Parsing forms suggestion for Dashdo project

ParseForm.hs

{-# LANGUAGE OverloadedStrings, ExistentialQuantification, ExtendedDefaultRules, FlexibleContexts, Rank2Types, TemplateHaskell #-}
module Demo where

import Data.Monoid ((<>))
import Lens.Micro.Platform

data ExampleParams = ExampleParams
 { _foo :: Int
 , _bar :: [Int]
 } deriving (Show)

makeLenses ''ExampleParams

parseForm :: a -> [(Int, (a -> String -> a))] -> [(String, String)] -> a
parseForm x [] _ = x
parseForm x ((n,f):nfs) pars =
  let fldName = "f"<> (show n)
      newx = case lookup fldName pars of
                Just lt -> f x lt
                Nothing -> case filter ((== fldName <> "[]") . fst) pars of
                  []         -> x
                  listParams -> foldl f x (map snd listParams)
  in parseForm newx nfs pars

fooUpdater :: ExampleParams -> String -> ExampleParams
fooUpdater ep s = set foo (read s :: Int) $ ep

barUpdater :: ExampleParams -> String -> ExampleParams
barUpdater ep s = over bar ((:) (read s :: Int)) $ ep

handlers = [(0, fooUpdater), (1, barUpdater)]

queryParams = [("f0", "100"), ("f1[]", "900"), ("f1[]", "1000"), ("f1[]", "2000")]

main = parseForm (ExampleParams 0 []) handlers queryParams

{-
> main
ExampleParams {_foo = 100, _bar = [2000,1000,900]}
-}