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Today's Topics:
1. Re: Change in type that I don't understand (David McBride)
2. Re: Change in type that I don't understand (Daniel Trstenjak)
3. Re: Change in type that I don't understand (David McBride)
4. Re: Change in type that I don't understand (David McBride)
5. Re: Change in type that I don't understand (Daniel Trstenjak)
6. applicative instance (sasa bogicevic)
7. Re: applicative instance (Benjamin Edwards)
----------------------------------------------------------------------
Message: 1
Date: Fri, 27 Jan 2017 08:35:08 -0500
From: David McBride <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Change in type that I don't
understand
Message-ID:
<can+tr42qgsgmdos5g7arvfayn+m8shthx4mff31-pehj9nl...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
If you have the Monomorphism restriction set, it will choose types
based on the type defaulting rules (Num changes to Integer). This is
because polymorphic code is slower than code that has concrete types.
Try :set -XNoMonomorphismRestriction, then test it again.
It may be that different versions of ghci have a different default for
that pragma.
On Fri, Jan 27, 2017 at 6:23 AM, Jan Erik Moström <[email protected]> wrote:
> Hi,
>
> Here is something that I don't understand, why does the named value have a
> different type than just the value itself?
>
> Prelude> let f x = x * x
> Prelude> :t f
> f :: Num a => a -> a
> Prelude> :t [f]
> [f] :: Num a => [a -> a]
> Prelude> let g = [f]
> Prelude> :t g
> g :: [Integer -> Integer]
>
> = jem
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
Message: 2
Date: Fri, 27 Jan 2017 16:17:48 +0100
From: Daniel Trstenjak <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Change in type that I don't
understand
Message-ID: <20170127151748.GA9028@octa>
Content-Type: text/plain; charset=us-ascii
On Fri, Jan 27, 2017 at 08:35:08AM -0500, David McBride wrote:
> If you have the Monomorphism restriction set, it will choose types
> based on the type defaulting rules (Num changes to Integer). This is
> because polymorphic code is slower than code that has concrete types.
But why didn't the defaulting rules have been applied for both: 'f' and 'g'?
Greetings,
Daniel
------------------------------
Message: 3
Date: Fri, 27 Jan 2017 10:43:28 -0500
From: David McBride <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Change in type that I don't
understand
Message-ID:
<CAN+Tr43JsxKjf5R5yEWYTBu_MCN2RXbmHJDRhtC=kge5ock...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Because f has an argument x, and g doesn't.
On Fri, Jan 27, 2017 at 10:17 AM, Daniel Trstenjak
<[email protected]> wrote:
>
> On Fri, Jan 27, 2017 at 08:35:08AM -0500, David McBride wrote:
>> If you have the Monomorphism restriction set, it will choose types
>> based on the type defaulting rules (Num changes to Integer). This is
>> because polymorphic code is slower than code that has concrete types.
>
> But why didn't the defaulting rules have been applied for both: 'f' and 'g'?
>
> Greetings,
> Daniel
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
Message: 4
Date: Fri, 27 Jan 2017 10:53:47 -0500
From: David McBride <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Change in type that I don't
understand
Message-ID:
<can+tr422twzxrhmiwc2cctmisuk0_309ncampv9i9devvea...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Sorry let me elaborate. The type of f depends on its argument. The
argument could be anything that the caller passes in so long as it is
an instance of Num. If the user passes in Int or Integer or Float, it
has to handle all those cases. It can't just type restrict the
argument to Int, that is likely not what the user wanted. If he had
he would have type restricted it himself.
g on the other hand has complete control over its own type. If mm
restriction is enabled and there is no type declaration then it is
reasonable for it to default to a concrete type so that it only has to
generate only one possible code path.
If it isn't enabled then it will try to be as polymorphic as possible,
at the cost of being flexible enough to return any type that is an
instance of Num.
On Fri, Jan 27, 2017 at 10:17 AM, Daniel Trstenjak
<[email protected]> wrote:
>
> On Fri, Jan 27, 2017 at 08:35:08AM -0500, David McBride wrote:
>> If you have the Monomorphism restriction set, it will choose types
>> based on the type defaulting rules (Num changes to Integer). This is
>> because polymorphic code is slower than code that has concrete types.
>
> But why didn't the defaulting rules have been applied for both: 'f' and 'g'?
>
> Greetings,
> Daniel
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
Message: 5
Date: Fri, 27 Jan 2017 17:29:09 +0100
From: Daniel Trstenjak <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Change in type that I don't
understand
Message-ID: <20170127162909.GB11209@octa>
Content-Type: text/plain; charset=us-ascii
Thank you for the nice explanation!
Greetings,
Daniel
------------------------------
Message: 6
Date: Fri, 27 Jan 2017 23:09:07 +0100
From: sasa bogicevic <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] applicative instance
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
What is wrong with my applicative instance for custom List type ?
http://lpaste.net/351723
data List a = Nil | Cons a (List a) deriving (Eq, Show)
instance Applicative List where
pure x = Cons x Nil
Nil <*> _ = Nil
_ <*> Nil = Nil
(Cons x xy) <*> (Cons z dy) = Cons (x z) (xy <*> dy)
Prelude> let functions = Cons (+1) (Cons (*2) Nil)
Prelude> let values = Cons 1 (Cons 2 Nil)
Prelude> functions <*> values
Cons 2 (Cons 3 (Cons 2 (Cons 4 Nil))) -- I get Cons 2 (Cons 4 Nil) what is
wrong with my Applicative instance ?
{
name: Bogicevic Sasa
phone: +381606006200
}
------------------------------
Message: 7
Date: Fri, 27 Jan 2017 22:17:35 +0000
From: Benjamin Edwards <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] applicative instance
Message-ID:
<CAN6k4nhYfCKyp327A0uJqqQXbb39iCCpAi1gMZsOPk=-p5c...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
You are zipping rather than taking the cross product.
Ben
On Fri, 27 Jan 2017, 22:09 sasa bogicevic, <[email protected]> wrote:
> What is wrong with my applicative instance for custom List type ?
>
> http://lpaste.net/351723
>
> data List a = Nil | Cons a (List a) deriving (Eq, Show)
>
>
>
> instance Applicative List where
> pure x = Cons x Nil
> Nil <*> _ = Nil
> _ <*> Nil = Nil
> (Cons x xy) <*> (Cons z dy) = Cons (x z) (xy <*> dy)
>
> Prelude> let functions = Cons (+1) (Cons (*2) Nil)
> Prelude> let values = Cons 1 (Cons 2 Nil)
> Prelude> functions <*> values
> Cons 2 (Cons 3 (Cons 2 (Cons 4 Nil))) -- I get Cons 2 (Cons 4 Nil) what
> is wrong with my Applicative instance ?
>
>
> {
> name: Bogicevic Sasa
> phone: +381606006200
> }
>
>
>
> _______________________________________________
> Beginners mailing list
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