Void context

In a list of statements every expression except the last one needs to have the type void. In addition to this rule an assignment to the builtin result symbol also triggers a mandatory void context for the subsequent expressions:

proc invalid*(): string =
  result = "foo"
  "invalid"  # Error: value of type 'string' has to be discarded

proc valid*(): string =
  let x = 317
  "valid"