This expression was expected to have type string,but here has type Gen<string>

Question

I have this record:

type Client = 
   { Name : string; Income : int ; YearsInJob : int
     UsesCreditCard : bool;  CriminalRecord : bool }

To create a generator for this record, I have tried the follwing code:

let chooseFromList xs =
    gen {
        let! idx = Gen.choose(0, List.length xs - 1)
        return (List.nth xs idx)
    }



let generateName = (Gen.oneof [ gen {return "A"};gen {return "B"};gen {return "C"}])
let generateIncome=  (chooseFromList [0..5000])
let generate_YearsInJob= chooseFromList [0..45]
let generate_UsesCreditCard = (Gen.oneof [ gen { return true }; gen { return false } ])
let generate_UsesCriminalRecord= (Gen.oneof [ gen { return true }; gen { return false } ])



let genertate_Client =
{

      Name= generateName;
      Income=generateIncome;
      YearsInJob=generate_YearsInJob
      UsesCreditCard=generate_UsesCreditCard
      CriminalRecord=generate_UsesCriminalRecord
}

The problem is in line Name= generateName; i am encounter with the erorr:

This expression was expected to have type string,but here has type Gen<string>

and this error exists for last remaining line.

Fix the type of Name? Or ask it for the first value? Or build a string out of everything? Or maybe OneOf the strings (and not generators, each which yields a different string)? The error is what it says: a gen'erator is not a string. — user2864740

Random Dev Random Dev · Accepted Answer · 2015-11-25T05:21:10

As you want an generator for your Clients you have to generate examples for your fields-data first - so the gen { ... } syntax comes in handy:

let genertate_Client =
   gen {
      let! name = generateName
      let! income = generateIncome
      let! yearsInJob = generate_YearsInJob
      let! creditCard = genergenerate_UsesCreditCard
      let! criminal = generate_UsesCriminalRecord
      return { 
         Name = name; 
         Income = income;
         YearsInJob = yearsInJob;
         UsesCreditCard = creditCard;
         CriminalRecord = criminal }
   }

here of course you generate examples out of generators using the let! syntax inside the computation

This expression was expected to have type string,but here has type Gen<string>

1 Answers