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Today's Topics:
1. Lifting over record syntax (Jaakko Luttinen)
2. Re: I can't start WinGHCi Haskell (Ut Primum)
----------------------------------------------------------------------
Message: 1
Date: Sun, 14 Oct 2018 10:15:06 +0300
From: Jaakko Luttinen <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Lifting over record syntax
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi!
Let's consider this simple data structure:
data Person = Person {name::String, age::Int} deriving Show
Now, I can create maybe-people like in applicative style:
Person <$> Just "John Doe" <*> Nothing
or in monad style:
do
name' <- Just "John Doe"
age' <- Nothing
return Person {name=name', age=age'}
The problem with the first approach is that it depends on the order of
the arguments because it doesn't utilize the record syntax. The problem
with the second approach is that there's a bit of unnecessary
boilerplate (e.g., name' and age' variables).
I would like to get the benefits of the the record syntax but with
similar code simplicity as the applicative style has. Do you have ideas
is this possible? My non-working pseudo-code would look like:
Person <$> {name=Just "John Doe", age=Nothing}
But this doesn't work, it's syntax error.
Any ideas for a nice syntax?
Cheers,
Jaakko
------------------------------
Message: 2
Date: Sun, 14 Oct 2018 09:49:38 +0200
From: Ut Primum <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] I can't start WinGHCi Haskell
Message-ID:
<CANjDmKJp=dprqhefvhwxmquqkx-+-jhw0tv9grwddscwcw4...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Sometimes this kind of errors are caused by the fact that the PATH
environment variable hasn't been modified correctly during installation, so
maybe you should do it manually
Il dom 14 ott 2018, 02:58 Brody Berg <[email protected]> ha scritto:
> Looks like it isn’t installed correctly - or something it depends on is
> missing.
>
> On Sat, Oct 13, 2018 at 17:45 Gustavo Arturo Marquez Flores <
> [email protected]> wrote:
>
>> Hi,
>>
>> I want to start with Haskell language programming. But when I launch
>> the WinGHCi program I got he followin message:
>>
>> [image: image.png]
>>
>> What can I do ? How to resolve this problem ? I use Windows 10 plataform.
>>
>> I aprecite your help for resolving this problem to me.
>>
>> Thanks a lot.
>> _______________________________________________
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