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Today's Topics:
1. help understanding error from attempt at CIS 194 : Homework
7 - indexJ (Dustin Lee)
2. Re: help understanding error from attempt at CIS 194 :
Homework 7 - indexJ (divyanshu ranjan)
3. Re: help understanding error from attempt at CIS 194 :
Homework 7 - indexJ (Dustin Lee)
----------------------------------------------------------------------
Message: 1
Date: Thu, 8 Jan 2015 12:01:49 -0700
From: Dustin Lee <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] help understanding error from attempt at
CIS 194 : Homework 7 - indexJ
Message-ID:
<CAN3sYc34mh5=3ilravejn1urq2qujqafmeucd0lz+v6dtpv...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Here's what I have so far for JoinList.hs: (
http://www.seas.upenn.edu/~cis194/spring13/hw/07-folds-monoids.pdf)
====
module JoinList
where
import Data.Monoid
import Sized
data JoinList m a = Empty
| Single m a
| Append m (JoinList m a) (JoinList m a)
deriving (Eq, Show)
tag :: Monoid m => JoinList m a -> m
tag Empty = mempty
tag (Single m a) = m
tag (Append m _ _) = m
(+++) :: Monoid m => JoinList m a -> JoinList m a -> JoinList m a
(+++) x y = Append (tag x <> tag y) x y
indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
indexJ _ Empty = Nothing
indexJ i (Single m a)
| i == 0 = Just a
| otherwise = Nothing
indexJ i (Append m x y)
| (getSize (tag x)) >= i = indexJ i x
| otherwise = indexJ (i - (getSize (tag x))) y
=====
Here is the error I'm getting. Haven't been able to make sense of it yet.
*Sized> :load "JoinList.hs"
[1 of 2] Compiling Sized ( Sized.hs, interpreted )
[2 of 2] Compiling JoinList ( JoinList.hs, interpreted )
JoinList.hs:50:21:
Could not deduce (b ~ Size)
from the context (Sized b, Monoid b)
bound by the type signature for
indexJ :: (Sized b, Monoid b) => Int -> JoinList b a ->
Maybe a
at JoinList.hs:44:11-63
`b' is a rigid type variable bound by
the type signature for
indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
at JoinList.hs:44:11
Expected type: JoinList Size a
Actual type: JoinList b a
In the first argument of `tag', namely `x'
In the first argument of `getSize', namely `(tag x)'
In the first argument of `(>=)', namely `(getSize (tag x))'
Failed, modules loaded: Sized.
thanks!
--
Dustin Lee
qhfgva=rot13(dustin)
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Message: 2
Date: Fri, 9 Jan 2015 00:56:44 +0530
From: divyanshu ranjan <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] help understanding error from attempt
at CIS 194 : Homework 7 - indexJ
Message-ID:
<CAL9hw259N4t7S=vaTytOkgoVJ=VjrbuLJp=566csyc0wgmp...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi Dustin,
(tag x) return something of type b which implements Sized and Monoid.
Where as getSize takes value of type Size.
Hence the error. b might not be equal to Size. Thus compiler is
complaining.
Given b is (Sized b), how one can convert it into Size ?
Thanks
Divyanshu Ranjan
On Fri, Jan 9, 2015 at 12:31 AM, Dustin Lee <[email protected]> wrote:
> Here's what I have so far for JoinList.hs: (
> http://www.seas.upenn.edu/~cis194/spring13/hw/07-folds-monoids.pdf)
>
> ====
> module JoinList
>
> where
>
> import Data.Monoid
> import Sized
>
> data JoinList m a = Empty
> | Single m a
> | Append m (JoinList m a) (JoinList m a)
> deriving (Eq, Show)
>
>
> tag :: Monoid m => JoinList m a -> m
> tag Empty = mempty
> tag (Single m a) = m
> tag (Append m _ _) = m
>
> (+++) :: Monoid m => JoinList m a -> JoinList m a -> JoinList m a
> (+++) x y = Append (tag x <> tag y) x y
>
>
> indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
> indexJ _ Empty = Nothing
> indexJ i (Single m a)
> | i == 0 = Just a
> | otherwise = Nothing
> indexJ i (Append m x y)
> | (getSize (tag x)) >= i = indexJ i x
> | otherwise = indexJ (i - (getSize (tag x))) y
>
> =====
>
> Here is the error I'm getting. Haven't been able to make sense of it yet.
>
> *Sized> :load "JoinList.hs"
> [1 of 2] Compiling Sized ( Sized.hs, interpreted )
> [2 of 2] Compiling JoinList ( JoinList.hs, interpreted )
>
> JoinList.hs:50:21:
> Could not deduce (b ~ Size)
> from the context (Sized b, Monoid b)
> bound by the type signature for
> indexJ :: (Sized b, Monoid b) => Int -> JoinList b a ->
> Maybe a
> at JoinList.hs:44:11-63
> `b' is a rigid type variable bound by
> the type signature for
> indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
> at JoinList.hs:44:11
> Expected type: JoinList Size a
> Actual type: JoinList b a
> In the first argument of `tag', namely `x'
> In the first argument of `getSize', namely `(tag x)'
> In the first argument of `(>=)', namely `(getSize (tag x))'
> Failed, modules loaded: Sized.
>
>
>
> thanks!
>
> --
> Dustin Lee
> qhfgva=rot13(dustin)
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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------------------------------
Message: 3
Date: Thu, 8 Jan 2015 12:32:46 -0700
From: Dustin Lee <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] help understanding error from attempt
at CIS 194 : Homework 7 - indexJ
Message-ID:
<CAN3sYc1UpLQr=ahvnEDeDsZMfrJ13346bzzMOjLgM=zrhtb...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Ahhh.... I'm using the size function now and at least I don't get any
compile errors anymore..... Now to check the code actually works.
Thanks!
On Thu, Jan 8, 2015 at 12:26 PM, divyanshu ranjan <
[email protected]> wrote:
> Hi Dustin,
>
> (tag x) return something of type b which implements Sized and Monoid.
> Where as getSize takes value of type Size.
> Hence the error. b might not be equal to Size. Thus compiler is
> complaining.
>
> Given b is (Sized b), how one can convert it into Size ?
>
>
>
> Thanks
> Divyanshu Ranjan
>
>
> On Fri, Jan 9, 2015 at 12:31 AM, Dustin Lee <[email protected]> wrote:
>
>> Here's what I have so far for JoinList.hs: (
>> http://www.seas.upenn.edu/~cis194/spring13/hw/07-folds-monoids.pdf)
>>
>> ====
>> module JoinList
>>
>> where
>>
>> import Data.Monoid
>> import Sized
>>
>> data JoinList m a = Empty
>> | Single m a
>> | Append m (JoinList m a) (JoinList m a)
>> deriving (Eq, Show)
>>
>>
>> tag :: Monoid m => JoinList m a -> m
>> tag Empty = mempty
>> tag (Single m a) = m
>> tag (Append m _ _) = m
>>
>> (+++) :: Monoid m => JoinList m a -> JoinList m a -> JoinList m a
>> (+++) x y = Append (tag x <> tag y) x y
>>
>>
>> indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe a
>> indexJ _ Empty = Nothing
>> indexJ i (Single m a)
>> | i == 0 = Just a
>> | otherwise = Nothing
>> indexJ i (Append m x y)
>> | (getSize (tag x)) >= i = indexJ i x
>> | otherwise = indexJ (i - (getSize (tag x))) y
>>
>> =====
>>
>> Here is the error I'm getting. Haven't been able to make sense of it
>> yet.
>>
>> *Sized> :load "JoinList.hs"
>> [1 of 2] Compiling Sized ( Sized.hs, interpreted )
>> [2 of 2] Compiling JoinList ( JoinList.hs, interpreted )
>>
>> JoinList.hs:50:21:
>> Could not deduce (b ~ Size)
>> from the context (Sized b, Monoid b)
>> bound by the type signature for
>> indexJ :: (Sized b, Monoid b) => Int -> JoinList b a ->
>> Maybe a
>> at JoinList.hs:44:11-63
>> `b' is a rigid type variable bound by
>> the type signature for
>> indexJ :: (Sized b, Monoid b) => Int -> JoinList b a -> Maybe
>> a
>> at JoinList.hs:44:11
>> Expected type: JoinList Size a
>> Actual type: JoinList b a
>> In the first argument of `tag', namely `x'
>> In the first argument of `getSize', namely `(tag x)'
>> In the first argument of `(>=)', namely `(getSize (tag x))'
>> Failed, modules loaded: Sized.
>>
>>
>>
>> thanks!
>>
>> --
>> Dustin Lee
>> qhfgva=rot13(dustin)
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
--
Dustin Lee
qhfgva=rot13(dustin)
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