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2025-08-20 Original post.

2025-08-24 I'd like to refine the terminology used. The pattern demonstrated here is most accurately described as "polymorphism over effects, (using Higher-Kinded Types)".

It's important to distinguish this from other related concepts. Although it bears a strong resemblance to the Tagless Final pattern, this approach is distinct, and as a tight (not vendor free) integration with Kyo. Furthermore, please note that it is not "Effect Polymorphism," which is an alternate and less precise phrasing.

Thanks a lot to all of you for the valuable feedback!

2025-08-20 Original post.

2025-08-24 I'd like to refine the terminology used. The pattern demonstrated here is most accurately described as "polymorphism over effects, (using Higher-Kinded Types)".

It's important to distinguish this from other related concepts. Although it bears a strong resemblance to the Tagless Final pattern, this approach is distinct, and as a tight (not vendor free) integration with Kyo. Furthermore, please note that it is not "Effect Polymorphism," which is an alternate and less precise phrasing.

Thanks a lot to all of you for the valuable feedback!

I try to write code that is "maximally polymorphic" to the extent that I am sufficiently familiar with the concepts involved and that I am confident of being able to efficiently explain my code to co-workers if needed.

I started to use generics in Java to improve reuse of the libraries I wrote at work, but as I was growing a better understanding of types, parametricity and theorems for free, other compelling reasons became prominent:

the free theorems help me reason about code: given parametricity, I know what a function can do and cannot do, based only on its type signature. Eg. given an unconstrained type variable, any value of this type that appears in positive position (output)

Integers

// `Tuple[Natural, Natural]`
case class Integer(pos: Natural, neg: Natural) { self =>
  def unary_- = copy(neg, pos)
  def + (that: Integer): Integer = Integer(self.pos + that.pos, self.neg + that.neg)
  def - (that: Integer): Integer = this + (-that)
  def * (that: Integer): Integer = Integer(

Aquele erro

Class has been compiled by a more recent version of the Java Environment (class file version 61.0), 
this version of the Java Runtime only recognizes class file versions up to 55.0.

É quando compilamos com Java 17 (class file version 61.0) e tentamos executar com Java 11 (class file version 55.0).

	package baccata

	/**
	* Inspired from Grant Beaty's Scunits
	*/
	trait Bool {
	type branch[B,T <: B, E <: B] <: B // typelevel if-then-else
	type not <: Bool
	type or[R <: Bool] <: Bool
	type and[R <: Bool] <: Bool

	/*
	* Copyright 2020-2021 Typelevel
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software

	package smithy4s.cats

	import cats.Show
	import cats.implicits.toContravariantOps
	import smithy4s.schema.{
	Alt,
	CollectionTag,
	EnumValue,
	Field,
	Primitive,