Support Text and Int in Envy

src/Envy.hs

@@ -2,6 +2,7 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
 
 module Envy
   ( type (=@@)
@@ -22,13 +23,16 @@ import Data.Char (isLower, isUpper, toUpper)
 import Data.Kind (Type)
 import Data.Proxy (Proxy (..))
 import Data.Ratio ((%))
+import Data.Text (Text)
 import Data.Typeable (Typeable, typeRep)
 import GHC.Generics (C, D, Generic, K1 (..), M1 (..), Meta (..), Rec0, Rep, S, to, (:*:) (..))
-import GHC.TypeLits (KnownNat, KnownSymbol, natVal, symbolVal)
+import GHC.TypeLits (KnownNat, KnownSymbol, natVal, symbolVal, type (<=))
 import System.Environment (getEnvironment)
 import Text.Printf (printf)
 import Text.Read (readEither)
 
+import qualified Data.Text as Text
+
 data ConfigVariant = Spec | Value
 
 data Required t
@@ -113,15 +117,30 @@ class ProvidesDefault t d where
 instance ReadEnvVar Integer where
   readEnvVar = readEither
 
+-- TODO: Support negative integers (e.g. (Negate n))
 instance (KnownNat n) => ProvidesDefault Integer n where
   getDefault Proxy = natVal (Proxy @n)
 
+instance ReadEnvVar Int where
+  readEnvVar = readEither
+
+-- TODO: Support negative integers (e.g. (Negate n))
+-- This instance assumes that @Int@ is a 64-bit integer and enforces its range on the type level.
+instance (KnownNat n, n <= 9223372036854775807) => ProvidesDefault Int n where
+  getDefault Proxy = fromInteger $ natVal (Proxy @n)
+
 instance ReadEnvVar String where
   readEnvVar = Right
 
 instance (KnownSymbol s) => ProvidesDefault String s where
   getDefault Proxy = symbolVal (Proxy @s)
 
+instance ReadEnvVar Text where
+  readEnvVar = fmap Text.pack . readEnvVar
+
+instance (KnownSymbol s) => ProvidesDefault Text s where
+  getDefault Proxy = Text.pack $ getDefault (Proxy @s)
+
 instance ReadEnvVar Rational where
   readEnvVar = readEither