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