semver.nim

import pegs, strutils

type
  TSemVer* = tuple
    major, minor, patch: system.Natural
    special: string

proc toSemVer*(versionString: string): TSemVer {.noSideEffect.} =
  if versionString =~ peg"{\d+} \. {\d+} \. {\d+} {.*}":
    var
      major: system.Natural = matches[0].ParseInt
      minor: system.Natural = matches[1].ParseInt
      patch: system.Natural = matches[2].ParseInt
      special = matches[3]
    result = (major, minor, patch, special)
  else:
    raise newException(ESystem, "Invalid version string")

proc `$`*(version: TSemVer): string =
  result = join([$version.major, $version.minor, $version.patch], ".")
  if version.special.len > 0: result.add  "-" & version.special

when isMainModule:
  # This doesn't work
  const VERSION = "1.23.4".toSemVer
  echo(VERSION)

  # But this works
  var v1 = "1.23.4".toSemVer
  echo(v1)