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Today's Topics:
1. Re: import not working (Galaxy Being)
2. Re: import not working (Travis Cardwell)
3. Better intro to the All About Monads tutorial? (Michael Turner)
----------------------------------------------------------------------
Message: 1
Date: Sat, 5 Jun 2021 17:23:32 -0500
From: Galaxy Being <borg...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] import not working
Message-ID:
<CAFAhFSUZ7ARhDWaqmy7Pa2o0LWe8rZ1QJFzen1oSwyy=iww...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Let me reiterate, I'm not creating a stack project formally. I'm just going
to some directory at the command prompt and firing up ghci, which I presume
just uses the global installs. Then I'm creating .hs files in a text editor
and trying to load them at the REPL. How can I install stuff in this
instance?
On Fri, Jun 4, 2021 at 10:47 PM Galaxy Being <borg...@gmail.com> wrote:
> I run ghci with
>
> > stack ghci
>
>
>
> On Fri, Jun 4, 2021 at 5:19 PM Jesse Rudel <jesse.ru...@gmail.com> wrote:
>
>> How are you invoking ghci? If it's a stack project you can try stack ghci
>> if you haven't already.
>>
>> On Fri, 4 Jun 2021 at 21:51, Galaxy Being <borg...@gmail.com> wrote:
>>
>>> I go to a directory. I run
>>>
>>> stack install Safe
>>>
>>> I start up ghci and get the Prelude prompt. I run
>>>
>>> import Safe
>>>
>>> and I get
>>>
>>> import Safe
>>> | ^^^^^^^^^^^
>>> Failed, no modules loaded.
>>>
>>> I'm once again frustrated. I try to load this hs file
>>>
>>> {-# LANGUAGE ViewPatterns #-}
>>> {-# LANGUAGE NoMonomorphismRestriction #-}
>>>
>>> import Safe
>>>
>>> lookupDefault :: Eq a => a -> b -> [(a,b)] -> b
>>> lookupDefault k _ (lookup k -> Just s) = s
>>> lookupDefault _ d _ = d
>>>
>>> headTup :: (a, [t]) -> [t]
>>> headTup (headMay . snd -> Just n) = [n]
>>> headTup _ = []
>>>
>>> headNil :: [a] -> [a]
>>> headNil (headMay -> Just x) = [x]
>>> headNil _ = []
>>>
>>> with the same result. What do I need to do?
>>> --
>>> ⨽
>>> Lawrence Bottorff
>>> Grand Marais, MN, USA
>>> borg...@gmail.com
>>> _______________________________________________
>>> Beginners mailing list
>>> Beginners@haskell.org
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>
>
> --
> ⨽
> Lawrence Bottorff
> Grand Marais, MN, USA
> borg...@gmail.com
>
--
⨽
Lawrence Bottorff
Grand Marais, MN, USA
borg...@gmail.com
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Message: 2
Date: Sun, 6 Jun 2021 09:32:25 +0900
From: Travis Cardwell <travis.cardw...@extrema.is>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] import not working
Message-ID:
<CACaJP_T3=7+uhu1oejuifl2revgtdx5vtoj3mnhejqeuqfd...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
The `stack ghci` command does not load extra packages such as those
installed "globally." This is a good thing, IMHO. You can instruct
the command to load specific packages using the `--package` option.
Example:
stack repl --package safe
Example using your file:
stack repl --package safe GalaxyBeing.hs
Note that your email indicates usage of the `Safe` package (uppercase),
but that package is deprecated in favor of the `safe` package
(lowercase). I mention it in case it is not intentional.
* <https://hackage.haskell.org/package/safe>
* <https://hackage.haskell.org/package/Safe>
You may want to create a project that is just for testing. You can then
specify which Stack snapshot to use in `stack.yaml` and which packages
to use in `package.yaml`.
stack new experiment
Travis
------------------------------
Message: 3
Date: Sun, 6 Jun 2021 10:50:08 +0900
From: Michael Turner <michael.eugene.tur...@gmail.com>
To: beginners@haskell.org
Subject: [Haskell-beginners] Better intro to the All About Monads
tutorial?
Message-ID:
<CANHeBihjJLL_t=-8vj2e9dZQT5T7Pr=ozgew_q9okq8p7bc...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
I've done some work on this page:
https://wiki.haskell.org/All_About_Monads
I could use some help in improving my improvements
1. Beginners -- if you haven't looked at monads yet, does this new
intro boost your confidence?
2. Those who help beginners here -- have I committed any technical errors?
I was a little frustrated about the text as it stood. For example:
"... a monad is a way to structure computations in terms of values and
sequences of computations using typed values. Monads allow the
programmer to build up computations using sequential building blocks,
which can themselves be sequences of computations. The monad
determines how combined computations form a new computation and frees
the programmer from having to code the combination manually each time
it is required."
The problem with this was that you could substitute "compiler" or "C++
class" and it would be not much less true and not much more
uninformative. The approach I took to rewriting (aside from where I
take the reader's hand gently at the beginning) was to try to anchor
the treatment more in concepts that the reader might already
understand. The two main concepts were were pipelines (as in shell
programming) and "cross-cutting concerns" (with links to Wikipedia
articles for readers who might not know one or the other or both.)
I've left almost all of the original wording intact and just wrote
around it. Perhaps it could be trimmed, maybe even a lot.
I don't understand monads well enough to write one myself yet. But I
think a newbie perspective can help in writing for newbies: unlike the
expert, the sources of confusion and incomprehension are fresh in your
mind, as are the ways you got past them.
Regards,
Michael Turner
Executive Director
Project Persephone
1-25-33 Takadanobaba
Shinjuku-ku Tokyo 169-0075
Mobile: +81 (90) 5203-8682
tur...@projectpersephone.org
Understand - http://www.projectpersephone.org/
Join - http://www.facebook.com/groups/ProjectPersephone/
Donate - http://www.patreon.com/ProjectPersephone
Volunteer - https://github.com/ProjectPersephone
"Love does not consist in gazing at each other, but in looking outward
together in the same direction." -- Antoine de Saint-Exupéry
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