- tr ∷ (MIMEType, [Text]) → [ (Text, MIMEType) ]
- tr (mime, exts) = [ (ext, mime) | ext ← exts ]
+ tr ∷ (v, [k]) → [(k, v)]
+ tr (v, ks) = [(k, v) | k ← ks]
+
+ go ∷ Ord k ⇒ Map k v → [(k, v)] → Either (k, v, v) (Map k v)
+ go m [] = Right m
+ go m ((k, v):xs)
+ = case M.insertLookupWithKey' f k v m of
+ (Nothing, m') → go m' xs
+ (Just v0, _ ) → Left (k, v0, v)
+
+ f ∷ k → v → v → v
+ f _ _ = id