Haskell Channel Logs: #haskell channel featuring recur22, Athas, shapr, cocreature, glguy, kadoban, and 38 others.

fendoer 2017-02-27 01:45:27

https://hastebin.com/exanucasez.sql

fendor 2017-02-27 01:45:53

posted it from another device

cocreature 2017-02-27 01:46:14

alright, that does look like a cabal problem. are you sure that you have cleaned up ~/.ghc?

cocreature 2017-02-27 01:46:34

if so, what ghc & cabal version are you using?

fendor 2017-02-27 01:48:05

GHC: 8.0.1

fendor 2017-02-27 01:48:13

cabal-install 1.24

dcoutts 2017-02-27 01:48:21

fendoer: are you quite sure you removed ~/.ghc ?

fendor 2017-02-27 01:48:34

yes, i am, but i can redo it, to be sure

dcoutts 2017-02-27 01:48:48

after that, does ghc-pkg list show any packages marked as broken?

oisdk 2017-02-27 01:49:10

lyxia Looks like this might work. Thanks!

fendor 2017-02-27 01:49:38

well, ghc is marked blue, the rest is white, and no packages claims to be broken

dcoutts 2017-02-27 01:49:48

that's ok then

dcoutts 2017-02-27 01:50:47

fendor: and just to check, that list does not include 'text' right?

fendor 2017-02-27 01:51:16

it does, text-1.2.2.1

fendor 2017-02-27 01:51:33

this might be from the package manager of solus

cocreature 2017-02-27 01:51:45

fendor: what directory does ghc-pkg list for text?

dcoutts 2017-02-27 01:51:50

ok, well that's the one your build log is complaining about

mohsen_ 2017-02-27 01:51:54

-/quit

fendor 2017-02-27 01:52:12

ok, so, maybe cabal is biting itself because of the OS package manager?

dcoutts 2017-02-27 01:52:31

fendor: certainly it will try to use the one your OS package manger installed

dcoutts 2017-02-27 01:52:40

and if that one is busted then...

suppi 2017-02-27 01:53:23

can i suggest downloading a stack binary instead?

fendor 2017-02-27 01:54:58

well, if it worked out correctly, the would be incredible easy to install packages and not having any struggles with cabal

cocreature 2017-02-27 01:55:24

dcoutts: yes please!

fendor 2017-02-27 01:55:32

a stack binary would probably do fine, but it just bugs me, that it does not work

suppi 2017-02-27 01:55:40

fendor: why not download a stack binary? why install via cabal?

suppi 2017-02-27 01:55:48

dcoutts 2017-02-27 01:56:18

stack will have the same problem if you have stack using your system ghc of course

suppi 2017-02-27 01:56:33

then don't :)

fendor 2017-02-27 01:56:56

so, solution: dont use the package manager?

dcoutts 2017-02-27 01:57:22

there are often good reasons to use the system package manager

suppi 2017-02-27 01:57:25

the os one for installing stack?

cocreature 2017-02-27 01:57:37

fendor: what exactly have you installed via your package manager? maybe it provides a package that contains just ghc and not additional packages like "text"

suppi 2017-02-27 01:57:59

it's probably not a problem. i uses the os one to install stack

fendor 2017-02-27 01:58:42

the os does not provide a package for stack, i submitted the suggestion to do so, but currently i cant install it via the package manager

fendor 2017-02-27 01:59:18

cocreature: i actively installed packages like text via the package manager, so it seems to be the problem

suppi 2017-02-27 01:59:20

so yeah, don't use it if you can't...

cocreature 2017-02-27 01:59:33

fendor: in that case, just uninstall them :)

cocreature 2017-02-27 01:59:53

installing ghc via the package manager is fine, installing other haskell packages via the package manager is usually not worth the trouble

fendor 2017-02-27 02:04:46

yeah, i see

fendor 2017-02-27 02:06:52

doing that right now

fendor 2017-02-27 02:08:14

*sigh* why does this not work?

cocreature 2017-02-27 02:08:14

uninstalling does('t work?

fendor 2017-02-27 02:08:14

no, packages via the package manager? i removed everything except for the cabal package of Solus, and it is building right now, seems to work, but dont know yet

cocreature 2017-02-27 02:08:14

the problem is that you can easily get into a situation where you need a different version of a package than the one provided by your package manager. however if a package is installed into the global package database (as done by the package manager) that package is always available so you can't just install a different version since they would conflict. In your particular case the packages provided by

cocreature 2017-02-27 02:08:14

your package manager also seem to be broken which might be the fault of the distribution

suppi 2017-02-27 02:08:14

no one writing a library wants to write and maintain a package for every package manager out there

fendor 2017-02-27 02:08:31

so it is indeed a bad idea to use a package manager for the packages used by a language, in this case haskell?

hpc 2017-02-27 02:08:44

sometimes

suppi 2017-02-27 02:08:51

imo, definitely

hpc 2017-02-27 02:09:00

if you know ahead of time that you are never going to need anything the OS doesn't provide, it's safe to use just packages

hpc 2017-02-27 02:09:10

mixing is what causes trouble

hpc 2017-02-27 02:09:28

so for instance, if you didn't intend to do any haskell development at all and just wanted pandoc

fendor 2017-02-27 02:09:34

so, either the packages manager needs to be more exhaustive or dont use it at all? what a pity...

Clint 2017-02-27 02:09:35

fendor: i use packages exclusively

hpc 2017-02-27 02:09:38

that's fine to get from the package manager instead of building it yourself with cabal

hpc 2017-02-27 02:09:56

but you get a sudden urge to write some code and now you need to cabal install lens or something

cocreature 2017-02-27 02:09:56

fendor: I usually tend to use the packages provided by the package manager if I want to use a package written in a language but not hack on one myself. in the latter case I ignore the system package manager

hpc 2017-02-27 02:10:31

and now you're screwed, because cabal isn't able to control how the pre-packaged packages are built

fendor 2017-02-27 02:11:01

so in short if i want to develop with haskell, i cant use the os package manager?

hpc 2017-02-27 02:11:06

stack solves the problem by working around it entirely, and managing its own everything

fendor 2017-02-27 02:11:11

just if i want to execute some code?

suppi 2017-02-27 02:11:21

just use stack with haskell

dcoutts 2017-02-27 02:11:27

fendor: I think typical practice is to install ghc via system package manager, but nothing else

hpc 2017-02-27 02:11:37

fendor: you can, but it leads to trouble when you try to do certain things

hpc 2017-02-27 02:11:40

and it's not worth the trouble

dcoutts 2017-02-27 02:12:20

fendor: because then by using cabal or stack you can control exactly what versions of haskell packages are used for everything else, including choosing different versions for different projects

fendor 2017-02-27 02:17:11

well, stack seems to work for now, thx guys, i'm a little disappointed in the package manager now, but whatever, thanks guys!

recur22 2017-02-27 02:19:41

hpc: no ffi, i'm looking for translation from code to code

Tuplanolla 2017-02-27 02:49:55

Symbolic algebra without the woes of an imperative language, recur22.

cocreature 2017-02-27 02:53:10

recur22: is there any specific C library you have in mind?

Athas 2017-02-27 02:53:21

glibc!

recur22 2017-02-27 02:53:29

yes

juri_ 2017-02-27 02:53:36

libc5. :)

juri_ 2017-02-27 02:54:41

parts of VLC would be neat to see.

recur22 2017-02-27 02:55:20

is it big yes, will you be intersted in i doubt it

kubunto 2017-02-27 03:40:12

are eithers biased in haskell

locallycompact 2017-02-27 03:40:50

what does that mean?

kubunto 2017-02-27 03:41:02

locallycompact: left is wrong, right is right

kubunto 2017-02-27 03:41:28

or left is fail, right is success

locallycompact 2017-02-27 03:43:01

Either a b is just a type, but the default Functor implementation chains via the right hand type, if that's what you mean

bpa2 2017-02-27 03:43:15

Thank you Hafyddh SetBuffering stdout NoBuffering did the trick.

mniip 2017-02-27 03:43:20

performance wise they are unbiased

locallycompact 2017-02-27 03:43:46

so you can have a functor instance for Either String a

mniip 2017-02-27 03:45:18

locallycompact, nit: without the a

kubunto 2017-02-27 03:45:38

locallycompact: functor?

dram_phone 2017-02-27 04:55:51

Guest86134: On a second thought, that doesn't seem right to me

dram_phone 2017-02-27 04:56:24

if you have h(A) and unify A with h(B) how are you going to prevent h(h(B))...

dram_phone 2017-02-27 04:56:40

I think I should stop messing up your thoughts. Sorry

drostie 2017-02-27 04:58:17

kubunto: then in JS you can write `function zipWith(fn, a, b) { return {first: fn(a.first, b.first), rest: () => zipWith(fn, a.rest(), b.rest())} }` and then finally you can write `var fibs = {first: 0, rest: () => {first: 1, rest: () => zipWith((x, y) => x + y, fibs, fibs.rest())}}` and it will make sense.

kubunto 2017-02-27 04:58:20

drostie: i am workign thru learn you a haskell tutorial

Guest86134 2017-02-27 05:00:27

dram_phone: np, thanks for the help so far! :) (I will never want to unify A with h(B), only flat structures)

drostie 2017-02-27 05:00:50

kubunto: LYAH is ok if you have a very playful mind, but not necessarily the best if you want to get quickly up to speed with hard pragmatics.

dram_phone 2017-02-27 05:00:50

hmm, then why are you even doing that difficult unification business

drostie 2017-02-27 05:00:50

kubunto: I wanted to say that the second way that Haskell is Different is that we have a data type for programs which interact with the world. In most other languages interacting with the world is done with side-effects.

dram_phone 2017-02-27 05:00:50

Just get a union-find sets of variables

drostie 2017-02-27 05:00:50

kubunto: so you call `Math.random()` in JavaScript and as a side-effect it stores some new seed in memory so that future calls to `Math.random()` generate different results.

drostie 2017-02-27 05:01:24

kubunto: In Haskell things like `Date.now()` and `Math.random()` and `console.log()` are instead going to be values of the program type. So they won't do anything by default. Instead the goal of your Haskell program is to create a program which returns `()` called `main`, and this will be spat out as an executable for you to run later.

drostie 2017-02-27 05:02:11

kubunto: in that respect your approach of starting with GHCi is going to confuse you a little bit.

kubunto 2017-02-27 05:02:12

what dram_phone said

dram_phone 2017-02-27 05:02:22

And speaking of Python, TBH when I choose Python over Haskell it's almost always because ready-made bindings

dram_phone 2017-02-27 05:02:58

are better than ad-hoc bindings by me...

drostie 2017-02-27 05:03:02

Because GHCi has the semantics of "if you type in a program, I'm going to run the program and print whatever it produces; if you type in a value I'm going to print the value" and you don't necessarily get this language-crucial feedback of "oh, crap, that was a program."

dram_phone 2017-02-27 05:03:24

That's a good point there

drostie 2017-02-27 05:03:42

kubunto: ok, ymmv. It's just that those two things were the important ones I wish someone had told me when I was starting Haskell by playing around with GHCi.

drostie 2017-02-27 05:04:13

kubunto: helps to, right before you run anything with GHCI, first ask GHCI what its type is.

kubunto 2017-02-27 05:04:23

drostie 2017-02-27 05:04:27

yep.

Cale 2017-02-27 05:05:32

It's worth noting that these things (IO actions) that drostie is referring to as "programs" are themselves also values.

drostie 2017-02-27 05:05:37

then it will tell you, in response to `:t getLine >>= putStrLn` that this is of type `getLine >>= putStrLn :: IO ()`, it is a program which produces a `()` [the unit type, you can think of it as a "null" if you want.]

Cale 2017-02-27 05:06:04

GHCi just has a bunch of special cases for what to do based on the type of the expression you enter.

Tuplanolla 2017-02-27 05:08:51

Are there any remedies to making multithreaded resource management less hard? I keep finding problems where threads die while holding `MVar`s or cause races when passing messages.

Cale 2017-02-27 05:11:02

Well, with respect to the races, STM can help somewhat

Cale 2017-02-27 05:11:05

(by letting you build up transactions which either happen as if they occurred all at once, or not at all)

Cale 2017-02-27 05:11:06

Use withMVar rather than takeMVar and putMVar whenever possible

Cale 2017-02-27 05:11:06

It handles exceptions better.

Tuplanolla 2017-02-27 05:11:07

Sockets and temporary files are my main gripe today.

geekosaur 2017-02-27 05:20:58

but are they raw on disk, or is there a header or etc.?

Cale 2017-02-27 05:21:47

Yeah, I'm assuming that the bytestring was written directly, and yes, it will skip forward to the position you specify without needing to read in the whole file up to that point

danilo2 2017-02-27 05:22:37

geekosaur: in fact they dont exist yet. I want to be able to store some big bytestring on disk and have access to some bytes form given range

danilo2 2017-02-27 05:22:48

geekosaur, Cale: cool , thank you for your help! :)

Guest82102 2017-02-27 05:22:48

does anyone in here use spacemacs?

bennofs 2017-02-27 05:22:49

yes

geekosaur 2017-02-27 05:22:49

right, in tht case iyt' just a seek. although it may still read the file up to that point if it's small enough to not be worth it... but that's largely for the OS to decide

Guest82102 2017-02-27 05:23:56

bennofs, with stack?

kubunto 2017-02-27 05:25:53

ill be back if i has more questions

bennofs 2017-02-27 05:25:53

Guest82102: yes

kadoban 2017-02-27 05:25:53

Anyone know offhand if there's anything particularly clever done by readInteger for converting large integers from ByteString? Apparently this wasn't supposed to be possible with bigints https://www.hackerrank.com/contests/w29/challenges/big-sorting , and I've been told that in other languages it fails spectacularly, but it just works in haskell

Guest82102 2017-02-27 05:26:11

bennofs, do you know how i can pass ghci-options to the intero repl? somewhere in .spacemacs?

bennofs 2017-02-27 05:26:27

Guest82102: uh, no idea, sorry

cocreature 2017-02-27 05:27:03

kadoban: if you can only parse small integers and then have to convert them to a big integer it might get a bit more complicated

glguy 2017-02-27 05:38:37

It's possible that the rpi doesn't have enough ram to compile a new cabal-install starting with GHC 8.0.2

Rub_ixCube 2017-02-27 05:38:48

1GB is enough

glguy 2017-02-27 05:38:56

I was able to do it with 8.0.1 and I seem to remember OOM on 8.0.2

glguy 2017-02-27 05:39:11

Why do you believe that 1GB is enough?

Rub_ixCube 2017-02-27 05:39:19

Chrome runs well :)

glguy 2017-02-27 05:39:26

That's not how numbers work

kadoban 2017-02-27 05:39:42

Heh

bennofs 2017-02-27 05:39:48

Haskell blows your expectations. Regarding memory usage

Cale 2017-02-27 05:39:48

I have 16GB in my laptop and it's barely enough for my work setup

bennofs 2017-02-27 05:40:11

(I should say "GHC")

Rub_ixCube 2017-02-27 05:40:12

Rub_ixCube 2017-02-27 05:40:17

oh ye

kadoban 2017-02-27 05:40:28

Yeah, GHC/haskell is unfortunately quite memory heavy. I used to run into trouble on my old machine with 2GB, and even on my current one with 4GB I sometimes wish I had more.

Cale 2017-02-27 05:40:32

(which involves a couple ghcids, a ghci backend, and ghcjs building the frontend)

bennofs 2017-02-27 05:41:21

Cale: probably most of the memory is needed for GHC?

bennofs 2017-02-27 05:41:21

Cale: GHCJS i meant

Cale 2017-02-27 05:41:25

I usually just ssh to my desktop which has 64 GB

massprog 2017-02-27 05:41:39

where haskell should be used?

Cale 2017-02-27 05:41:39

Well, the ghcids each take quite a bit.

juri_ 2017-02-27 05:41:58

I just built a new one with 256GB of ram. runs out after 8 hours.

orion 2017-02-27 05:43:41

Cale: What are the other specifications of your desktop?

bennofs 2017-02-27 05:59:14

Guest82102: not an emacs expert. perhaps http://emacs.stackexchange.com/a/507 ?

Guest82102 2017-02-27 06:00:27

ah it locks on collecting type info

Cale 2017-02-27 06:00:27

So yeah, just checked, and my backend ghcid for this project is 2.1 GB, frontend one is 1.2 GB.

Guest82102 2017-02-27 06:00:27

thanks

Guest82102 2017-02-27 06:01:00

is 302 modules a lot?

Cale 2017-02-27 06:01:33

sorry, 1.6 rather than 1.2, it hadn't finished loading

Guest82102 2017-02-27 06:25:22

how can i debug linker errors?

paiv 2017-02-27 06:32:36

sup guys

nitrix 2017-02-27 06:33:05

Guest82102: Maybe publish/extract what you're working on and open a GHC ticket by providing them your test case.

nitrix 2017-02-27 06:33:56

Guest82102: If it's a linker error, chances are that other people stumbled on it too, so you might be able to find an existing ticket as well.

Guest82102 2017-02-27 06:33:57

nitrix, that's a method of debugging? lol

Guest82102 2017-02-27 06:36:15

that's not a debugging method - i'm asking how to get meaningful debug information from ghci other than linker error -1

nitrix 2017-02-27 06:37:07

Even the verbose mode of GHCi wont get you far.

Cale 2017-02-27 06:37:07

Guest82102: How are you causing that error to occur?

Guest82102 2017-02-27 06:37:19

loading my package into ghci

Guest82102 2017-02-27 06:37:27

then running main

Cale 2017-02-27 06:37:35

hmm

Guest82102 2017-02-27 06:37:39

the package builds successfully

Cale 2017-02-27 06:38:02

If you compile it to an executable and run it, that works okay?

Guest82102 2017-02-27 06:38:18

it croaks for a different reason (the one i'm trying to debug in ghci)

Guest82102 2017-02-27 06:38:22

so i don't know

AndreasK 2017-02-27 06:38:46

bollu: Probably didn't get accepted

nitrix 2017-02-27 06:38:50

Assuming it's really a linker error (which is the only information you provided to me), then my only recommendation is to let the people that knows best about the linker to solve it. These things have plenty of interractions and it's not something we can trivially solve over IRC.

Cale 2017-02-27 06:39:18

I've never seen a linker error which looked like "linker error -1"

nitrix 2017-02-27 06:39:51

Cale: The information so far: gcc: error: /tmp/ghc26073_0/ghc_331.o: No such file or directory

Guest82102 2017-02-27 06:40:15

$- :main

Guest82102 2017-02-27 06:40:16

gcc: error: /tmp/ghc26890_0/ghc_331.o: No such file or directory

Guest82102 2017-02-27 06:40:16

phase `Linker' failed (exitcode = 1)

bollu 2017-02-27 06:40:39

AndreasK: ouch, that's a little sad

Cale 2017-02-27 06:41:33

What is your module's filename?

Guest82102 2017-02-27 06:42:00

Cale, Main

Cale 2017-02-27 06:42:56

"Main.hs"?

Guest82102 2017-02-27 06:43:27

yes main is Main.hs

Cale 2017-02-27 06:43:41

okay

Guest82102 2017-02-27 07:02:29

and my question after all is what in the world is the point

nitrix 2017-02-27 07:04:25

I'm don't think I'm the right person to solve your existantial programmer crisis :P

nitrix 2017-02-27 07:05:13

But I can look at the GHC problem to improve it.

Guest82102 2017-02-27 07:07:27

i'm sorry i'm just waxing poetical after the argument i had with all of those people on r/haskell yesterday

monochrom 2017-02-27 07:09:06

This is why I stay away from reddit

kgadek 2017-02-27 07:09:06

Guest36413: oh, was that your topic there?

kgadek 2017-02-27 07:09:06

Sorry to hear you're disappointed

kgadek 2017-02-27 07:09:06

Or angry

mnoonan 2017-02-27 07:09:06

Guest82102: I have to admit, some of the things mentioned in your post sound like you might just have a borderline-insane codebase that you inherited.

Guest82102 2017-02-27 07:09:06

i'm not angry

Guest82102 2017-02-27 07:09:06

like i said i wanted to love haskell

Guest82102 2017-02-27 07:09:06

i'm annoyed

kgadek 2017-02-27 07:09:06

Ye, Haskell can do that. Especially at the beginning and then even for some time more

nitrix 2017-02-27 07:09:06

Keep in mind the issue you're having is with GHC. Haskell isn't responsible for this.

Guest82102 2017-02-27 07:09:06

programming languages are an ecosystem

kgadek 2017-02-27 07:09:06

nitrix: I don't agree. GHC is the de facto compiler of Haskell

Guest82102 2017-02-27 07:09:06

some of my complaints were about cabal/stack

cobreadmonster 2017-02-27 07:09:06

No Haskell at GSoC this year? :(

nitrix 2017-02-27 07:09:17

I see. It is trying to create a postgres DB at compile-time.

nitrix 2017-02-27 07:09:20

That's naughty.

kgadek 2017-02-27 07:09:44

nitrix: why as a user should I care? GHC's problems are Haskell problems. Nobody actually cares about details. YES, GNU/Linux and not Linux. I don't care

Guest82102 2017-02-27 07:09:48

how do i paste into emacs with evil mode?

mnoonan 2017-02-27 07:10:08

It's kind of hilarious to have shenanigans like that in your build, when your language is so principled about side-effects

Guest82102 2017-02-27 07:10:26

mnoonan, yes!

kgadek 2017-02-27 07:10:41

Agree on shenanigans

Cale 2017-02-27 07:10:49

nitrix: Yeah, that's really stupid imo, but I'm not going to question it for now ;)

mnoonan 2017-02-27 07:11:19

maybe the theory is to move all side-effects into the build, for ultimate run-time purity :)

Guest82102 2017-02-27 07:11:24

haha

nitrix 2017-02-27 07:12:04

kgadek: I cannot have this discussion right now, but I'll still say that you're missing the point. There are plenty of great and bad languages depending on different design decisions. Each affects the final product. Same with compiler development. Thing is, you're able to able amazing languages and bad compilers, or great compilers and shitty languages.

nitrix 2017-02-27 07:13:43

kgadek: Bundling the two is just disrespectful for the parties involved. Again, if GHC is what prevents someone from adopting Haskell, GHC gets improved and that's all.

Cale 2017-02-27 07:15:56

I suspect the problem here lies not even with GHC, but with this insane project's build setup

kgadek 2017-02-27 07:15:56

nitrix: ok, let's skip this discussion. But Haskell is not C++, we don't have 3 big compilers. We have one