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u/Emotional-Magician87

r/Kotlin
kexpresso – fluent Kotlin DSL that makes regex readable (KMP, on Maven Central, 0% overhead)
▲ 14 r/Kotlin

kexpresso – fluent Kotlin DSL that makes regex readable (KMP, on Maven Central, 0% overhead)

Hi r/Kotlin,

I just shipped kexpresso 0.8.0 to Maven Central. It's a small library I built because I got tired of writing regexes I couldn't read a week later. Sharing it here in case it scratches the same itch for someone — and to get API feedback before I commit to 1.0.

The pitch

Raw regex:

val email = Regex("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}")

kexpresso:

val email = kexpresso {
    startOfText()
    email()
    endOfText()
}

Same semantics. The DSL compiles to a standard kotlin.text.Regex at construction time — I measured 0% match-time overhead vs raw Regex.

What's interesting

Beyond the builder, four features that came out of dogfooding:

  • describe() — walks an internal AST of your pattern and returns a plain-English explanation. Useful when you inherit someone else's regex.
  • analyze() — static analysis that flags ReDoS-vulnerable shapes (nested quantifiers, ambiguous alternations). Catches "catastrophic backtracking" before prod.
  • examples(count, seed) — generates strings that match the pattern. Deterministic per seed, AST-driven. Great for test data.
  • Kexpresso.from(regex) — reverse-engineers a raw regex into the DSL. Round-trippable for the supported subset.

Plus 16 domain helpers (email(), ipv4(), ipv6(), url(), uuid(), base64(), jwt(), macAddress(), etc.) and typed named-captures.

Multiplatform

Full DSL lives in commonMain. Published targets: JVM, JS (IR/Node), wasmJs, linuxX64, mingwX64, macosX64/Arm64, iosArm64/X64/SimulatorArm64. The Wasm/JS Regex engine accepts the full portable test suite identically to JVM; JVM-only constructs (\A, \z, atomic groups, possessive quantifiers) stay JVM-only and remain tested there.

Install

implementation("io.github.elzinko:kexpresso:0.8.0")

No token, no extra repo config — it's on Maven Central. GitHub Packages and JitPack are alternatives.

Honest disclaimers

  • Still 0.x. Public API is reasonably stable but I want external feedback before promising SemVer 1.0.
  • examples(n) is best-effort on Raw nodes (domain helpers, Kexpresso.from()), lookarounds, and backreferences — generation never throws but those constructs may not produce a guaranteed match.
  • Not a regex engine — it's a builder + analyzer on top of kotlin.text.Regex.

Links

Specifically looking for feedback on:

  1. Anything in the public API you'd regret if it were frozen at 1.0?
  2. Domain helpers I should add (or remove)?
  3. KMP target coverage gaps you hit?

Roast away — that's what 0.x is for.

u/Emotional-Magician87 — 9 hours ago