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Documentation of Haskell libraries #haskell #lantern

๐Ÿ•œ๏ธŽ - 2021-10-09

While I was improving Lantern I wanted to use the Haskell library Database.PostgreSQL.Simple.Notification to monitor update search index events.

I was a little confused when I read the documentation of getNotification and saw that it didn't take what channel to listen on as an argument - having just read the PostgreSQL documentation of NOTIFY channel + LISTEN channel that was what I was expecting.

After some digging I found a test for the library and from that saw that the way to use D.P.S.Notification is to execute one or more LISTEN channel before calling getNotification.

In hindsight it is obvious (you want to be able to listen to multiple channels in the same getNotification call), but to me, as a relative beginner in Haskell and using postgresql-simple, and never having tried LISTEN/NOTIFY before, it wasn't.

I have written to the maintainer and suggested that the documentation of D.P.S.Notification mention this.

One thing I miss in the documentation of many Haskell libraries is a couple of lines giving an example of how to use them - luckily I found the solution in a test this time.

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