added test cases for computation with abstract syntax terms

testsuite/runtime/eval/eval.gfs.gold

@@ -0,0 +1,50 @@
+\v0 -> v0 1␍
+␍
+? 1␍
+␍
+? 1␍
+␍
+unknown variable unknown_var␍
+unknown variable unknown_var␍
+literal of function type␍
+f 1 2␍
+␍
+\v0 -> v0␍
+␍
+?666␍
+␍
+f␍
+␍
+f 1 2␍
+␍
+literal of function type␍
+2␍
+␍
+g 0␍
+␍
+\v0 -> g v0␍
+␍
+g ?␍
+␍
+5␍
+␍
+3␍
+␍
+g2␍
+␍
+f 3.2␍
+␍
+g2 2.3␍
+␍
+g2 (f 0) 1␍
+␍
+3.14␍
+␍
+succ zero␍
+␍
+?␍
+␍
+\v0 -> dec v0␍
+␍
+dec ?␍
+␍