Lens.hs

{-# LANGUAGE NoImplicitPrelude #-}

{-|
Module      : Headroom.Data.Lens
Description : Custom functionality related to /lens/
Copyright   : (c) 2019-2020 Vaclav Svejcar
License     : BSD-3-Clause
Maintainer  : vaclav.svejcar@gmail.com
Stability   : experimental
Portability : POSIX

Provides customized versions of /lens/ functions.
-}

module Headroom.Data.Lens
  ( suffixLenses
  , suffixLensesFor
  )
where

import qualified Language.Haskell.TH.Lib       as TH
import qualified Language.Haskell.TH.Syntax    as TH
import           Lens.Micro.TH                  ( DefName(..)
                                                , lensField
                                                , lensRules
                                                , lensRulesFor
                                                , makeLensesWith
                                                )
import           RIO


-- | A template haskell function to build lenses for a record type. This
-- function differs from the 'Control.Lens.makeLenses' function in that
-- it does not require the record fields to be prefixed with underscores
-- and it adds an "L" suffix to lens names to make it clear that they
-- are lenses.
suffixLenses :: TH.Name -> TH.DecsQ
suffixLenses = makeLensesWith $ lensRules & lensField .~ withSuffix
  where withSuffix _ _ name = [TopName . TH.mkName $ (TH.nameBase name <> "L")]


-- | Same as 'suffixLensesFor', but build lenses only for selected fields.
suffixLensesFor :: [String] -> TH.Name -> TH.DecsQ
suffixLensesFor fields = makeLensesWith $ lensRulesFor fields'
  where fields' = fmap (\f -> (f, f <> "L")) fields