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| 2024-11-20 19:23:25 +0100 | <bwe> | then loading that from DB, channelling it into different parsing machinery depending on `Variant`, which eventually culminates into `General` which is abstract, again |
| 2024-11-20 19:22:50 +0100 | euleritian | (~euleritia@ip4d16fc9f.dynamic.kabel-deutschland.de) (Ping timeout: 244 seconds) |
| 2024-11-20 19:22:31 +0100 | <tomsmeding> | right, so you're getting untyped data from the database, and you want to "create" more typing info? |
| 2024-11-20 19:22:09 +0100 | <bwe> | oh, storing multiple pages of different websites to a DB, differentiated by Variant |
| 2024-11-20 19:22:03 +0100 | <tomsmeding> | there are various ways something _like_ this can typecheck, but they all result in different designs of the program |
| 2024-11-20 19:21:29 +0100 | <tomsmeding> | what is the context? |
| 2024-11-20 19:21:23 +0100 | <tomsmeding> | where does DBEntry come from? |
| 2024-11-20 19:21:16 +0100 | <tomsmeding> | what is the X problem here (as in X-Y problem) :p |
| 2024-11-20 19:21:04 +0100 | <tomsmeding> | well, not really |
| 2024-11-20 19:20:52 +0100 | <tomsmeding> | no |
| 2024-11-20 19:20:39 +0100 | <bwe> | that would be type level programming, correct? |
| 2024-11-20 19:20:09 +0100 | <tomsmeding> | then the return type of fromDBEntry is linked to the _value_ inside the DBEntry |
| 2024-11-20 19:19:54 +0100 | <tomsmeding> | you could give Variant and DBEntry a type argument indicating what the variant is for (SiteA or SiteB) |
| 2024-11-20 19:19:34 +0100 | <tomsmeding> | the caller is allowed to choose a1 |
| 2024-11-20 19:19:29 +0100 | <tomsmeding> | same problem |
| 2024-11-20 19:19:17 +0100 | <bwe> | https://play-haskell.tomsmeding.com/saved/TXQ84gHu |
| 2024-11-20 19:19:01 +0100 | Unicorn_Princess | (~Unicorn_P@user/Unicorn-Princess/x-3540542) Unicorn_Princess |
| 2024-11-20 19:18:49 +0100 | <tomsmeding> | so this ain't going to work: _you_ want to choose, based on a value inside the DBEntry, what 'a' is, but the type signature of fromDBEntry allows the caller of fromDBEntry to choose 'a' |
| 2024-11-20 19:18:20 +0100 | <tomsmeding> | bwe: this is getting closer, but something else is still off: in fromDBEntry, you're deciding which variant to return based on siteVariant from the DBEntry, but the _type_ you hvae to return, 'a', is from that Dict (IntoGeneral a) argument |
| 2024-11-20 19:16:57 +0100 | <bwe> | (it's not compiling, ofc) |
| 2024-11-20 19:16:02 +0100 | <bwe> | so reversing DataKinds for a moment: https://play-haskell.tomsmeding.com/saved/eaWYsjTO |
| 2024-11-20 19:15:44 +0100 | tzh | (~tzh@c-76-115-131-146.hsd1.or.comcast.net) tzh |
| 2024-11-20 19:13:59 +0100 | <tomsmeding> | where SiteA and SiteB are actual data types with fields |
| 2024-11-20 19:13:54 +0100 | <tomsmeding> | bwe: are you perhaps confused because you actually intended to write `data SiteVariant = SiteA SiteA | SiteB SiteB`? |
| 2024-11-20 19:12:45 +0100 | ash3en | (~Thunderbi@2a03:7846:b6eb:101:93ac:a90a:da67:f207) ash3en |
| 2024-11-20 19:12:33 +0100 | <tomsmeding> | (if you're posting playground snippets, you can check them with a click on a button -- do so ;) ) |
| 2024-11-20 19:12:16 +0100 | <bwe> | so that will be then SiteVariant |
| 2024-11-20 19:12:15 +0100 | <tomsmeding> | this doesn't typecheck |
| 2024-11-20 19:11:57 +0100 | <tomsmeding> | still an 'a' left in the return type of fromHTML |
| 2024-11-20 19:11:43 +0100 | <bwe> | https://play-haskell.tomsmeding.com/saved/hi8Hh5MO |
| 2024-11-20 19:11:35 +0100 | <bwe> | tomsmeding: You got me :). |
| 2024-11-20 19:10:57 +0100 | <tomsmeding> | if you want to return the _constructor_ SiteA instead, it should be initSiteA :: SiteVariant |
| 2024-11-20 19:10:28 +0100 | <tomsmeding> | it is _impossible_ to write an initSiteA that is not undefined |
| 2024-11-20 19:10:14 +0100 | <tomsmeding> | that function has no definition |
| 2024-11-20 19:10:10 +0100 | <tomsmeding> | how are you going to write initSiteA? |
| 2024-11-20 19:09:57 +0100 | <bwe> | tomsmeding: https://play-haskell.tomsmeding.com/saved/dfb9mlT9 |
| 2024-11-20 19:09:31 +0100 | <tomsmeding> | SiteA is not a type of kind Type |
| 2024-11-20 19:09:22 +0100 | <tomsmeding> | ah with your latest paste, GHC complains as I expect |
| 2024-11-20 19:08:33 +0100 | <bwe> | so, I had three initiations recently: Proxy, Constraints / withDict and DataKinds |
| 2024-11-20 19:08:19 +0100 | <tomsmeding> | a _value of type SiteA_, to be precise? |
| 2024-11-20 19:08:09 +0100 | <tomsmeding> | how are you going to create a SiteA? |
| 2024-11-20 19:08:03 +0100 | euleritian | (~euleritia@ip4d16fc9f.dynamic.kabel-deutschland.de) |
| 2024-11-20 19:08:02 +0100 | <tomsmeding> | bwe: that 'a' return value from fromHTML is suspect |
| 2024-11-20 19:07:48 +0100 | euleritian | (~euleritia@dynamic-176-001-003-233.176.1.pool.telefonica.de) (Read error: Connection reset by peer) |
| 2024-11-20 19:07:32 +0100 | <tomsmeding> | I see, I haven't followed the discussion, just saw your last post :) |
| 2024-11-20 19:07:06 +0100 | <tomsmeding> | a type that has no values (because it's not a type of kind Type), hence you can't ask for a value of it in the type of fromHTML |
| 2024-11-20 19:07:02 +0100 | <bwe> | tomsmeding: yup, but I've started out using withDict before dminuoso proposed to switch to DataKinds |
| 2024-11-20 19:06:26 +0100 | <tomsmeding> | that SiteA there is in the position where a type is expected, but it's a data constructor; DataKinds lifts it to a type |
| 2024-11-20 19:06:06 +0100 | <tomsmeding> | bwe: the moment you write `IntoGeneral SiteA` you're using DataKinds |
| 2024-11-20 19:06:03 +0100 | euleritian | (~euleritia@dynamic-176-001-003-233.176.1.pool.telefonica.de) |