command syntax is allowed in expressions

tests/parser/tcommand_as_expr.nim

@@ -0,0 +1,12 @@
+discard """
+  output: "12"
+"""
+
+proc foo(x: int): int = x-1
+proc foo(x, y: int): int = x-y
+
+let x = foo 7.foo,  # comment here
+            foo(1, foo 8)
+#  12 =       6     -     -6
+echo x
+