daml - 如何按 DAML 中的一些自定义条件对列表进行排序？

Question

假设我有一个名为 Mortgage 的自定义类型列表，定义如下：

data Mortgage = Mortgage {
  rate: Decimal; 
  issuedDate: Datetime;
  amount: Decimal
} deriving (Eq, Show)

在这种特殊的一次性情况下，我想根据issuedDate 对列表进行降序排序。我怎样才能做到这一点？

Answer 1

DA.List在标准库的模块中，您将找到功能sortBy以及sortOn哪些功能可以满足您的需求。

具体来说，使用sortOn：

sortMortgages: [Mortgage] -> [Mortgage] = reverse . sortOn (\m -> m.issuedDate)

一个完整的例子：

daml 1.2
module Main where

import DA.Date
import DA.List

data Mortgage = Mortgage {
  rate: Decimal;
  issuedDate: Time;
  amount: Decimal
} deriving (Eq, Show)

sortMortgages: [Mortgage] -> [Mortgage] = reverse . sortOn (\m -> m.issuedDate)

testSortMortgages = scenario
  let
    mort1 = Mortgage with rate = 0.3; issuedDate = datetime 2007 Apr 5 14 30 05 ; amount = 1.0
    mort2 = Mortgage with rate = 0.2; issuedDate = datetime 2007 Apr 5 14 30 15 ; amount = 2.0
    mort3 = Mortgage with rate = 0.1; issuedDate = datetime 2007 Apr 5 14 30 10 ; amount = 3.0
    mortgages = [ mort1, mort2, mort3 ]
    expected = [ mort2, mort3, mort1 ]
  in
    assert $ sortMortgages mortgages == expected