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danidiaz/IsRecord.hs

Last active August 12, 2017 09:52
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IsRecord constraint using generics-sop type-level metadata. Related to https://gist.github.com/danidiaz/3f396f92a6dda1cff87639ec4f1194df
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IsRecord.hs
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE TypeFamilies #-}
module Soapy (IsRecord) where
import GHC.TypeLits (Symbol)
import Generics.SOP
import qualified Generics.SOP.Type.Metadata as T
type IsRecord (r :: *) (mn :: Symbol) (dn :: Symbol) (cn :: Symbol) (fs :: [T.FieldInfo]) (xs :: [*]) =
(IsProductType r xs, DatatypeInfoOf r ~ T.ADT mn dn '[T.Record cn fs], T.DemoteFieldInfos fs xs)
-- Use T.demoteFieldInfos to get a n-ary product with the names of the constructors.
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