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Today's Topics:
1. instance (Alexander Chen)
2. Re: instance (Ut Primum)
3. instance 2 (Alexander Chen)
4. Re: instance 2 (Ut Primum)
----------------------------------------------------------------------
Message: 1
Date: Wed, 22 Apr 2020 20:10:23 +0200 (CEST)
From: Alexander Chen <alexan...@chenjia.nl>
To: beginners@haskell.org
Subject: [Haskell-beginners] instance
Message-ID: <2038347538.89633.1587579022...@ichabod.co-bxl>
Content-Type: text/plain; charset="utf-8"
Hi,
data TisanInteger = Tisan Integer
instance Eq (Tisan Integer) where (Tisan v) == (Tisan v') = v == v'
prelude>
Instance_testen.hs:7:14: error:
Not in scope: type constructor or class ‘Tisan’
A data constructor of that name is in scope; did you mean DataKinds?
|
7 | instance Eq (Tisan Integer) where (Tisan v) == (Tisan v') = v == v' |
^^^^^
[1 of 1] Compiling Main ( Instance_testen.hs, interpreted )
Failed, no modules loaded.
what am i doing wrong?
best,
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Message: 2
Date: Wed, 22 Apr 2020 20:20:57 +0200
From: Ut Primum <utpri...@gmail.com>
To: Alexander Chen <alexan...@chenjia.nl>, The Haskell-Beginners
Mailing List - Discussion of primarily beginner-level topics related
to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] instance
Message-ID:
<canjdmklxyfn1guj3gjdkovmyu6c0ush8aahfpdhhzmuoc-d...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
data TisanInteger = Tisan Integer
instance Eq (*Tisan Integer*) where (Tisan v) == (Tisan v') = v == v'
I think the part in red is the error: you should write *TisanInteger*
instead (with no space between Tisan and Integer):
This is because there you should put the name of the data, not its
definition.
Best,
Ut
Il giorno mer 22 apr 2020 alle ore 20:11 Alexander Chen <
alexan...@chenjia.nl> ha scritto:
> Hi,
>
>
> *data TisanInteger = Tisan Integer*
>
> *instance Eq (Tisan Integer) where (Tisan v) == (Tisan v') = v == v'*
>
> *prelude>*
> *Instance_testen.hs:7:14: error:*
> * Not in scope: type constructor or class ‘Tisan’*
> * A data constructor of that name is in scope; did you mean DataKinds?*
> * |*
> *7 | instance Eq (Tisan Integer) where (Tisan v) == (Tisan v') = v == v'
> | ^^^^^*
> *[1 of 1] Compiling Main ( Instance_testen.hs, interpreted )*
> *Failed, no modules loaded.*
>
>
>
> what am i doing wrong?
>
> best,
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 3
Date: Wed, 22 Apr 2020 21:13:58 +0200 (CEST)
From: Alexander Chen <alexan...@chenjia.nl>
To: beginners@haskell.org
Subject: [Haskell-beginners] instance 2
Message-ID: <340361797.93178.1587582838...@ichabod.co-bxl>
Content-Type: text/plain; charset="utf-8"
hi,
data StringOrInt = TisanInt Int | TisAString String
instance Eq (StringOrInt) where
(==) (TisanInt v) (TisanInt v') = v == v'
(==) (TisAString s) (TisAString s') = s == s'
prelude>
Instance_testen.hs:4:37: error:
Ambiguous occurrence ‘==’
It could refer to either ‘Prelude.==’,
imported from ‘Prelude’ at Instance_testen.hs:1:1
(and originally defined in ‘GHC.Classes’)
or ‘Main.==’, defined at Instance_testen.hs:4:1
|
4 | (==) (TisanInt v) (TisanInt v') = v == v' |
^^
Instance_testen.hs:5:41: error:
Ambiguous occurrence ‘==’
It could refer to either ‘Prelude.==’,
imported from ‘Prelude’ at Instance_testen.hs:1:1
(and originally defined in ‘GHC.Classes’)
or ‘Main.==’, defined at Instance_testen.hs:4:1
|
5 | (==) (TisAString s) (TisAString s') = s == s'
| ^^
[1 of 1] Compiling Main ( Instance_testen.hs, interpreted )
Failed, no modules loaded.
what gives?
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Message: 4
Date: Wed, 22 Apr 2020 21:49:46 +0200
From: Ut Primum <utpri...@gmail.com>
To: Alexander Chen <alexan...@chenjia.nl>, The Haskell-Beginners
Mailing List - Discussion of primarily beginner-level topics related
to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] instance 2
Message-ID:
<canjdmklnylwb_rc0y0+qggvitudr-6hycopyppgp02jkf-c...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
I think the problem is indentation. Write the code this way:
data StringOrInt = TisanInt Integer | TisAString String
instance Eq (StringOrInt) where
(==) (TisanInt v) (TisanInt v') = v == v'
(==) (TisAString s) (TisAString s') = s==s'
where the red lines are indented (it means you have to leave two white
spaces at the beginning of those lines).
Ut
Il giorno mer 22 apr 2020 alle ore 21:14 Alexander Chen <
alexan...@chenjia.nl> ha scritto:
> hi,
>
> *data StringOrInt = TisanInt Int | TisAString String*
>
> *instance Eq (StringOrInt) where *
> *(==) (TisanInt v) (TisanInt v') = v == v'*
> *(==) (TisAString s) (TisAString s') = s == s'*
>
>
> *prelude>*
>
> *Instance_testen.hs:4:37: error:*
> * Ambiguous occurrence ‘==’*
> * It could refer to either ‘Prelude.==’,*
> * imported from ‘Prelude’ at
> Instance_testen.hs:1:1*
> * (and originally defined in ‘GHC.Classes’)*
> * or ‘Main.==’, defined at Instance_testen.hs:4:1*
> * |*
> *4 | (==) (TisanInt v) (TisanInt v') = v == v' |
> ^^*
>
> *Instance_testen.hs:5:41: error:*
> * Ambiguous occurrence ‘==’*
> * It could refer to either ‘Prelude.==’,*
> * imported from ‘Prelude’ at
> Instance_testen.hs:1:1*
> * (and originally defined in ‘GHC.Classes’)*
> * or ‘Main.==’, defined at Instance_testen.hs:4:1*
> * |*
> *5 | (==) (TisAString s) (TisAString s') = s == s' *
> * | ^^*
> *[1 of 1] Compiling Main ( Instance_testen.hs, interpreted )*
> *Failed, no modules loaded.*
>
>
>
> *what gives?*
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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