app/Gyehoek/Syntax.hs

@@ -11,6 +11,7 @@ import Language.SexpGrammar.Generic
 import GHC.Generics
 import Prelude hiding ((.), id)
 import Control.Category
+import Data.List.NonEmpty (NonEmpty ((:|)))
 
 
 type Name = Text
@@ -27,7 +28,7 @@ data Val
   deriving (Show, Generic)
 
 data Exp
-  = ExpLet (List (Name, Exp)) Exp
+  = ExpLet (NonEmpty (Name, Exp)) Exp
   | ExpApply Exp (List Exp)
   | ExpBegin (List Exp)
   | ExpVal Val
@@ -35,15 +36,20 @@ data Exp
 
 
 
+nonempty :: SexpGrammar a -> SexpGrammar (NonEmpty a)
+nonempty a =
+  list (el a >>> rest a) >>>
+    pair >>> iso (uncurry (:|)) (\(x :| xs) -> (x, xs))
+
 letIso
   :: (forall t. Grammar Position (Sexp :- t) (a :- t))
   -> (forall t. Grammar Position (Sexp :- t) (b :- t))
-  -> Grammar Position (Sexp :- (List (a, b) :- t1)) t2
+  -> Grammar Position (Sexp :- (NonEmpty (a, b) :- t1)) t2
   -> Grammar Position (Sexp :- t1) t2
 letIso name rhs e = list (el (sym "let") >>> el bindings >>> el e)
   where
     -- bindings :: Grammar Position (Sexp :- _) (List (_, _) :- _)
-    bindings = list $ rest binding
+    bindings = nonempty binding
     binding :: Grammar Position (Sexp :- t) ((_, _) :- t)
     binding = list (el name >>> el rhs) >>> pair