refined: simple refinement types for Scala

refined is a Scala library for refining types with type-level predicates which constrain the set of values described by the refined type. It started as a port of the refined Haskell library (which also provides an excellent motivation why this kind of library is useful).

A quick example:

import eu.timepit.refined._
import eu.timepit.refined.api.Refined
import eu.timepit.refined.auto._
import eu.timepit.refined.numeric._

// This refines Int with the Positive predicate and checks via an
// implicit macro that the assigned value satisfies it:
scala> val i1: Int Refined Positive = 5
i1: Int Refined Positive = 5

// If the value does not satisfy the predicate, we get a meaningful
// compile error:
scala> val i2: Int Refined Positive = -5
<console>:22: error: Predicate failed: (-5 > 0).
       val i2: Int Refined Positive = -5
                                       ^

// There is also the explicit refineMV macro that can infer the base
// type from its parameter:
scala> refineMV[Positive](5)
res0: Int Refined Positive = 5

// Macros can only validate literals because their values are known at
// compile-time. To validate arbitrary (runtime) values we can use the
// refineV function:

scala> val x = 42 // suppose the value of x is not known at compile-time

scala> refineV[Positive](x)
res1: Either[String, Int Refined Positive] = Right(42)

scala> refineV[Positive](-x)
res2: Either[String, Int Refined Positive] = Left(Predicate failed: (-42 > 0).)

refined also contains inference rules for converting between different refined types. For example, Int Refined Greater[W.`10`.T] can be safely converted to Int Refined Positive because all integers greater than ten are also positive. The type conversion of refined types is a compile-time operation that is provided by the library:

scala> val a: Int Refined Greater[W.`5`.T] = 10
a: Int Refined Greater[Int(5)] = 10

// Since every value greater than 5 is also greater than 4, `a` can be
// ascribed the type Int Refined Greater[W.`4`.T]:
scala> val b: Int Refined Greater[W.`4`.T] = a
b: Int Refined Greater[Int(4)] = 10

// An unsound ascription leads to a compile error:
scala> val c: Int Refined Greater[W.`6`.T] = a
<console>:23: error: type mismatch (invalid inference):
 Greater[Int(5)] does not imply
 Greater[Int(6)]
       val c: Int Refined Greater[W.`6`.T] = a
                                             ^

This mechanism allows to pass values of more specific types (e.g. Int Refined Greater[W.`10`.T]) to functions that take a more general type (e.g. Int Refined Positive) without manual intervention.

Note that W is a shortcut for shapeless.Witness which provides syntax for literal-based singleton types.

Table of contents

1. More examples
2. Using refined
3. Documentation
4. Provided predicates
5. Contributors and participation
6. Projects using refined
7. Performance concerns
8. Related projects
9. License

More examples

import eu.timepit.refined.boolean._
import eu.timepit.refined.char._
import eu.timepit.refined.collection._
import eu.timepit.refined.generic._
import eu.timepit.refined.string._
import shapeless.{ ::, HNil }

scala> refineMV[NonEmpty]("Hello")
res2: String Refined NonEmpty = Hello

scala> refineMV[NonEmpty]("")
<console>:39: error: Predicate isEmpty() did not fail.
            refineMV[NonEmpty]("")
                              ^

scala> type ZeroToOne = Not[Less[W.`0.0`.T]] And Not[Greater[W.`1.0`.T]]
defined type alias ZeroToOne

scala> refineMV[ZeroToOne](1.8)
<console>:40: error: Right predicate of (!(1.8 < 0.0) && !(1.8 > 1.0)) failed: Predicate (1.8 > 1.0) did not fail.
       refineMV[ZeroToOne](1.8)
                          ^

scala> refineMV[AnyOf[Digit :: Letter :: Whitespace :: HNil]]('F')
res3: Char Refined AnyOf[Digit :: Letter :: Whitespace :: HNil] = F

scala> refineMV[MatchesRegex[W.`"[0-9]+"`.T]]("123.")
<console>:39: error: Predicate failed: "123.".matches("[0-9]+").
              refineMV[MatchesRegex[W.`"[0-9]+"`.T]]("123.")
                                                    ^

scala> val d1: Char Refined Equal[W.`'3'`.T] = '3'
d1: Char Refined Equal[Char('3')] = 3

scala> val d2: Char Refined Digit = d1
d2: Char Refined Digit = 3

scala> val d3: Char Refined Letter = d1
<console>:39: error: type mismatch (invalid inference):
 Equal[Char('3')] does not imply
 Letter
       val d3: Char Refined Letter = d1
                                     ^

scala> val r1: String Refined Regex = "(a|b)"
r1: String Refined Regex = (a|b)

scala> val r2: String Refined Regex = "(a|b"
<console>:38: error: Regex predicate failed: Unclosed group near index 4
(a|b
    ^
       val r2: String Refined Regex = "(a|b"
                                      ^

scala> val u1: String Refined Url = "htp://example.com"
<console>:38: error: Url predicate failed: unknown protocol: htp
       val u1: String Refined Url = "htp://example.com"
                                    ^

Using refined

The latest version of the library is 0.8.1, which is available for Scala and Scala.js version 2.10, 2.11, and 2.12.

If you're using sbt, add the following to your build:

libraryDependencies ++= Seq(
  "eu.timepit" %% "refined"            % "0.8.1",
  "eu.timepit" %% "refined-pureconfig" % "0.8.1"  // optional, JVM-only
  "eu.timepit" %% "refined-scalacheck" % "0.8.1", // optional
  "eu.timepit" %% "refined-scalaz"     % "0.8.1", // optional
  "eu.timepit" %% "refined-scodec"     % "0.8.1", // optional
)

For Scala.js just replace %% with %%% above.

Instructions for Maven and other build tools are available at search.maven.org.

Release notes for the latest version are available in 0.8.1.markdown.

The optional dependencies are add-on libraries that provide support for other tag types or integration of refined types in other libraries:

• refined-pureconfig for PureConfig integration
• refined-scalacheck for ScalaCheck type class instances of refined types
• refined-scalaz for support of Scalaz' tag type (scalaz.@@)
• refined-scodec for scodec integration

See also the list of projects that use refined for libraries that directly provide support for refined.

Documentation

API documentation of the latest release is available at: http://fthomas.github.io/refined/latest/api/

There are further (type-checked) examples in the docs directory including ones for defining custom predicates and working with type aliases. It also contains a description of refined's design and internals.

Talks and other external resources are listed on the Resources page in the wiki.

Provided predicates

The library comes with these predefined predicates:

boolean

• True: constant predicate that is always true
• False: constant predicate that is always false
• Not[P]: negation of the predicate P
• And[A, B]: conjunction of the predicates A and B
• Or[A, B]: disjunction of the predicates A and B
• Xor[A, B]: exclusive disjunction of the predicates A and B
• Nand[A, B]: negated conjunction of the predicates A and B
• Nor[A, B]: negated disjunction of the predicates A and B
• AllOf[PS]: conjunction of all predicates in PS
• AnyOf[PS]: disjunction of all predicates in PS
• OneOf[PS]: exclusive disjunction of all predicates in PS

char

• Digit: checks if a Char is a digit
• Letter: checks if a Char is a letter
• LetterOrDigit: checks if a Char is a letter or digit
• LowerCase: checks if a Char is a lower case character
• UpperCase: checks if a Char is an upper case character
• Whitespace: checks if a Char is white space

collection

• Contains[U]: checks if a Traversable contains a value equal to U
• Count[PA, PC]: counts the number of elements in a Traversable which satisfy the predicate PA and passes the result to the predicate PC
• Empty: checks if a Traversable is empty
• NonEmpty: checks if a Traversable is not empty
• Forall[P]: checks if the predicate P holds for all elements of a Traversable
• Exists[P]: checks if the predicate P holds for some elements of a Traversable
• Head[P]: checks if the predicate P holds for the first element of a Traversable
• Index[N, P]: checks if the predicate P holds for the element at index N of a sequence
• Init[P]: checks if the predicate P holds for all but the last element of a Traversable
• Last[P]: checks if the predicate P holds for the last element of a Traversable
• Tail[P]: checks if the predicate P holds for all but the first element of a Traversable
• Size[P]: checks if the size of a Traversable satisfies the predicate P
• MinSize[N]: checks if the size of a Traversable is greater than or equal to N
• MaxSize[N]: checks if the size of a Traversable is less than or equal to N

generic

• Equal[U]: checks if a value is equal to U
• Eval[S]: checks if a value applied to the predicate S yields true
• ConstructorNames[P]: checks if the constructor names of a sum type satisfy P
• FieldNames[P]: checks if the field names of a product type satisfy P
• Subtype[U]: witnesses that the type of a value is a subtype of U
• Supertype[U]: witnesses that the type of a value is a supertype of U

numeric

• Less[N]: checks if a numeric value is less than N
• LessEqual[N]: checks if a numeric value is less than or equal to N
• Greater[N]: checks if a numeric value is greater than N
• GreaterEqual[N]: checks if a numeric value is greater than or equal to N
• Positive: checks if a numeric value is greater than zero
• NonPositive: checks if a numeric value is zero or negative
• Negative: checks if a numeric value is less than zero
• NonNegative: checks if a numeric value is zero or positive
• Interval.Open[L, H]: checks if a numeric value is in the interval (L, H)
• Interval.OpenClosed[L, H]: checks if a numeric value is in the interval (L, H]
• Interval.ClosedOpen[L, H]: checks if a numeric value is in the interval [L, H)
• Interval.Closed[L, H]: checks if a numeric value is in the interval [L, H]
• Modulo[N, O]: checks if a numeric value modulo N is O
• Divisible[N]: checks if a numeric value is evenly divisible by N
• NonDivisible[N]: checks if a numeric value is not evenly divisible by N
• Even: checks if a numeric value is evenly divisible by 2
• Odd: checks if a numeric value is not evenly divisible by 2

string

• EndsWith[S]: checks if a String ends with the suffix S
• MatchesRegex[S]: checks if a String matches the regular expression S
• Regex: checks if a String is a valid regular expression
• StartsWith[S]: checks if a String starts with the prefix S
• Uri: checks if a String is a valid URI
• Url: checks if a String is a valid URL
• Uuid: checks if a String is a valid UUID
• Xml: checks if a String is well-formed XML
• XPath: checks if a String is a valid XPath expression

Contributors and participation

• Alexandre Archambault (@alxarchambault)
• Chris Hodapp (@clhodapp)
• Dale Wijnand (@dwijnand)
• Frank S. Thomas (@fst9000)
• Jean-Rémi Desjardins (@jrdesjardins)
• Joe Greene
• John-Michael Reed
• Naoki Aoyama (@AoiroAoino)
• Shohei Shimomura (@sm0kym0nkey)
• Torsten Scholak (@tscholak)
• Viktor Lövgren (@vlovgr)
• Vladimir Koshelev (@vlad_koshelev)
• Your name here :-)

refined is a Typelevel project. This means we embrace pure, typeful, functional programming, and provide a safe and friendly environment for teaching, learning, and contributing as described in the Typelevel code of conduct.

Projects using refined

Please see the wiki for an incomplete list of projects and companies which use refined. If you are using the library and your project isn't listed yet, please add it.

Performance concerns

Using refined's macros for compile-time refinement has zero runtime overhead for reference types and only causes boxing for value types. Refer to RefineJavapSpec and InferJavapSpec for a detailed analysis of the runtime component of refinement types on the JVM.

Related projects

• SMT-Based Checking of Predicate-Qualified Types for Scala
• bond: Type-level validation for Scala
• F7: Refinement Types for F#
• LiquidHaskell: Refinement Types via SMT and Predicate Abstraction
• refined: Refinement types with static and runtime checking for Haskell. refined was inspired this library and even stole its name!
• refscript: Refinement Types for TypeScript
• Subtypes in Perl 6

License

refined is licensed under the MIT license, available at http://opensource.org/licenses/MIT and also in the LICENSE file.