Created
September 15, 2011 17:57
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My Scalaz error
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import scalaz._ | |
import Scalaz._ | |
scala> val a = (_:List[Int]).partition(_ > 5) | |
a: List[Int] => (List[Int], List[Int]) = <function1> | |
scala> val b = (_:List[Int]).partition(_ > 10) | |
b: List[Int] => (List[Int], List[Int]) = <function1> | |
scala> val c = (_:List[Int]).map(_ + 1) | |
c: List[Int] => List[Int] = <function1> | |
scala> a andThen b.first andThen c.first.first apply List(1,2,3,20,30,40,50,100,200,300) | |
res0: ((List[Int], List[Int]), List[Int]) = ((List(21, 31, 41, 51, 101, 201, 301),List()),List(1, 2, 3)) | |
scala> a andThen b.first andThen c.first.second apply List(1,2,3,20,30,40,50,100,200,300) | |
<console>:17: error: polymorphic expression cannot be instantiated to expected type; | |
found : [C(in method first), C(in method second)](C(in method second), (List[Int], C(in method first))) => (C(in method second), (List[Int], C(in method first))) | |
required: ((List[Int], List[Int]), List[Int]) => ? | |
a andThen b.first andThen c.first.second apply List(1,2,3,20,30,40,50,100,200,300) | |
scala> a andThen b.second andThen c.second.second apply List(1,2,3,20,30,40,50,100,200,300) | |
res5: (List[Int], (List[Int], List[Int])) = (List(20, 30, 40, 50, 100, 200, 300),(List(),List(2, 3, 4))) | |
scala> a andThen b.second andThen c.second.first apply List(1,2,3,20,30,40,50,100,200,300) | |
<console>:17: error: polymorphic expression cannot be instantiated to expected type; | |
found : [C(in method second), C(in method first)]((C(in method second), List[Int]), C(in method first)) => ((C(in method second), List[Int]), C(in method first)) | |
required: (List[Int], (List[Int], List[Int])) => ? | |
a andThen b.second andThen c.second.first apply List(1,2,3,20,30,40,50,100,200,300) |
In case of c.first.first
composition succeeds because types match.
scala> c.first.first
res113: (((List[Int], Nothing), Nothing)) => ((List[Int], Nothing), Nothing) = <function1>
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Types are incompatible. So the composition fails.