scalacheck-gen-regexp

A library for creating scalacheck generators from regular expressions

Cross-built for Scala 2.12/2.13/3.1/3.2

In your build.sbt

libraryDependencies += "io.github.wolfendale" %% "scalacheck-gen-regexp" % "[VERSION]"

import wolfendale.scalacheck.regexp.RegexpGen

val generator: Gen[String] = RegexpGen.from("[1-9]\\d?(,\\d{3})+")

Feature	Example	Notes
Literals	`a`, `\\w`, `7`	Literals are transformed into constant generators
Character Classes	`[abc]`, `[^abc]`, `[a-zA-Z0-9]`	Character classes are transformed with `Gen.oneOf`
Default Classes	`\w`, `\d`, `\S`, `.`	These are treated as predefined character classes
Quantifiers	`a?`, `b+`, `c*`, `d{3}`, `e{4,5}`, `f{5,}`	These use `Gen.listOfN` to create sized lists of the preceding term
Groups	`(abc)`, `(?:def)`	Backreferences are not supported, groups can only be used for grouping terms
Alternates	`a\|b\|c`, `a(b\|c)d`	Alternates are also transformed with `Gen.oneOf`
Boundaries	`^`, `$`, `\b`	Although these will be parsed they do not modify the generator output

Feature	Example	Notes
Backreferences	`([ab]\1)`	With the current implementation there's no simple way to do this, definitely in consideration for a future release
Octal / Hex / Special Literals	`\012`, `\xF1`, `\p{Lower}`	Most of these should be simple to implement but I wanted to get an initial release created first
Character Class Intersection	`[a&&[b]]`, `[a[b]]`	Difficult to implement currently but not impossible, definite consideration for a future release

In order to represent any character, RegexpGen#from takes an implicit Arbitrary[Char]. There is a default instance provided by scalacheck however for most uses you probably want to provide your own.
If you use the + or * quantifiers you'll end up getting huge variance in string sizes. If this isn't what you want, consider bounding the lengths of certain string segments with the {min,max} quantifier.
Negated character classes / default classes are implemented by generating an arbitrary Char within certain bounds via suchThat, because of this you can end up throwing away a lot of cases and in certain circumstances your tests may fail. Try to refactor out negative cases.
In character classes each option is given equal weighting. If you'd prefer to weight a particular entry you can add it multiple times, this is made easier with string interpolation: s"[${"a-z"*5}\s]". In the example case the generator is 5 times more likely to generate an alpha character than a space.

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