F# 函数式编程之 – 习题答案

原文 https://fsharpforfunandprofit.com/posts/computation-expressions-bind/

原文的末尾有一道练习题：

let strToInt str = ???  let stringAddWorkflow x y z =      yourWorkflow          {         let! a = strToInt x         let! b = strToInt y         let! c = strToInt z         return a + b + c         }      // test1 let good = stringAddWorkflow "12" "3" "2" let bad = stringAddWorkflow "12" "xyz" "2"  let strAdd str i = ??? let (>>=) m f = ???  // test2 let good = strToInt "1" >>= strAdd "2" >>= strAdd "3" let bad = strToInt "1" >>= strAdd "xyz" >>= strAdd "3" 

题目要求补充上面代码的未完成部分，使代码正确运行。

做这一道练习题，需要先学习本系列前面的文章以及相关原文。

以下是我的解答：

let strToInt str =     try         Ok (int str)     with     | _ -> Error "not a number"  type MaybeBuilder() =     member this.Bind(x, f) = Result.bind f x     member this.Return(x) = Ok x  let maybe = new MaybeBuilder()  let stringAddWorkflow x y z =      maybe         {         let! a = strToInt x         let! b = strToInt y         let! c = strToInt z         return a + b + c         }      let strAdd str i =     maybe {         let! a = strToInt str         return a + i     }  let (>>=) m f = Result.bind f m  // test let printA x = x |> printfn "%A"  printA <| stringAddWorkflow "12" "3" "2" printA <| stringAddWorkflow "12" "xyz" "2"  strToInt "1" >>= strAdd "2" >>= strAdd "3" |> printA strToInt "1" >>= strAdd "xyz" >>= strAdd "3" |> printA