scala - Mapping over a JSON array with Argonaut -

i'm having hard time slogging through argonaut documentation, figured i'd ask simple example.

val input = """{"a":[{"b":4},{"b":5}]}"""  val output = ??? // desired value: list(4, 5) 

i can cursor down array:

parse.parse(input).map((jobjectpl >=> jsonobjectpl("a") >=> jarraypl)(_)) // scalaz.\/[string,option[scalaz.indexedstore[argonaut.argonaut.jsonarray, //  argonaut.argonaut.jsonarray,argonaut.json]]] = // \/-(some(indexedstoret((<function1>,list({"b":4}, {"b":5}))))) 

but what? on right track? should using cursors this?

edit - here's progress, guess. i've written decoder list:

parse.parse("""[{"b": 4}, {"b": 5}]""")   .map(_.as(ilistdecodejson(decodejson(_.downfield("b").as[int])))) // scalaz.\/[string,argonaut.decoderesult[scalaz.ilist[int]]] = // \/-(decoderesult(\/-([4,5]))) 

edit - starting put together...

parse.parse(input).map(_.as[hcursor].flatmap(_.downfield("a").as(   ilistdecodejson(decodejson(_.downfield("b").as[int]))))) // scalaz.\/[string,argonaut.decoderesult[scalaz.ilist[int]]] = // \/-(decoderesult(\/-([4,5]))) 

edit - guess best solution far is:

parse.parse(input).map(_.as(   decodejson(_.downfield("a").as(     ilistdecodejson(decodejson(_.downfield("b").as[int])).map(_.tolist)   )) )) 

feels bit verbose, though.

you can pretty nicely new-ish monocle support in argonaut (i'm using argonaut master here, since 6.1 milestones still on monocle 0.5):

import argonaut._, argonaut._ import scalaz._, scalaz._ import monocle._, monocle._  val lens =   parse.parseoptional ^<-?    jobjectprism        ^|-?   index("a")          ^<-?   jarrayprism         ^|->>   each                ^<-?   jobjectprism        ^|-?   index("b")          ^<-?   jintprism 

and then:

scala> lens.getall("""{"a":[{"b":4},{"b":5}]}""") res0: scalaz.ilist[int] = [4,5] 

the operators horrible @ first, used them, , composed pieces read pretty naturally. , of course since lens there kinds of operations can use in addition getall.