How to find an element in an array of records in Purescript

Question

everyone. I'd like to find an element in an array of records in Purescript but since I'm not familiar with Purescripot, I can't solve it.

I have an array banks which contains bank records.

This is the type of bank record.

type Bank = {
  id :: Int,
  name :: String
}

I want to get a bank in banks whose id is the same as a given search id.

I tried as following:

find (_.id == searchId) banks

but getting this error.


Could not match type
    Int
  with type
    Function
      { id :: t0
      | t1
      }

Please help me with this simple issue.

Fyodor Soikin · Accepted Answer · 2019-12-15 16:08:23Z

5

The expression _.id is a function that takes a Bank and returns its id (a bit oversimplifying, but good enough for now).

To illustrate:

getId = _.id
bank = { id: 42, name: "my bank" }
getId bank == 42

And then you take that function and try to compare it with searchId, which I'm assuming is a number.

Well, you can't compare functions with numbers, and that's what the compiler is telling you: "Could not match type Int with type Function"

The function find expects to get as its first argument a function that takes a Bank and returns a Boolean. There are many ways to produce such a function, but the most obvious one would be with a lambda abstraction:

\bank -> bank.id == searchId

So to plug it into your code:

find (\bank -> bank.id == searchId) banks

answered Dec 15, 2019 at 16:08

Fyodor Soikin

81.3k10 gold badges134 silver badges179 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

goldvenus · Accepted Answer · 2019-12-15 18:23:05Z

1

You can change your code like this.

find(\{id} -> id == searchId) banks

So you can get the result object.

answered Dec 15, 2019 at 18:23

goldvenus

9382 gold badges11 silver badges22 bronze badges

Collectives™ on Stack Overflow

How to find an element in an array of records in Purescript

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related