applicative Questions
2
Solved
I found this implementation of the average function:
avg :: [Int] -> Int
avg = div . sum <*> length
How does this work? I looked at the function that was produced as a result of div . sum...
Ohl asked 23/8, 2020 at 21:52
0
Despite the jargon filled title I don't think this question is very complex.
Introducing the characters
There are two important Functor combinators at play here. Flip equivalent to the haskell func...
Capsulize asked 23/8, 2020 at 2:55
3
Solved
In GHC.Base the description of <**> runs:
A variant of <*> with the arguments reversed.
It is widely known that "reversed" in that case does not mean "flipped" as:...
Pumphrey asked 31/7, 2020 at 11:7
3
Solved
I have learnt about Monoidal being an alternative way to represent Applicative not so long ago. There is an interesting question on Typeclassopedia:
(Tricky) Prove that given your implementations...
Idell asked 17/7, 2020 at 7:31
2
Solved
Two Main Problems to solve:
1) Type check is lost
Using the array argument Single.zip() version I lose the strongly typed arguments.
2) Source argument Cannot be Nullable
I cannot send nullable sou...
Highpressure asked 11/7, 2020 at 3:1
1
Solved
Related to this question https://stackoverflow.com/questions I want to achieve the same in Java with rxJava2 as in haskell How can I implement generalized "zipn" and "unzipn" in...
Yardmaster asked 14/7, 2020 at 4:40
5
Solved
Alternative, an extension of Applicative, declares empty, <|> and these two functions:
One or more:
some :: f a -> f [a]
Zero or more:
many :: f a -> f [a]
If defined, some...
Accentor asked 7/8, 2013 at 16:23
2
Given an operation (??) such that
(a ?? b) ?? c = a ?? (b ?? c)
(that is to say (??) is associative)
must it be the case that
liftA2 (??) (liftA2 (??) a b) c = liftA2 (??) a (liftA2 (??) b c)
...
Ceaseless asked 27/5, 2020 at 6:44
1
Solved
A few times now, I've found myself defining:
(<?>) :: [a] -> [a] -> [a]
[] <?> ys = ys
xs <?> _ = xs
This is an associative operation, of course, and the empty list [] is...
Him asked 17/5, 2020 at 23:27
2
Solved
I'm fairly new to Haskell and functional programming and I have recently been learning about Functors, Applicatives and Monads. While I seem to understand the basics, I have trouble figuring out th...
Fanechka asked 21/5, 2020 at 10:21
3
Solved
I’m trying to understand the applicative typeclass, and in particular the <*> function. Now I see its type signature is f (a -> b) -> f a -> f b and I take it that f is a functor, wh...
Grizzled asked 18/5, 2020 at 20:9
3
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Perhaps neither of these statements are categorically precise, but a monad is often defined as "a monoid in the category of endofunctors"; a Haskell Alternative is defined as "a monoid on applicati...
Catboat asked 24/4, 2018 at 18:46
1
There is ApplicativeError[F,E] + F[A] and there is Either[E, A]. Both convey the message that the function could fail with an E or succeed with an A but I'm not sure about the different message the...
Radicel asked 28/4, 2020 at 14:57
0
The Applicative instance for Data.Sequence generally performs very well. Almost all the methods are incrementally asymptotically optimal in time and space. That is, given fully forced/realized inpu...
Significancy asked 10/3, 2020 at 16:30
3
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The Applicative typeclass represents lax monoidal functors that preserve the cartesian monoidal structure on the category of typed functions.
In other words, given the canonical isomorphisms witne...
Adverb asked 9/3, 2020 at 7:16
4
Solved
Chapter 11 of Learn You a Haskell introduces the following definition:
instance Applicative ((->) r) where
pure x = (\_ -> x)
f <*> g = \x -> f x (g x)
Here, the author engages ...
Superaltar asked 4/8, 2012 at 18:7
2
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I'm learning Haskell's Applicatives. It seems to me (I'm probably wrong) that the pure function is not really needed, for example:
pure (+) <*> [1,2,3] <*> [3,4,5]
can be written as...
Mamiemamma asked 18/2, 2020 at 6:32
1
Solved
Here's the SO post I'm going to refer to. Also, I'm going to use the same snippets as the OP in that question in order not to separate the materials.
It is widely known that an ArrowApply instance ...
Trypsin asked 22/1, 2020 at 22:54
2
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After trying out examples for a while, to me it looks like myFunction <$> and pure myFunction <*> are equivalent when working on the Control.Applicative type class.
Example:
(++) <...
Ammon asked 13/1, 2020 at 14:17
1
The Naturality law states that:
t . traverse f == traverse (t . f) -- for every applicative transformer t
Now for the RHS of the law, if f has the type Applicative a => x -> a y, then t ha...
Zurek asked 24/11, 2019 at 17:2
3
Solved
In Haskell Applicatives are considered stronger than Functor that means we can define Functor using Applicative like
-- Functor
fmap :: (a -> b) -> f a -> f b
fmap f fa = pure f <*>...
Carilla asked 10/11, 2019 at 13:13
2
Solved
Consider this example:
{-# language ApplicativeDo #-}
module X where
data Tuple a b = Tuple a b deriving Show
instance Functor (Tuple a) where
fmap f (Tuple x y) = Tuple x (f y)
instance Fold...
Innocent asked 6/10, 2019 at 6:45
3
Solved
How can I properly prove that
sequenceA :: (Traversable t, Applicative f) => t (f a) -> f (t a)
sequenceA [] = pure []
sequenceA (x:xs) = pure (:) <*> x <*> sequenceA xs
is ess...
Elias asked 29/7, 2019 at 4:35
1
In Maybe applicative, <*> can be implemented based on fmap. Is it incidental, or can it be generalized to other applicative(s)?
(<*>) :: Maybe (a -> b) -> Maybe a -> Maybe b
N...
Matronna asked 26/7, 2019 at 12:43
1
Class Applicative is declared as:
class Functor f => Applicative f where
pure :: a -> f a
(<*>) :: f (a -> b) -> f a -> f b
We can represent fmapi, i=0,1,2,... in terms of p...
Obannon asked 24/7, 2019 at 17:31
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