app/Gyehoek/Sexp.hs

@@ -10,6 +10,8 @@ module Gyehoek.Sexp
   , encode
   , decode
   , parseSexps
+  , prefixSugar
+  , todo
   )
 where
 
@@ -33,6 +35,7 @@ import GHC.IO.Unsafe (unsafePerformIO)
 import qualified Data.Text.IO as TIO
 import Control.Monad (join)
 import qualified Language.Sexp.Located as SexpLoc
+import Data.Void (absurd)
 
 
 sexp :: SexpIso a => Iso' a Text
@@ -80,6 +83,24 @@ dotlist x = list $ rest $ coproduct
   [ x >>> _
   ]
 
+-- | Define a sexp representation as either (⟨name⟩ ⟨e⟩) or '⟨e⟩.
+prefixSugar
+  :: Text -> Prefix
+  -> Grammar Position (Sexp :- t') a
+  -> Grammar Position (Sexp :- t') a
+prefixSugar name prefix e = coproduct
+  -- 'something
+  [ Sexp.prefixed prefix e
+  -- (quote something)
+  , list $ el (sym name) >>> el e
+  ]
+
+todo :: Grammar p (Sexp :- t) t'
+todo = (IGB.Flip $ IGB.PartialIso absurd f) >>> IGB.PartialIso absurd g
+  where
+    f _ = Left $ unexpected "todo"
+    g _ = Left $ unexpected "todo"
+
 lambda
   :: (forall t. Grammar Position (Sexp :- t) (a :- t))
   -> Grammar Position (Sexp :- List a :- t1) t2