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Today's Topics:
1. Re: How to use Text.Printf w/ custom types (Baa)
2. Re: How to use Text.Printf w/ custom types (Norbert Melzer)
3. Re: How to use Text.Printf w/ custom types (Baa)
4. Re: Why do i need to specify the class of a here at all?
(Quentin Liu)
----------------------------------------------------------------------
Message: 1
Date: Fri, 24 Nov 2017 16:07:19 +0200
From: Baa <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] How to use Text.Printf w/ custom
types
Message-ID: <20171124160719.7292469f@Pavel>
Content-Type: text/plain; charset=US-ASCII
I talked about PrintfType and its method `hspr`.
With PrintfArgs the same problem:
instance PrintfArg JobEvent where
toUPrintf _ = UString "aaa"
^^^ toUPrintf is not visible ERROR here...
Header of this file looks like:
module Text.Printf(
printf, hPrintf,
PrintfType, HPrintfType, PrintfArg, IsChar
) where
so methods are not exported? And I don't see any Internal subpackage...
OK, no problem, I switched already to very cool `formatting` library :)
Thanks a lot!
> It appears PrintfArg and its methods are fully exported.
>
> On Fri, Nov 24, 2017 at 8:19 AM, Baa <[email protected]> wrote:
>
> > But how to do it if "methods" are not exporting?
> >
> > > According to
> > > https://hackage.haskell.org/package/base-4.10.0.0/docs/
> > Text-Printf.html#g:2,
> > > you only need to implement `PrintfArg`. There is also an example
> > > for `()`.
> > >
> > > Baa <[email protected]> schrieb am Fr., 24. Nov. 2017 um 13:33
> > > Uhr:
> > > > Hello All!
> > > >
> > > > As I understand to use Text.Printf.printf with custom types or
> > > > to return result as Text instead of String I must implement some
> > > > class instances: PrintfType, PrintfArg. But how to do this if
> > > > they are exported from module as type-names only - without its
> > > > methods (i.e. not "Printf (..)", but "Printf") ?
> > > >
> > > > I tried to import Text.Printf.Internal but seems that no such
> > > > submodule...
> > > >
> > > > Any ideas?
> > > >
> > > > ===
> > > > Best regards, Paul
> > > > _______________________________________________
> > > > Beginners mailing list
> > > > [email protected]
> > > > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> > > >
> >
> > _______________________________________________
> > Beginners mailing list
> > [email protected]
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >
------------------------------
Message: 2
Date: Fri, 24 Nov 2017 15:36:25 +0000
From: Norbert Melzer <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] How to use Text.Printf w/ custom
types
Message-ID:
<ca+bcvsutkmspfr9uvqwjazsez4wuwen3bapb-2ddkdf2bz+...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
PrintfArg does not have toUPrint. The functions in there are formatArg and
parseFormat.
PrintfType is according to its documentation, an interface that you shall
not implement yourself.
Baa <[email protected]> schrieb am Fr., 24. Nov. 2017 um 15:08 Uhr:
> I talked about PrintfType and its method `hspr`.
>
> With PrintfArgs the same problem:
>
> instance PrintfArg JobEvent where
> toUPrintf _ = UString "aaa"
>
> ^^^ toUPrintf is not visible ERROR here...
>
> Header of this file looks like:
>
> module Text.Printf(
> printf, hPrintf,
> PrintfType, HPrintfType, PrintfArg, IsChar
> ) where
>
> so methods are not exported? And I don't see any Internal subpackage...
> OK, no problem, I switched already to very cool `formatting` library :)
>
> Thanks a lot!
>
>
> > It appears PrintfArg and its methods are fully exported.
> >
> > On Fri, Nov 24, 2017 at 8:19 AM, Baa <[email protected]> wrote:
> >
> > > But how to do it if "methods" are not exporting?
> > >
> > > > According to
> > > > https://hackage.haskell.org/package/base-4.10.0.0/docs/
> > > Text-Printf.html#g:2,
> > > > you only need to implement `PrintfArg`. There is also an example
> > > > for `()`.
> > > >
> > > > Baa <[email protected]> schrieb am Fr., 24. Nov. 2017 um 13:33
> > > > Uhr:
> > > > > Hello All!
> > > > >
> > > > > As I understand to use Text.Printf.printf with custom types or
> > > > > to return result as Text instead of String I must implement some
> > > > > class instances: PrintfType, PrintfArg. But how to do this if
> > > > > they are exported from module as type-names only - without its
> > > > > methods (i.e. not "Printf (..)", but "Printf") ?
> > > > >
> > > > > I tried to import Text.Printf.Internal but seems that no such
> > > > > submodule...
> > > > >
> > > > > Any ideas?
> > > > >
> > > > > ===
> > > > > Best regards, Paul
> > > > > _______________________________________________
> > > > > Beginners mailing list
> > > > > [email protected]
> > > > > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> > > > >
> > >
> > > _______________________________________________
> > > Beginners mailing list
> > > [email protected]
> > > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> > >
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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------------------------------
Message: 3
Date: Fri, 24 Nov 2017 18:23:55 +0200
From: Baa <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] How to use Text.Printf w/ custom
types
Message-ID: <20171124182355.7a8b0726@Pavel>
Content-Type: text/plain; charset=US-ASCII
Oh, seems that it's my error! You are right.
> PrintfArg does not have toUPrint. The functions in there are
> formatArg and parseFormat.
>
> PrintfType is according to its documentation, an interface that you
> shall not implement yourself.
>
> Baa <[email protected]> schrieb am Fr., 24. Nov. 2017 um 15:08 Uhr:
>
> > I talked about PrintfType and its method `hspr`.
> >
> > With PrintfArgs the same problem:
> >
> > instance PrintfArg JobEvent where
> > toUPrintf _ = UString "aaa"
> >
> > ^^^ toUPrintf is not visible ERROR here...
> >
> > Header of this file looks like:
> >
> > module Text.Printf(
> > printf, hPrintf,
> > PrintfType, HPrintfType, PrintfArg, IsChar
> > ) where
> >
> > so methods are not exported? And I don't see any Internal
> > subpackage... OK, no problem, I switched already to very cool
> > `formatting` library :)
> >
> > Thanks a lot!
> >
> >
> > > It appears PrintfArg and its methods are fully exported.
> > >
> > > On Fri, Nov 24, 2017 at 8:19 AM, Baa <[email protected]> wrote:
> > >
> > > > But how to do it if "methods" are not exporting?
> > > >
> > > > > According to
> > > > > https://hackage.haskell.org/package/base-4.10.0.0/docs/
> > > > Text-Printf.html#g:2,
> > > > > you only need to implement `PrintfArg`. There is also an
> > > > > example for `()`.
> > > > >
> > > > > Baa <[email protected]> schrieb am Fr., 24. Nov. 2017 um 13:33
> > > > > Uhr:
> > > > > > Hello All!
> > > > > >
> > > > > > As I understand to use Text.Printf.printf with custom types
> > > > > > or to return result as Text instead of String I must
> > > > > > implement some class instances: PrintfType, PrintfArg. But
> > > > > > how to do this if they are exported from module as
> > > > > > type-names only - without its methods (i.e. not "Printf
> > > > > > (..)", but "Printf") ?
> > > > > >
> > > > > > I tried to import Text.Printf.Internal but seems that no
> > > > > > such submodule...
> > > > > >
> > > > > > Any ideas?
> > > > > >
> > > > > > ===
> > > > > > Best regards, Paul
> > > > > > _______________________________________________
> > > > > > Beginners mailing list
> > > > > > [email protected]
> > > > > > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> > > > > >
> > > >
> > > > _______________________________________________
> > > > Beginners mailing list
> > > > [email protected]
> > > > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> > > >
> >
> > _______________________________________________
> > Beginners mailing list
> > [email protected]
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >
------------------------------
Message: 4
Date: Fri, 24 Nov 2017 14:04:39 -0500
From: Quentin Liu <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Why do i need to specify the class of
a here at all?
Message-ID: <5fdec6dc-aeb8-4083-9782-114c0c1c8b6c@Spark>
Content-Type: text/plain; charset="utf-8"
> > > Yes, you could pass the function a list of strings as well. A string is
> > > just a list of Chars. The type signature `a` does not restrict the range
> > > of types you could pass to the function.
> >
> > That seem strange to me. Wouldn't that mean that i could write the
> > declaration of myOrderFunc as `myOrderFunc :: a -> a -> Ordering` as well?
> > GHCI give me an error on this though so obviously it's wrong. I just don't
> > see why. Why cannot a represent [b]?
Could you copy and paste the error message here?
The type signature `a` means it could be anything, `String`, `[String]`, or any
ADT you could come up with. So in a type signature if you write
func :: a -> a -> a
func a b = a
this funciton is telling ghc that I have a function that accepts two parameters
that must be of the same type, whatever the type is. So `a` could be an ADT, a
list, a list of lists, etc. But if you write
func :: a -> [b] -> a
func a bs = a
you are essentially saying this function would only take two parameters of two
types (`a` and `b` could be of the same type) and the second parameter must be
a list. This, however, does not suggest mean that `[b]` could not be
`[[String]]`, for `[String]` could just be thought of as a `b`. The way I use
to think about type signature is, when you trying to substitute type variables
such as `a`, substitute it into a concrete type that you are working with.
Regards,
Qingbo Liu
On Nov 23, 2017, 03:19 -0500, mrx <[email protected]>, wrote:
> > On Wed, Nov 22, 2017 at 10:40 PM, Quentin Liu <[email protected]>
> > wrote:
> > > Hi Patrik,
> > >
> > > The reason for the requirement of “Eq a” in your `sortListOfLists` is
> > > that you are calling myOrderFunc which carries the signature “Eq a”. If
> > > you remove the `Eq` declaration in `myOrderFunc` the compiler then would
> > > not complain about the absence of `Eq` in `sortListOfLists`. For a
> > > detailed explanation you could reference chapter 6 of Real World Haskell.
> >
> > Thanks a lot for the reference. I'll make sure to read that chapter soon.
> >
> > >
> > > Yes, you could pass the function a list of strings as well. A string is
> > > just a list of Chars. The type signature `a` does not restrict the range
> > > of types you could pass to the function.
> >
> > That seem strange to me. Wouldn't that mean that i could write the
> > declaration of myOrderFunc as `myOrderFunc :: a -> a -> Ordering` as well?
> > GHCI give me an error on this though so obviously it's wrong. I just don't
> > see why. Why cannot a represent [b]?
> >
> // Patrik
> _______________________________________________
> Beginners mailing list
> [email protected]
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