拥抱不要让脚本文件使用关键字"让"

Question

我将此文件作为模块加载到Hugs,但是出现此错误:

错误文件:.\ Hugs.hs:38 - 输入中的语法错误(意外关键字"let")

data MetricUnit = Meter
            | Liter
            | KiloGram
              deriving (Show, Eq)

data ImperialUnit = Yard
              | Gallon
              | Pound
                deriving (Show, Eq)

data Measurement = MetricMeasurement Double MetricUnit
             | ImperialMeasurement Double ImperialUnit
               deriving (Show)

symbol :: MetricUnit -> String
symbol x
  | x == Meter = "m"
  | x == Liter = "L"
  | x == KiloGram = "kg"

convert (MetricMeasurement x u)
  | u==Meter    = ImperialMeasurement (1.0936*x) Yard
  | u==Liter    = ImperialMeasurement (0.2642*x) Gallon
  | u==KiloGram = ImperialMeasurement (2.2046*x) Pound

convert (ImperialMeasurement x u)
  | u==Yard   = MetricMeasurement (0.9144*x) Meter
  | u==Gallon = MetricMeasurement (3.7854*x) Liter
  | u==Pound  = MetricMeasurement (0.4536*x) KiloGram

let fac n = if n == 0 then 1 else n * fac (n-1)   --This line doesn't work
let m = MetricMeasurement 2 Meter

Answer 1

你不能let在顶层发表声明.简单写一下

fac n = if n == 0 then 1 else n * fac (n-1)
m = MetricMeasurement 2 Meter