add the barest skeleton of a library

src/MyLib.hs

-module MyLib (someFunc) where
-
-someFunc :: IO ()
-someFunc = putStrLn "someFunc"

src/Tahoe/Capability.hs

+module Tahoe.Capability where

tahoe-capabilities.cabal

@@ -64,7 +64,7 @@ library
   import:           warnings
 
   -- Modules exported by the library.
-  exposed-modules:  MyLib
+  exposed-modules:  Tahoe.Capability
 
   -- Modules included in this library but not exported.
   -- other-modules: