F＃：类型推断没有找到正确的过载

Question

我写了一个功能，我已经开始重构它，但我有与方法‘圆’一个“独特的过载的一些问题无法确定依据在此节目点之前输入信息。“错误，但我不明白为什么。

let CheckValuesLin (lowValue, highValue) multiplier (sigFigs:int) = 
    let arithmean (lowValue, highValue) = 
     (lowValue + highValue)/2.0 
    let createRangeValue numberModifier meanfunction= 
     let mean = meanfunction (lowValue, highValue) 
     let rangeValue = mean + (numberModifier mean) * multiplier 
     Math.Round(rangeValue, sigFigs) 
    let createRangeValues valueCreatingFunction= 
     (createRangeValue makeNegative arithmean, createRangeValue keepPositive arithmean) 
    let greatestMinValue, lowestMaxValue = createRangeValues createRangeValue 
    (greatestMinValue, lowestMaxValue) 

失败是Math.Round线，当我设置range到range: float其消失的线。这让我感到困惑，因为我徘徊的一切似乎都已经有了正确的类型，包括范围和意思。

我不介意把类型暗示的，我只是想知道为什么会失败。

Answer 1

的问题是，F＃类型推断严格从左到右，从上到下。

在createRangeValue函数中，编译器只能推断出所有的值都是数值型的，没有什么可强制类型为float。

虽然调用arithmean后来似乎给一些值的float类型，调用Round后出现这种情况，所以编译器无法推断类型。

EDIT一些更详细地： 基本上编译器看到这一点：

let lowValue = 0.0 //I am being genrous by making this have a type 
let highValue = 0.0 
let sigFigs = 0 //this type is known 
let createRangeValue (numberModifier) (meanfunction) multiplier= 
    let mean = meanfunction (lowValue, highValue)  
    let rangeValue = mean + (numberModifier mean) * multiplier 
    Math.Round(rangeValue, sigFigs) 

在这种情况下，rangeValue可以是任一float或Decimal既将满足所有约束本。

对于我来说，这工作正常

open System 
let makeNegative a = -a 
let keepPositive a = a 
let CheckValuesLin (lowValue, highValue) multiplier (sigFigs:int) = 
    let arithmean (lowValue, highValue) = 
     (lowValue + highValue)/2.0 
    let createRangeValue numberModifier (meanfunction: float * float -> float)= 
     let mean = meanfunction (lowValue, highValue) 
     let rangeValue = mean + (numberModifier mean) * multiplier 
     Math.Round(rangeValue, sigFigs) 
    let createRangeValues valueCreatingFunction= 
     (createRangeValue makeNegative arithmean, createRangeValue keepPositive arithmean) 
    let greatestMinValue, lowestMaxValue = createRangeValues createRangeValue 
    (greatestMinValue, lowestMaxValue)