How to stop execution in for-comprehension if Option is None using cats IO?
up vote
6
down vote
favorite
1
If i just use Option in for-comprehension everything goes as expected:
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
aa <- a
bb <- b
cc <- c
} yield aa + bb + cc
println(r) // None, because b is None
but how to achieve the same behaviour using cats IO?
import cats.effect.IO
// in reality this will be a methods with side effect
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- IO{println("a"); a}
_ <- IO{println("b"); b} // want to stop execution here
_ <- IO{println("c"); c}
} yield ()
r.unsafeRunSync()
In result i get a b c, but i expect only a b.
Is it possible to achieve? Is it a right way to do it?
scala functional-programming monads scala-cats
edited Nov 20 at 13:51
erip
10.1k43674
asked Nov 20 at 12:54
Nick Ryan
362213
add a comment |
up vote
6
down vote
favorite
1
If i just use Option in for-comprehension everything goes as expected:
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
aa <- a
bb <- b
cc <- c
} yield aa + bb + cc
println(r) // None, because b is None
but how to achieve the same behaviour using cats IO?
import cats.effect.IO
// in reality this will be a methods with side effect
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- IO{println("a"); a}
_ <- IO{println("b"); b} // want to stop execution here
_ <- IO{println("c"); c}
} yield ()
r.unsafeRunSync()
In result i get a b c, but i expect only a b.
Is it possible to achieve? Is it a right way to do it?
scala functional-programming monads scala-cats
edited Nov 20 at 13:51
erip
10.1k43674
asked Nov 20 at 12:54
Nick Ryan
362213
add a comment |
up vote
6
down vote
favorite
1
up vote
6
down vote
favorite
1
1
If i just use Option in for-comprehension everything goes as expected:
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
aa <- a
bb <- b
cc <- c
} yield aa + bb + cc
println(r) // None, because b is None
but how to achieve the same behaviour using cats IO?
import cats.effect.IO
// in reality this will be a methods with side effect
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- IO{println("a"); a}
_ <- IO{println("b"); b} // want to stop execution here
_ <- IO{println("c"); c}
} yield ()
r.unsafeRunSync()
In result i get a b c, but i expect only a b.
Is it possible to achieve? Is it a right way to do it?
scala functional-programming monads scala-cats
edited Nov 20 at 13:51
erip
10.1k43674
asked Nov 20 at 12:54
Nick Ryan
362213
If i just use Option in for-comprehension everything goes as expected:
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
aa <- a
bb <- b
cc <- c
} yield aa + bb + cc
println(r) // None, because b is None
but how to achieve the same behaviour using cats IO?
import cats.effect.IO
// in reality this will be a methods with side effect
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- IO{println("a"); a}
_ <- IO{println("b"); b} // want to stop execution here
_ <- IO{println("c"); c}
} yield ()
r.unsafeRunSync()
In result i get a b c, but i expect only a b.
Is it possible to achieve? Is it a right way to do it?
scala functional-programming monads scala-cats
scala functional-programming monads scala-cats
edited Nov 20 at 13:51
erip
10.1k43674
asked Nov 20 at 12:54
Nick Ryan
362213
edited Nov 20 at 13:51
erip
10.1k43674
asked Nov 20 at 12:54
Nick Ryan
362213
edited Nov 20 at 13:51
erip
10.1k43674
edited Nov 20 at 13:51
erip
10.1k43674
edited Nov 20 at 13:51
erip
10.1k43674
10.1k43674
asked Nov 20 at 12:54
Nick Ryan
362213
asked Nov 20 at 12:54
Nick Ryan
362213
asked Nov 20 at 12:54
Nick Ryan
362213
362213
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
up vote
7
down vote
accepted
You can do this with monad transformers; specifically, you'll want to use OptionT[IO, T] here:
import cats.effect._
import cats.data.OptionT
import cats.implicits._
import cats.effect.IO
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- OptionT[IO, Int](IO {println("a"); a})
_ <- OptionT[IO, Int](IO {println("b"); b})
_ <- OptionT[IO, Int](IO {println("c"); c})
} yield ()
r.value.unsafeRunSync()
See it in action here.
answered Nov 20 at 13:33
erip
10.1k43674
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
7
down vote
accepted
You can do this with monad transformers; specifically, you'll want to use OptionT[IO, T] here:
import cats.effect._
import cats.data.OptionT
import cats.implicits._
import cats.effect.IO
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- OptionT[IO, Int](IO {println("a"); a})
_ <- OptionT[IO, Int](IO {println("b"); b})
_ <- OptionT[IO, Int](IO {println("c"); c})
} yield ()
r.value.unsafeRunSync()
See it in action here.
answered Nov 20 at 13:33
erip
10.1k43674
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
add a comment |
up vote
7
down vote
accepted
You can do this with monad transformers; specifically, you'll want to use OptionT[IO, T] here:
import cats.effect._
import cats.data.OptionT
import cats.implicits._
import cats.effect.IO
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- OptionT[IO, Int](IO {println("a"); a})
_ <- OptionT[IO, Int](IO {println("b"); b})
_ <- OptionT[IO, Int](IO {println("c"); c})
} yield ()
r.value.unsafeRunSync()
See it in action here.
answered Nov 20 at 13:33
erip
10.1k43674
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
add a comment |
up vote
7
down vote
accepted
up vote
7
down vote
accepted
You can do this with monad transformers; specifically, you'll want to use OptionT[IO, T] here:
import cats.effect._
import cats.data.OptionT
import cats.implicits._
import cats.effect.IO
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- OptionT[IO, Int](IO {println("a"); a})
_ <- OptionT[IO, Int](IO {println("b"); b})
_ <- OptionT[IO, Int](IO {println("c"); c})
} yield ()
r.value.unsafeRunSync()
See it in action here.
answered Nov 20 at 13:33
erip
10.1k43674
You can do this with monad transformers; specifically, you'll want to use OptionT[IO, T] here:
import cats.effect._
import cats.data.OptionT
import cats.implicits._
import cats.effect.IO
val a = Some(1)
val b = None
val c = Some(3)
val r = for {
_ <- OptionT[IO, Int](IO {println("a"); a})
_ <- OptionT[IO, Int](IO {println("b"); b})
_ <- OptionT[IO, Int](IO {println("c"); c})
} yield ()
r.value.unsafeRunSync()
See it in action here.
answered Nov 20 at 13:33
erip
10.1k43674
edited Nov 20 at 13:38
answered Nov 20 at 13:33
erip
10.1k43674
answered Nov 20 at 13:33
erip
10.1k43674
answered Nov 20 at 13:33
erip
10.1k43674
10.1k43674
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
add a comment |
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
Thank you! It's exactly what i need!
– Nick Ryan
Nov 20 at 13:37
add a comment |
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