added test cases for computation with abstract syntax terms

testsuite/runtime/eval/Test.gf

@@ -0,0 +1,28 @@
+abstract Test = {
+
+fun f : Int -> Int -> Int ;
+
+fun g : Int -> Int ;
+def g 1 = 2 ;
+
+fun g2 : Int -> Int -> Int ;
+def g2 1 x = x ;
+
+fun g0 : Int -> Int -> Int ;
+def g0 = g2 ;
+
+fun const : Int -> Int -> Int ;
+def const x _ = x ;
+
+cat Nat ;
+
+data zero : Nat ;
+     succ : Nat -> Nat ;
+     err  : Nat ;
+
+fun dec : Nat -> Nat ;
+def dec zero     = zero ;
+    dec (succ n) = n ;
+    dec n        = err ; -- for fall through checking
+
+}