liboleg-2010.1.7.1: Lambda/CFG2EN.hs

--
-- | <http://okmij.org/ftp/gengo/NASSLLI10>
--
module Lambda.CFG2EN where

-- | Type annotations
--
john, mary :: String
like       :: String
r2         :: String -> String -> String
r1         :: String -> String -> String

john   = "John"
mary   = "Mary"
like   = "likes"
r2 f x = f ++ " " ++ x
r1 x f = x ++ " " ++ f

sentence :: String
sentence = r1 john (r2 like mary)

-- | Unfortunately, the following sentence is, too,
-- accepted by the type checker.
--
-- We shall later see how to build terms that correspond to
-- all and only valid derivations.
-- Invalid derivations will become ill-typed.
bad_sentence :: String
bad_sentence = r2 (r2 like mary) john