您可以定义类似

data Symbolic n
   = Constant n
   | Variable String
   | Symbolic n :+ Symbolic n
   | Symbolic n :* Symbolic n
  deriving (Show)

GHCi>令v =变量； c =常量
GHCi> c 2:* v"a":+ c 3
(常数2:*变量"a"):+常数3

GHCi> let v = Variable; c = Constant
GHCi> c 2 :* v"a" :+ c 3
    (Constant 2 :* Variable "a") :+ Constant 3

第一句话就是这个意思.

That's what the first phrase refers to.