more intuitive behaviour for 'discardable' in expression bodies

tests/run/tstmtexprs.nim

@@ -0,0 +1,66 @@
+discard """
+  output: '''(bar: bar)
+1244
+6
+abcdefghijklmnopqrstuvwxyz
+145 23'''
+"""
+
+import strutils
+
+when true:
+  proc test(foo: proc (x, y: int): bool) =
+    echo foo(5, 5)
+
+
+  type Foo = object
+    bar: string
+
+  proc newfoo(): Foo =
+    result.bar = "bar"
+
+  echo($newfoo())
+   
+
+  proc retInt(x, y: int): int = 
+    if (var yy = 0; yy != 0):
+      echo yy
+    else:
+      echo(try: parseInt("1244") except EINvalidValue: -1)
+    result = case x
+             of 23: 3
+             of 64: 
+                    case y
+                    of 1: 2
+                    of 2: 3
+                    of 3: 6
+                    else: 8
+             else: 1
+
+  echo retInt(64, 3)
+
+  proc buildString(): string =
+    result = ""
+    for x in 'a'..'z':
+      result.add(x)
+
+  echo buildString()
+
+#test(
+#  proc (x, y: int): bool =
+#  if x == 5: return true
+#  if x == 2: return false
+#  if y == 78: return true
+#)
+
+proc q(): int {.discardable.} = 145
+proc p(): int =
+  q()
+
+proc p2(a: int): int =
+  # result enforces a void context:
+  if a == 2:
+    result = 23
+  q()
+
+echo p(), " ", p2(2)