Haskell 产生如此多错误报告的简单代码

我正试着做上述的MannWhitney-U测试。以下是我的代码：

import Data.Vector as V
import Data.Vector.Unboxed as VU
import Statistics.Test.MannWhitneyU

sampleA = [1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4]
sampleB = [2.0, 4.0, 5.0, 5.0, 3.0, 4.0, 5.0, 6]

main = do 
    putStrLn "\nResult of mannWhitneyUtest: "
    print (mannWhitneyUtest SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB) )

但是，错误比上述代码长得多：

[1 of 1] Compiling Main             ( rnmann.hs, rnmann.o )

rnmann.hs:6:12: error:
    • Ambiguous type variable ‘t0’ arising from the literal ‘1.0’
      prevents the constraint ‘(Fractional t0)’ from being solved.
      Relevant bindings include sampleA :: [t0] (bound at rnmann.hs:6:1)
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      These potential instances exist:
        instance Fractional Double -- Defined in ‘GHC.Float’
        instance Fractional Float -- Defined in ‘GHC.Float’
        ...plus four instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: 1.0
      In the expression: [1.0, 2.0, 3.0, 4.0, ....]
      In an equation for ‘sampleA’: sampleA = [1.0, 2.0, 3.0, ....]

rnmann.hs:6:47: error:
    • Ambiguous type variable ‘t0’ arising from the literal ‘4’
      prevents the constraint ‘(Num t0)’ from being solved.
      Relevant bindings include sampleA :: [t0] (bound at rnmann.hs:6:1)
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      These potential instances exist:
        instance Num Integer -- Defined in ‘GHC.Num’
        instance Num Double -- Defined in ‘GHC.Float’
        instance Num Float -- Defined in ‘GHC.Float’
        ...plus two others
        ...plus 13 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: 4
      In the expression: [1.0, 2.0, 3.0, 4.0, ....]
      In an equation for ‘sampleA’: sampleA = [1.0, 2.0, 3.0, ....]

rnmann.hs:7:12: error:
    • Ambiguous type variable ‘t0’ arising from the literal ‘2.0’
      prevents the constraint ‘(Fractional t0)’ from being solved.
      Relevant bindings include sampleB :: [t0] (bound at rnmann.hs:7:1)
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      These potential instances exist:
        instance Fractional Double -- Defined in ‘GHC.Float’
        instance Fractional Float -- Defined in ‘GHC.Float’
        ...plus four instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: 2.0
      In the expression: [2.0, 4.0, 5.0, 5.0, ....]
      In an equation for ‘sampleB’: sampleB = [2.0, 4.0, 5.0, ....]

rnmann.hs:7:47: error:
    • Ambiguous type variable ‘t0’ arising from the literal ‘6’
      prevents the constraint ‘(Num t0)’ from being solved.
      Relevant bindings include sampleB :: [t0] (bound at rnmann.hs:7:1)
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      These potential instances exist:
        instance Num Integer -- Defined in ‘GHC.Num’
        instance Num Double -- Defined in ‘GHC.Float’
        instance Num Float -- Defined in ‘GHC.Float’
        ...plus two others
        ...plus 13 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: 6
      In the expression: [2.0, 4.0, 5.0, 5.0, ....]
      In an equation for ‘sampleB’: sampleB = [2.0, 4.0, 5.0, ....]

rnmann.hs:11:16: error:
    • Ambiguous type variable ‘t0’ arising from a use of ‘mannWhitneyUtest’
      prevents the constraint ‘(Ord t0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      These potential instances exist:
        instance Ord Ordering -- Defined in ‘GHC.Classes’
        instance Ord Integer
          -- Defined in ‘integer-gmp-1.0.0.1:GHC.Integer.Type’
        instance Ord PositionTest -- Defined in ‘Statistics.Test.Types’
        ...plus 26 others
        ...plus 25 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the first argument of ‘print’, namely
        ‘(mannWhitneyUtest
            SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB))’
      In a stmt of a 'do' block:
        print
          (mannWhitneyUtest
             SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB))
      In the expression:
        do { putStrLn
               "\n\
               \Result of mannWhitneyUtest: ";
             print
               (mannWhitneyUtest
                  SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB)) }

rnmann.hs:11:47: error:
    • No instance for (Fractional (Statistics.Types.PValue Double))
        arising from the literal ‘0.05’
    • In the second argument of ‘mannWhitneyUtest’, namely ‘0.05’
      In the first argument of ‘print’, namely
        ‘(mannWhitneyUtest
            SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB))’
      In a stmt of a 'do' block:
        print
          (mannWhitneyUtest
             SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB))

rnmann.hs:11:75: error:
    • Ambiguous type variable ‘t0’ arising from a use of ‘VU.fromList’
      prevents the constraint ‘(Unbox t0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘t0’ should be.
      These potential instances exist:
        instance Unbox () -- Defined in ‘Data.Vector.Unboxed.Base’
        instance (Unbox a, Unbox b) => Unbox (a, b)
          -- Defined in ‘Data.Vector.Unboxed.Base’
        instance (Unbox a, Unbox b, Unbox c) => Unbox (a, b, c)
          -- Defined in ‘Data.Vector.Unboxed.Base’
        ...plus 9 others
        ...plus 16 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the fourth argument of ‘mannWhitneyUtest’, namely
        ‘(VU.fromList sampleB)’
      In the first argument of ‘print’, namely
        ‘(mannWhitneyUtest
            SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB))’
      In a stmt of a 'do' block:
        print
          (mannWhitneyUtest
             SamplesDiffer 0.05 (VU.fromList sampleA) (VU.fromList sampleB))

我认为关键问题是如何将0.05作为Pvalue

---

感谢您的帮助。

以下是错误报告中与此超级相关的部分

由文本“4”产生的不明确类型变量“t0”

可能的修复：使用类型注释指定“t0”应该是什么

它是一个

Int

，

Double

，

Float

？编译器无法分辨，因为它是不明确的

添加类型签名应该可以解决问题

sampleA :: [Double]

---

您不能使用

0.05

，因为您可以使用来构造

PValue

：

import Statistics.Types(mkPValue)

main = do 
    putStrLn "\nResult of mannWhitneyUtest: "
    print $
       mannWhitneyUtest SamplesDiffer (mkPValue 0.05) (VU.fromList sampleA) (VU.fromList sampleB)

---

这不是输出，这些是编译错误。是的，我指的是错误报告。在

samreak

上的显式类型签名可以帮助您找到此错误。根据经验：当类型错误消息令人困惑时，添加更多类型签名。它通常不会解决问题，但会改善错误消息。在我之前的示例中，我从未需要这样做。

Result of mannWhitneyUtest: 
Just Significant