[Haskell-cafe] help with type variable escaping scope/passing lens as function argument

[Cody Goodman]

I have the following code and error(also seen at
https://github.com/codygman/frames-credit-card-trans-demo/blob/master/src/Main.hs#L28
):


-- between meaning on or after start but before end
dateBetween :: _
            -> Day
            -> Day
            -> Pipe (Record rs) (Record rs) IO r
dateBetween target start end = P.filter go
  where go :: Record rs -> _
        go r = let targetDate = rget target r :: Chicago
                   targetDate' = chicagoToZoned targetDate :: ZonedTime
                   targetDay = localDay (zonedTimeToLocalTime targetDate')
:: Day
               in
                 targetDay >= start && targetDay < end
-- type error
-- src/Main.hs:48:38: error: …
--     • Couldn't match expected type ‘(Chicago -> f Chicago)
--                                     -> Record rs1 -> f (Record rs1)’
--                   with actual type ‘t’
--         because type variable ‘f’ would escape its scope
--       This (rigid, skolem) type variable is bound by
--         a type expected by the context:
--           Functor f => (Chicago -> f Chicago) -> Record rs1 -> f (Record
rs1)
--         at
/home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:33-45
--     • In the first argument of ‘rget’, namely ‘target’
--       In the expression: rget target r :: Chicago
--       In an equation for ‘targetDate’:
--           targetDate = rget target r :: Chicago
--     • Relevant bindings include
--         r :: Record rs1
--           (bound at
/home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:12)
--         go :: Record rs1 -> Bool
--           (bound at
/home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:9)
--         target :: t
--           (bound at
/home/cody/source/frames-credit-card-trans-demo/src/Main.hs:46:13)
--         dateBetween :: t -> Day -> Day -> Pipe (Record rs) (Record rs)
IO r
--           (bound at
/home/cody/source/frames-credit-card-trans-demo/src/Main.hs:46:1)
-- Compilation failed.

Perhaps it's late, but I'm fairly sure I've done something like this before.

Thanks,

Cody
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