How to parse a list of Json objects in Haskell? -

i have data class:

data mydata = mydata { :: int, b :: string } instance tojson mydata   ....  instance fromjson mydata   .... 

i can parse single object json:

get :: io (maybe mydata) =   res <- getsingleitemhttp   return $ decode $ responsebody res 

how can list of mydata?

get2 :: io [mydata] get2 =       res <- getmanyitemshttp        --????       return $ decode $ responsebody res -- doesn't compile 

how go parsing responsebody list?

it should work once pass in array (and decode list) have change signature get2 :: io (maybe [mydata]):

{-# language derivegeneric, overloadedstrings #-} module json  import ghc.generics import data.aeson import data.text import data.bytestring.lazy  data mydata = mydata { :: int, b :: string }   deriving (generic, show)  instance fromjson mydata  example :: bytestring example = "[{ \"a\": 1, \"b\": \"hello\" }, { \"a\": 2, \"b\": \"world\" }]" 

example

λ> decode example :: maybe [mydata] [mydata {a = 1, b = "hello"},mydata {a = 2, b = "world"}] 

---

your problem

would this: if try

get :: [mydata] = decode example 

the compiler complain with

couldn't match expected type [mydata] actual type maybe a0 …

which should give big hint.

you can still signature data.maybe.maybetolist:

get :: [mydata] = prelude.concat . maybetolist $ decode example