Adjust case of first letter for namespace (#189)

hs-bindgen/src/HsBindgen/Hs/AST/Name.hs

@@ -6,8 +6,10 @@ module HsBindgen.Hs.AST.Name (
   , toHsName
   ) where
 
+import Data.Char qualified as Char
 import Data.String
 import Data.Text (Text)
+import Data.Text qualified as T
 
 import HsBindgen.C.AST (CName(..))
 
@@ -39,9 +41,38 @@ newtype HsName (ns :: Namespace) = HsName { getHsName :: Text }
 class ToHsName (ns :: Namespace) where
   toHsName :: CName -> HsName ns
 
--- | (Wrong) catch-all instance
+-- TODO <https://github.com/well-typed/hs-bindgen/issues/189>
 --
--- TODO: <https://github.com/well-typed/hs-bindgen/issues/189>
--- We need to properly implement this.
-instance ToHsName ns where
-  toHsName = HsName . getCName
+-- The following instances just adjust the case of the first letter of the name
+-- as required, according to the target namespace.  We will add a context and
+-- options as well as consider edge cases in future commits.
+
+instance ToHsName NsVar where
+  toHsName = toHsName' Char.toLower
+
+instance ToHsName NsConstr where
+  toHsName = toHsName' Char.toUpper
+
+instance ToHsName NsTypeVar where
+  toHsName = toHsName' Char.toLower
+
+instance ToHsName NsTypeConstr where
+  toHsName = toHsName' Char.toUpper
+
+instance ToHsName NsTypeClass where
+  toHsName = toHsName' Char.toUpper
+
+instance ToHsName NsModuleName where
+  toHsName = toHsName' Char.toUpper
+
+toHsName' ::
+     (Char -> Char)  -- ^ case conversion for first character
+  -> CName
+  -> HsName ns
+toHsName' f = HsName . aux . getCName
+  where
+    aux :: Text -> Text
+    aux t = case T.uncons t of
+      Just (c, t')
+        | Char.isLetter c -> T.cons (f c) t'
+      _otherwise -> t