operations in the abstract syntax

testsuite/compiler/check/abstract-operations/Nat.gf

@@ -0,0 +1,13 @@
+abstract Nat = {
+
+cat Nat ;
+data zero : Nat ;
+     succ : Nat -> Nat ;
+     
+oper plus : Nat -> Nat -> Nat ;
+def  plus zero     y = y ;
+     plus (succ x) y = succ (plus x y) ;
+
+oper twice : Nat -> Nat = \x -> plus x x ;
+
+}