Logs: liberachat/#haskell
| 2021-06-22 14:51:30 | × | wallymathieu quits (~wallymath@81-234-151-21-no94.tbcn.telia.com) (Quit: My MacBook has gone to sleep. ZZZzzz…) |
| 2021-06-22 14:51:31 | <Guest31> | operable program or batch file. |
| 2021-06-22 14:51:31 | <Guest31> | make: *** [Makefile:22: ghci] Error 1 |
| 2021-06-22 14:52:24 | <Guest31> | if anyone could help with this it would be greatly appreciated; I'm trying to get this to work on a windows 10 machine for reference. Am a haskell beginner trying to do the fp-course |
| 2021-06-22 14:52:42 | → | nerdypepper joins (~nerdypepp@user/nerdypepper) |
| 2021-06-22 14:52:50 | <Las[m]> | This isn't really a solution, but I suggest you'd really do all development through WSL |
| 2021-06-22 14:53:34 | × | derelict quits (~derelict@user/derelict) (Quit: WeeChat 3.2) |
| 2021-06-22 14:54:24 | <Las[m]> | Does anyone know why you can't call into Haskell again from an unsafe foreign call? |
| 2021-06-22 14:54:59 | <jiribenes> | Guest31: maybe try first setting the variable, 'SET STACK_YAML="stack.yaml"' and then run 'stack ghci course:lib'? |
| 2021-06-22 14:55:09 | <merijn> | Las[m]: Because the capability is locked |
| 2021-06-22 14:56:08 | <Las[m]> | merijn: Thanks that makes sense |
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| 2021-06-22 14:57:05 | <Guest31> | jiribenes: do you mean setting an environment variable? sorry i'm really new and not sure where i should change this setting |
| 2021-06-22 14:58:21 | <jiribenes> | Guest31: try first writting the command 'SET STACK_YAML="stack.yaml"' to the command line |
| 2021-06-22 14:58:32 | <jiribenes> | and after that write 'stacj ghci course:lib' |
| 2021-06-22 14:58:42 | <jiribenes> | sorry, 'stack ghci course:lib' |
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| 2021-06-22 14:58:54 | <Guest31> | Getting project config file from STACK_YAML environment |
| 2021-06-22 14:58:54 | <Guest31> | InvalidAbsFile "D:\\Documents\\GitHub\\fp-course\\\"stack.yaml\"" |
| 2021-06-22 14:59:11 | <Guest31> | i just tried that; it then gives me this error |
| 2021-06-22 14:59:50 | <jiribenes> | maybe try setting it without the quote marks, that is 'SET STACK_YAML=stack.yaml' |
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| 2021-06-22 15:00:59 | <Guest31> | jiribenes: it worked!! thank you so much |
| 2021-06-22 15:03:33 | <Guest31> | can I also ask if anyone knows where stack downloads its files? and if its possible to change this. Reading through the documentation it sounded like stack downloads a local copy of ghc for each project? i'm not sure if i understood correctly |
| 2021-06-22 15:04:08 | <Guest31> | not really an issue at present; but in general if stack sets up and downloads files for me to do things, i was hoping to check where the downloaded files go |
| 2021-06-22 15:05:25 | <Boarders> | Does anyone know if in a stack yaml file if I can overwrite a $everything flag with a $locals flag, e.g. if I pass `-O2` to $everything and -O1 to $locals then which one wins? |
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| 2021-06-22 15:20:38 | <safinaskar> | % proof :: forall (a :: *). (forall (x :: a). x :~: x) -> (forall (x :: a). x :~: x); proof = error "" |
| 2021-06-22 15:20:38 | <yahb> | safinaskar: ; <interactive>:49:93: error:; * Couldn't match expected type `(forall (x :: a). x :~: x) -> forall (x :: a). x :~: x' with actual type `a0'; Cannot instantiate unification variable `a0'; with a type involving polytypes: (forall (x :: a). x :~: x) -> forall (x :: a). x :~: x; * In the expression: error ""; In an equation for `proof': proof = error ""; * Relevant bindings inc |
| 2021-06-22 15:20:48 | <safinaskar> | why this gives compilation error? |
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| 2021-06-22 15:26:27 | <c_wraith> | safinaskar: the error message seems pretty specific "Cannot instantiate unification variable `a0'; with a type involving polytypes:" |
| 2021-06-22 15:27:17 | <c_wraith> | safinaskar: that particular case might seem obvious, but the larger technique is not |
| 2021-06-22 15:27:32 | <safinaskar> | c_wraith: okey, but how this is possible that (error "") cannot match with (proof)? (error) has type (forall a. String -> a) |
| 2021-06-22 15:27:47 | <safinaskar> | c_wraith: so (error "") should match with everything, right? |
| 2021-06-22 15:28:33 | <c_wraith> | safinaskar: because it needs to unify the type of (error "") with the type you provided |
| 2021-06-22 15:28:52 | <lyxia> | "forall a" does not mean a can literally be anything in existence. |
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| 2021-06-22 15:29:04 | <c_wraith> | safinaskar: and that unification fails because it would require a polytype |
| 2021-06-22 15:29:17 | <lyxia> | there is a range of things a can be, and polytypes are not among them. |
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| 2021-06-22 15:29:36 | <c_wraith> | safinaskar: What version of GHC are you using? |
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| 2021-06-22 15:30:41 | <safinaskar> | c_wraith: 9.2.0.20210422 (latest which can be installed using ghcup) |
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| 2021-06-22 15:31:05 | <c_wraith> | do you have -XImpredicativeTypes on? |
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| 2021-06-22 15:31:58 | <c_wraith> | I'm not sure about the limits of the new implementation for it. It *might* be able to handle this case. |
| 2021-06-22 15:32:39 | <safinaskar> | c_wraith: lyxia: thanks, what are polytypes? |
| 2021-06-22 15:33:33 | <safinaskar> | c_wraith: i didn't have ImpredicativeTypes . now i enabled it, and the code works. thanks! |
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| 2021-06-22 15:34:14 | <c_wraith> | a polytype is essentially a type with a forall anywhere other than the top level |
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| 2021-06-22 15:35:03 | <c_wraith> | (I'm sure you could find some counterexamples that you need a more precise definition to deal with, but that's a good starting point) |
| 2021-06-22 15:35:14 | <lyxia> | (short for "types with polymorphism") |
| 2021-06-22 15:38:48 | <c_wraith> | In any case, -XImpredicativeTypes exists specifically to allow unification to work with polytypes |
| 2021-06-22 15:39:07 | <c_wraith> | It has some limits - you can get sophisticated enough that it gives up. |
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| 2021-06-22 15:41:27 | <monochrom> | IIRC 9.2 uses what's on the QuickLook impredicavity paper, so it is fairly well-defined what it tries. |
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| 2021-06-22 15:43:46 | <c_wraith> | yeah, I just don't know what the limits are - I haven't read the paper. |
| 2021-06-22 15:44:00 | <monochrom> | Ha nice ghcup knows 9.2 prerelease. |
| 2021-06-22 15:47:52 | <monochrom> | The nice thing is if you don't know, but you have had experience and good habits in handwriting type sigs for ordinary Haskell code, you won't be surprised about where you need to handwrite types. |
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| 2021-06-22 15:48:22 | <monochrom> | A long way to say "intuitive" but it's a vague and much abused word. |
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| 2021-06-22 16:01:59 | <tomsmeding> | % proof :: forall (a :: *). (forall (x :: a). x :~: x) -> (forall (x :: a). x :~: x); proof _ = error "" |
| 2021-06-22 16:01:59 | <yahb> | tomsmeding: |
| 2021-06-22 16:02:13 | <tomsmeding> | (added a _ argument) |
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