Scala minimum imports required for right and left injection

Question

A simple question, I already looked at this: Import control in Scalaz7 , but I can’t figure out how to minimally introduce right and left into my objects to create instances \/ .

I tried:

import syntax.ToDataOps and other To... options, such as syntax.ToIdOps , as suggested at http://eed3si9n.com/learning-scalaz-day13 .

A simple example:

 import scalaz.{\/, syntax} import // What goes here class Test { def returnEitherT(h: Int): String \/ Int = { h right } } 

Thanks, Jason.

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I solved this using import syntax.id._ , but I'm not sure why this worked.

Answer 1

syntax.id contains the syntax for "simple" values, i.e. It does not contain restrictions on the type of value.

In general, when you import the syntax of an x.op form x.op , the place to import the syntax depends on type x , because op must be a valid operation for that type.

Since \/[A, B] universally quantized for A and B, using the syntax x.left and x.right does not bind constraints of type x . Therefore, it belongs to syntax.id .

To understand what syntax is available there, it is worth looking at the source of some of the modules that make up syntax packages. For example, contrast IdOps[A] , which has syntax for any A , with FunctorOps[F[_],A] , which has the requirement that F be a Functor .

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I don’t know where exactly the name id comes from; perhaps this is due to the identity functor id , which can be defined as type Id[A] = A If you needed to choose a type restriction for values ​​that can be used with syntax.id , this means that they are in id . Being universally quantified in A , operations cannot know about the structure of the value of A , therefore they cannot be operations of changing the structure to A

Answer 2

Since scalaz 7 is the correct import:

 import scalaz.syntax.either._