表达式为“A._”的Haskell令牌

Question

Haskell如何解释表达式A._？ 例如。在main = print $ A._。

Haskell抛出以下错误错误：

source_file.hs:1:16:
    Found hole ‘_’ with type: r0
    Where: ‘r0’ is an ambiguous type variable
    Relevant bindings include
      main :: IO ()
        (bound at source_file.hs:1:1)
    In the second argument of ‘($)’, namely ‘A._’
    In the expression: print $ A._
    In an equation for ‘main’: main = print $ A._

但是，根据Haskell的Syntax Reference，A._应该被解释为consym (A)，varsym (.)和reservedid (_)，因为_不是有效varid（varid s不能为reservedid s。。

Haskell为main = print $ A._t抛出相同的错误：

source_file.hs:1:16:
    Found hole ‘_t’ with type: r0
    Where: ‘r0’ is an ambiguous type variable
    Relevant bindings include
      main :: IO ()
        (bound at source_file.hs:1:1)
    In the second argument of ‘($)’, namely ‘A._t’
    In the expression: print $ A._t
    In an equation for ‘main’: main = print $ A._t

但是，在这种情况下，令牌序列应为qvarid (A._t)，A匹配modid，_t匹配varid。

有人可以帮我解释发生了什么事吗？