implemented case expressions

tests/reject/tcaseexpr1.nim

@@ -0,0 +1,30 @@
+discard """
+  file: "tcaseexpr1.nim"
+
+  line: 23
+  errormsg: "not all cases are covered"
+
+  line: 29
+  errormsg: "type mismatch: got (string) but expected 'int'"
+"""
+
+type
+  E = enum A, B, C
+
+proc foo(x): auto =
+  return case x
+    of 1..9: "digit"
+    else: "number"
+
+var r = foo(10)
+
+var x = C
+
+var t1 = case x:
+  of A: "a"
+  of B: "b"
+
+var t2 = case x:
+  of A: 10
+  of B, C: "23"
+

tests/run/tcasestm.nim

@@ -1,6 +1,6 @@
 discard """
   file: "tcasestm.nim"
-  output: "ayyy"
+  output: "ayyydd"
 """
 # Test the case statement
 
@@ -22,16 +22,18 @@ of "aa", "bb": write(stdout, "Du bist nicht mein Meister")
 of "cc", "hash", "when": nil
 of "will", "it", "finally", "be", "generated": nil
 
-case i
-of 1..5, 8, 9: nil
-of 6, 7: nil
-elif x == "Ha": 
-  nil
-elif x == "yyy":
-  write(stdout, x)
-else:
-  nil
+var z = case i
+  of 1..5, 8, 9: "aa"
+  of 6, 7: "bb"
+  elif x == "Ha": 
+    "cc"
+  elif x == "yyy":
+    write(stdout, x)
+    "dd"
+  else:
+    "zz"
 
+echo z
 #OUT ayyy