> different numbers of arguments.
>
> From the Wiki page:
>
> "Anytime you feel the need to define
t; Michael
>
>
>
> --- On Thu, 8/26/10, Ivan Lazar Miljenovic wrote:
>
> From: Ivan Lazar Miljenovic
> Subject: Re: [Haskell-cafe] On to applicative
> To: "michael rice"
> Cc: haskell-cafe@haskell.org
> Date: Thursday, August 26, 2010, 2:50 AM
>
>
date for function-arguments with a different number of arguments,
think about how defining a proper instance of Applicative can make your life
easier."
Not so?
Michael
--- On Thu, 8/26/10, Ivan Lazar Miljenovic wrote:
From: Ivan Lazar Miljenovic
Subject: Re: [Haskell-cafe] On to applicative
-> b' against inferred type `Int'
> In the first argument of `fmap3', namely `sumsqr'
> In the expression: fmap3 sumsqr (Just 3) (Just 4) (Just 5)
> In the definition of `it':
> it = fmap3 sumsqr (Just 3) (Just 4) (Just 5)
> *Main>
&g
(Just 5)
> In the definition of `it':
> it = fmap3 sumsqr (Just 3) (Just 4) (Just 5)
> *Main>
sumsqr takes three arguments; fmap3 has type:
fmap3 :: (a -> b -> c -> d) -> Maybe a -> Maybe b -> Maybe c -> Maybe d
i.e. the function you pass it needs
`fmap3', namely `sumsqr'
In the expression: fmap3 sumsqr (Just 3) (Just 4) (Just 5)
In the definition of `it':
it = fmap3 sumsqr (Just 3) (Just 4) (Just 5)
*Main>
--- On Thu, 8/26/10, Ivan Lazar Miljenovic wrote:
From: Ivan Lazar Miljenovic
Subject: Re:
On 26 August 2010 16:29, michael rice wrote:
>
> Can you recommend an example that works?
An example of what?
The definitions of fmap2, etc. on that page look like they're correct.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
__
Can you recommend an example that works?
Michael
--- On Thu, 8/26/10, Ivan Lazar Miljenovic wrote:
From: Ivan Lazar Miljenovic
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Thursday, August 26, 2010, 2:13 AM
On 26 August
On 26 August 2010 16:09, michael rice wrote:
>
> Yeah, I figured as much, but the code is copied right off the referenced page.
Because as Vo Minh Thu says, it was there as a demonstration; in this
instance they were doing "algebraic" manipulation of the code and
corresponding type signatures. A
Yeah, I figured as much, but the code is copied right off the referenced page.
Michael
--- On Thu, 8/26/10, Ivan Lazar Miljenovic wrote:
From: Ivan Lazar Miljenovic
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice"
Cc: haskell-cafe@haskell.org
Date: Thursday, Augus
2010/8/26 michael rice
>
> From: http://en.wikibooks.org/wiki/Haskell/Applicative_Functors
>
> =
> import Control.Applicative
>
> f :: (a -> b -> c)
> fmap :: Functor f => (d -> e) -> f d -> f e
> fmap f :: Functor f => f a -> f (b -> c) -- Identify d with a, and e w
On 26 August 2010 15:56, michael rice wrote:
>
> From: http://en.wikibooks.org/wiki/Haskell/Applicative_Functors
>
> =
> import Control.Applicative
>
> f :: (a -> b -> c)
> fmap :: Functor f => (d -> e) -> f d -> f e
> fmap f :: Functor f => f a -> f (b -> c) -- Iden
From: http://en.wikibooks.org/wiki/Haskell/Applicative_Functors
=
import Control.Applicative
f :: (a -> b -> c)
fmap :: Functor f => (d -> e) -> f d -> f e
fmap f :: Functor f => f a -> f (b -> c) -- Identify d with a, and e with (b
-> c)
sumsqr :: Int -> Int -> I
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