Haskell Channel Logs: #haskell channel featuring magthe, opqdonut, liste, jle`, recur22, ibrahemgebri, and 8 others.

qmm 2017-02-05 19:57:31

http://lpaste.net/352119 forkProcess :: LocalNode -> Process () -> IO ProcessId ; run :: Port -> Application -> IO () ; how to turn IO () into a Process ()? https://hackage.haskell.org/package/distributed-process-0.6.6/docs/Control-Distributed-Process-Internal-Types.html#t:Process derives a MonadIO

liste 2017-02-05 19:58:26

:t liftIO

lambdabot 2017-02-05 19:58:27

MonadIO m => IO a -> m a

liste 2017-02-05 19:58:38

qmm: ^

magthe 2017-02-05 19:59:11

is there no IRC channel for stack/stackage discussions?

jle` 2017-02-05 19:59:37

magthe: there's #haskell-stack

magthe 2017-02-05 20:00:05

jle`: aha... I'll see about adding it to the wiki then :) thanks!

jle` 2017-02-05 20:00:15

no problem!

marekw2143 2017-02-05 20:09:18

hello, in case of code: "data SuperData a = SuperData { runSuperData :: Maybe a }

marekw2143 2017-02-05 20:09:23

then what is runSuperData /

marekw2143 2017-02-05 20:09:24

srhb 2017-02-05 20:09:50

marekw2143: It says what it is right there in the type of the field, it's a Maybe a

marekw2143 2017-02-05 20:10:35

oh, so "superData" is just a field -generally it's field syntax constructor ?

srhb 2017-02-05 20:11:07

marekw2143: There is no superData. SuperData is a value constructor though. Not a field.

srhb 2017-02-05 20:11:14

marekw2143: runSuperData is a field.

marekw2143 2017-02-05 20:11:29

yes, I've meant runSuperData

srhb 2017-02-05 20:11:42

Then yes, it's a field. :)

marekw2143 2017-02-05 20:13:12

but here https://github.com/kqr/gists/blob/master/articles/gentle-introduction-monad-transformers.md#type-classes

marekw2143 2017-02-05 20:13:17

then there's rfield runEitherIO

marekw2143 2017-02-05 20:13:25

but I cannot see it's definitio

srhb 2017-02-05 20:13:44

marekw2143: It has no "definition" beyond that.

marekw2143 2017-02-05 20:14:10

so how it works ?

srhb 2017-02-05 20:14:19

marekw2143: If you make a _value_ of type EitherIO e a, you would _provide_ an IO (Either e a)

dramforever 2017-02-05 20:14:27

@let data SuperData a = SuperData { runSuperData :: Maybe a }

lambdabot 2017-02-05 20:14:28

Defined.

dramforever 2017-02-05 20:14:30

:t runSuperData

lambdabot 2017-02-05 20:14:32

SuperData a -> Maybe a

srhb 2017-02-05 20:14:36

marekw2143: It doesn't "work." I think you're confused by the "run" in the name.

dramforever 2017-02-05 20:14:54

it just gets the 'Maybe a' out of a SuperData

dramforever 2017-02-05 20:15:00

:t SuperData

lambdabot 2017-02-05 20:15:05

Maybe a -> SuperData a

dramforever 2017-02-05 20:15:09

^ basically the reverse of this

marekw2143 2017-02-05 20:15:25

hmm, it seems like just pattern matching

dramforever 2017-02-05 20:15:30

You know record syntax?

marekw2143 2017-02-05 20:15:37

I thought I know

marekw2143 2017-02-05 20:15:38

;)

dramforever 2017-02-05 20:15:46

@let data Point = Point { x :: Double, y :: Double }

lambdabot 2017-02-05 20:15:48

Defined.

dramforever 2017-02-05 20:15:51

:t x

lambdabot 2017-02-05 20:15:52

error:

lambdabot 2017-02-05 20:15:52

Ambiguous occurrence 'x'

lambdabot 2017-02-05 20:15:52

It could refer to either 'Debug.SimpleReflect.x',

dramforever 2017-02-05 20:15:56

Exactly the same here

dramforever 2017-02-05 20:16:05

except I've got another stupid x interfering here

marekw2143 2017-02-05 20:16:20

ok, so in runEitherIO example

dramforever 2017-02-05 20:16:22

@let data BetterPoint = BetterPoint { betterx :: Double, bettery :: Double }

lambdabot 2017-02-05 20:16:23

Defined.

dramforever 2017-02-05 20:16:27

:t betterx

lambdabot 2017-02-05 20:16:28

BetterPoint -> Double

marekw2143 2017-02-05 20:16:30

thne runEitherIO is just a function

marekw2143 2017-02-05 20:16:40

which on the basis of instance EitherIO a e

dramforever 2017-02-05 20:16:47

no basis

dramforever 2017-02-05 20:17:04

oops sorry

dramforever 2017-02-05 20:17:12

marekw2143: What do you mean by basis?

marekw2143 2017-02-05 20:17:40

by "on basis" I mean that having "value of type EitherIO a e"

dramforever 2017-02-05 20:17:52

okay

marekw2143 2017-02-05 20:17:58

so that runEitherIO just unpacks "value of type EitherIO a e"

marekw2143 2017-02-05 20:18:09

to value of type IO (Either a e )

dramforever 2017-02-05 20:18:09

exactly

marekw2143 2017-02-05 20:18:23

so it' s just something like pattern mathicnng ?

dramforever 2017-02-05 20:18:47

('IO (Either e a)' really)

dramforever 2017-02-05 20:19:14

Yeah

dramforever 2017-02-05 20:19:19

Just how records work

marekw2143 2017-02-05 20:19:27

dramforever 2017-02-05 20:19:31

It's kinda like a trick or something

marekw2143 2017-02-05 20:19:35

but how to set that value to it ?

dramforever 2017-02-05 20:19:49

EitherIO is a constructor :P

dramforever 2017-02-05 20:19:54

:t EitherIO

lambdabot 2017-02-05 20:19:56

error: Data constructor not in scope: EitherIO

dramforever 2017-02-05 20:20:08

oh, we've got SuperData

dramforever 2017-02-05 20:20:11

:t SuperData

lambdabot 2017-02-05 20:20:12

Maybe a -> SuperData a

dramforever 2017-02-05 20:20:24

That's how to 'set that value to it'

dramforever 2017-02-05 20:20:44

For record syntax you would probably normally do this:

dramforever 2017-02-05 20:20:53

:t BetterPoint { x = 1, y = 2 }

lambdabot 2017-02-05 20:20:54

error:

lambdabot 2017-02-05 20:20:54

Ambiguous occurrence 'x'

lambdabot 2017-02-05 20:20:54

It could refer to either 'Debug.SimpleReflect.x',

dramforever 2017-02-05 20:21:02

:t BetterPoint { betterx = 1, bettery = 2 }

lambdabot 2017-02-05 20:21:04

BetterPoint

dramforever 2017-02-05 20:21:09

Sorry, the second one is correct

dramforever 2017-02-05 20:21:16

But this works just fine:

dramforever 2017-02-05 20:21:23

:t BetterPoint 1 2

lambdabot 2017-02-05 20:21:25

BetterPoint

dramforever 2017-02-05 20:21:35

> betterx (BetterPoint 1 2) -- You can even get the x out of it

lambdabot 2017-02-05 20:21:38

1.0

dramforever 2017-02-05 20:21:46

but it kinda defeats the purpose of records

marekw2143 2017-02-05 20:21:53

ok, so in example with "EitherIO"

dramforever 2017-02-05 20:21:59

*but* for EitherIO we *know* we have only one field

dramforever 2017-02-05 20:22:07

so it's not going to be any trouble

dramforever 2017-02-05 20:22:10

it's actually easier to do

dramforever 2017-02-05 20:22:22

so I called it sorta a trick above

marekw2143 2017-02-05 20:22:29

marekw2143 2017-02-05 20:23:10

so when I'd have value1 = EitherIo { runEitherIod = IO ( Either 1 "error" } }

marekw2143 2017-02-05 20:23:16

that is the way ?

dramforever 2017-02-05 20:23:28

That's one way

dramforever 2017-02-05 20:23:45

'the' way is usually just 'EitherIO something'

dramforever 2017-02-05 20:24:01

And you are confusing types and values in your construction as well

halogenandtoast 2017-02-05 20:24:10

Anyone here from Tokyo?

dramforever 2017-02-05 20:24:20

'IO ( Either 1 "error")' makes no sense

marekw2143 2017-02-05 20:24:44

because 1 and "error" are values

pikajude 2017-02-05 20:25:16

well they could be Nat and Symbol

pikajude 2017-02-05 20:25:18

or whatever those are called

dramforever 2017-02-05 20:25:36

marekw2143: then what are your IO and Either doing there?

dramforever 2017-02-05 20:25:46

pikajude: go away you're ruining the fun

marekw2143 2017-02-05 20:27:29

hmm, so in example with monad transformers

marekw2143 2017-02-05 20:27:59

for definition of monad like x >>= f = EitherIO $ runEitherIO x >>= either (return .Left) (runEitherIO . f)

recur22 2017-02-05 20:28:14

dose anyone here know if diagrams support hittesting?i tried to google it but no luck

marekw2143 2017-02-05 20:28:46

then first "runEitherIO x" just gives us value of IO (Eitther a e)

marekw2143 2017-02-05 20:29:23

then there's used ">>=" defined for IO monad ?

ertes 2017-02-05 20:31:31

the API of System.Mem.StableName is confusing… why does StableName have a type argument, and why does makeStableName take a value of that type?

marekw2143 2017-02-05 20:31:31

:t either

lambdabot 2017-02-05 20:31:33

(a -> c) -> (b -> c) -> Either a b -> c

ertes 2017-02-05 20:31:43

isn't it basically equivalent to Data.Unique?

ertes 2017-02-05 20:34:57

ah, i see

ertes 2017-02-05 20:35:07

it does actually take sharing into account

ertes 2017-02-05 20:37:25

yet i don't see why StableName would require a type argument

opqdonut 2017-02-05 20:40:13

ertes: yeah it's not really used for anything, except to limit the Eq instance to the same type

ertes 2017-02-05 20:40:42

opqdonut: even that is questionable since there is eqStableName, which doesn't have that limit

opqdonut 2017-02-05 20:41:49

maybe the answer is that GHC.Base.StableName# takes a type argument