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Today's Topics:
1. Stack could not find libHStransformers (Quentin Liu)
2. Re: Stack could not find libHStransformers (Michael Snoyman)
3. Little question about "forall" (Baa)
----------------------------------------------------------------------
Message: 1
Date: Thu, 7 Dec 2017 01:43:22 -0500
From: Quentin Liu <quentin.liu.0...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: [Haskell-beginners] Stack could not find libHStransformers
Message-ID: <d377cf51-f745-441e-a6e8-8493e47ab013@Spark>
Content-Type: text/plain; charset="utf-8"
Hi,
I was trying to use Parsec and imported Text.ParserCombinators.Parsec. I could
call “stack ghc” to compile the file, but when I loaded the file into ghci and
called any function, ghci would report errors
> can't load .so/.DLL for:
> /Users/HereWegoR/.stack/snapshots/x86_64-osx/lts-8.8/8.0.2/lib/x86_64-osx-ghc-8.0.2/libHSmtl-2.2.1-BLKBelFsPB3BoFeSWSOYj6-ghc8.0.2.dylib
>
> (dlopen(/Users/HereWegoR/.stack/snapshots/x86_64-osx/lts-8.8/8.0.2/lib/x86_64-osx-ghc-8.0.2/libHSmtl-2.2.1-BLKBelFsPB3BoFeSWSOYj6-ghc8.0.2.dylib,
> 5): Library not loaded:
> /usr/local/opt/ghc/lib/ghc-8.0.2/transformers-0.5.2.0/libHStransformers-0.5.2.0-ghc8.0.2.dylib
> Referenced from:
> /Users/HereWegoR/.stack/snapshots/x86_64-osx/lts-8.8/8.0.2/lib/x86_64-osx-ghc-8.0.2/libHSmtl-2.2.1-BLKBelFsPB3BoFeSWSOYj6-ghc8.0.2.dylib
> Reason: image not found)
>
I tried to install transformers by calling `stack install transformers` but the
problem still persisted. Is it because the version of transformers in my repo
is different from the one referenced by `mtl` package? How should I fix it?
Regards,
Qingbo Liu
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Message: 2
Date: Thu, 7 Dec 2017 08:54:45 +0200
From: Michael Snoyman <mich...@snoyman.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Stack could not find
libHStransformers
Message-ID:
<CAKT9ecPjwAJjEZEE3ZWvQ4TBoVrN6PeXW5LbHHbuLEnX8=k...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
What version of Stack are you using (stack --version), and how did you
install Stack and GHC?
It looks like you're using a system-wide GHC installation, which (for
reasons like this) we by default no longer use by default in recent Stack
releases.
Upgrading to the latest Stack (via `stack upgrade` or following the
instructions at [1]) will probably solve the problem.
[1] https://haskell-lang.org/get-started/osx
On Thu, Dec 7, 2017 at 8:43 AM, Quentin Liu <quentin.liu.0...@gmail.com>
wrote:
> Hi,
>
> I was trying to use Parsec and imported Text.ParserCombinators.Parsec. I
> could call “stack ghc” to compile the file, but when I loaded the file into
> ghci and called any function, ghci would report errors
>
> can't load .so/.DLL for: /Users/HereWegoR/.stack/
> snapshots/x86_64-osx/lts-8.8/8.0.2/lib/x86_64-osx-ghc-8.0.
> 2/libHSmtl-2.2.1-BLKBelFsPB3BoFeSWSOYj6-ghc8.0.2.dylib
> (dlopen(/Users/HereWegoR/.stack/snapshots/x86_64-osx/
> lts-8.8/8.0.2/lib/x86_64-osx-ghc-8.0.2/libHSmtl-2.2.1-
> BLKBelFsPB3BoFeSWSOYj6-ghc8.0.2.dylib, 5): Library not loaded:
> /usr/local/opt/ghc/lib/ghc-8.0.2/transformers-0.5.2.0/
> libHStransformers-0.5.2.0-ghc8.0.2.dylib
> Referenced from: /Users/HereWegoR/.stack/snapshots/x86_64-osx/lts-8.8/
> 8.0.2/lib/x86_64-osx-ghc-8.0.2/libHSmtl-2.2.1-
> BLKBelFsPB3BoFeSWSOYj6-ghc8.0.2.dylib
> Reason: image not found)
>
>
> I tried to install transformers by calling `stack install transformers`
> but the problem still persisted. Is it because the version of transformers
> in my repo is different from the one referenced by `mtl` package? How
> should I fix it?
>
> Regards,
> Qingbo Liu
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
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Message: 3
Date: Thu, 7 Dec 2017 13:41:08 +0200
From: Baa <aqua...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: [Haskell-beginners] Little question about "forall"
Message-ID: <20171207134108.1ae548b8@Pavel>
Content-Type: text/plain; charset=US-ASCII
Hello everyone!
Suppose I have:
class C a where
someA :: a
f :: C a => a -> Int
f a =
let x = someA :: a in -- BUG!!
0
BUG as I understand I due to `:: a` - this is another `a`, not the same as
in `f` singature. But seems that it's the same `a` if `f` is the "method"
of some instance. And such bug does not happen if I return it, so my question
is how to create such `x` of type `a` in the body of the `f`? How to use
`a` anywhere in the body of `f`? Is it possible?
I found a way if I change signature to `forall a. C a => a -> Int`. But there
are another questions in the case:
- as I know all such params are under "forall" in Haskell by-default. Seems
it's not true?
- in method body seems they are under "forall" but in simple functions - not?
- i'm not sure what exactly does this "forall", IMHO it unbounds early bound
type's variables (parameters) by typechecker, but how `a` can be bound in the
just begining of signature (where it occurs first time) ?!
As for me, looks that w/o "forall" all `a`, `b`, `c`, etc in the body of
simple functions always are different types. But w/ "forall" Haskell typechecker
makes something like (on type-level):
let a = ANY-TYPE
in
... here `a` can occur and will be bound to ANY-TYPE
Where am I right and where am I wrong? :)
===
Best regards, Paul
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