别名解析器功能

Question

为方便起见，许多关于Parsec别名函数名的Haskell教程。别名在这里可能是错误的技术词，但想法是为函数使用更简单或替代的名称。

使用ghci 8.0.1，以下内容给出错误：

digits = ['one', 'two',   'three', 'four', 'five', 
          'six', 'seven', 'eight', 'nine']

teens  = ['ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 
          'sixteen', 'seventeen', 'eighteen', 'nineteen']

tens   = ['twenty', 'thirty', 'fourty', 'fifty', 
          'sixty', 'seventy', 'eighty', 'ninety']

for word in digits + teens:
    print(word)

for tens_word in tens:
    print(tens_word)        # e.g. twenty

    for digits_word in digits:
        print(tens_word, digits_word)   # e.g. twenty one

print("one hundred")

这是错误：

import Text.ParserCombinators.Parser
run = parseTest

我做错了什么，因为说出以下内容是正确的？

error:
    • Ambiguous type variable ‘a0’ arising from a use of ‘parseTest’
      prevents the constraint ‘(Show a0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘a0’ should be.
      These potential instances exist:
        instance Show Ordering -- Defined in ‘GHC.Show’
        instance Show Integer -- Defined in ‘GHC.Show’
        instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
        ...plus 22 others
        ...plus 17 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • When instantiating ‘run’, initially inferred to have
      this overly-general type:
        forall s t a.
        (Text.Parsec.Prim.Stream s Data.Functor.Identity.Identity t,
         Show a) =>
        Text.Parsec.Prim.Parsec s () a -> s -> IO ()
      NB: This instantiation can be caused by the monomorphism restriction.
Failed, modules loaded: none.