Put witness class somewhere more central and add all instances

byg/src/Function.hs

@@ -1,5 +1,4 @@
 {-# LANGUAGE GADTs #-}
-{-# LANGUAGE FunctionalDependencies #-}
 module Function
   ( concatStrings
   , concatTexts
@@ -17,7 +16,7 @@ module Function
 import Prelude hiding (String, FilePath)
 
 import Types.Values
-import Types.Value (Valuable)
+import Types.Value (Valuable, WitnessFor(..))
 import Types.Function
 import Types.Token (Token(..))
 import DependencyGenerator (DepGenM, TokenableTo(..), toTupleToken, runFunction)
@@ -78,12 +77,6 @@ lowerString :: TokenableTo String a => a -> DepGenM (Token String)
 lowerString a = runFunction LowerString =<< toToken a
 
 
-class (Show w, Lift w) => WitnessFor w t | w -> t, t -> w where
-  witnessValue :: w
-
-data StringType = StringType deriving (Show, Lift)
-instance WitnessFor StringType String where witnessValue = StringType
-
 data ElemOf a where ElemOf :: WitnessFor w a => w -> ElemOf a
 deriving instance Show (ElemOf a)
 deriving instance Lift (ElemOf a)

byg/src/Types/Value.hs

@@ -1,6 +1,9 @@
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE FunctionalDependencies #-}
 module Types.Value
   ( Value(..)
   , Valuable(..)
+  , WitnessFor(..)
   ) where
 
 import Prelude hiding (String)
@@ -86,3 +89,34 @@ instance Valuable a => Valuable [a] where
   fromValue = \case
     List a -> map fromValue a
     _ -> error "unexpected"
+
+
+class (Show w, Lift w) => WitnessFor w t | w -> t, t -> w where
+  witnessValue :: w
+
+data StringType = StringType deriving (Show, Lift)
+instance WitnessFor StringType String where witnessValue = StringType
+
+data TextType = TextType deriving (Show, Lift)
+instance WitnessFor TextType Text where witnessValue = TextType
+
+data BoolType = BoolType deriving (Show, Lift)
+instance WitnessFor BoolType Bool where witnessValue = BoolType
+
+data ImageType = ImageType deriving (Show, Lift)
+instance WitnessFor ImageType Image where witnessValue = ImageType
+
+data ImageConversionSettingsType = ImageConversionSettingsType deriving (Show, Lift)
+instance WitnessFor ImageConversionSettingsType ImageConversionSettings where witnessValue = ImageConversionSettingsType
+
+data TemplateType = TemplateType deriving (Show, Lift)
+instance WitnessFor TemplateType Template where witnessValue = TemplateType
+
+data EmptyType = EmptyType deriving (Show, Lift)
+instance WitnessFor EmptyType () where witnessValue = EmptyType
+
+data TupleType ta tb = TupleType ta tb deriving (Show, Lift)
+instance (WitnessFor ta a, WitnessFor tb b) => WitnessFor (TupleType ta tb) (a, b) where witnessValue = TupleType witnessValue witnessValue
+
+data ListType t = ListType t deriving (Show, Lift)
+instance WitnessFor t a => WitnessFor (ListType t) [a] where witnessValue = ListType witnessValue