SemVer.ghci

λ> parseString parseSemVer mempty "1.0.0-alpha+001"
Success (SemVer 1 0 0 [NOSS "alpha"] [NOSI 1])
λ> parseString parseSemVer mempty "1.0.0+20130313144700"
Success (SemVer 1 0 0 [] [NOSI 20130313144700])
λ> parseString parseSemVer mempty "1.0.0"
Success (SemVer 1 0 0 [] [])

SemVer.hs

module SemVer where

import Text.Trifecta
import Control.Applicative

data NumberOrString = NOSS String | NOSI Integer deriving (Show, Eq, Ord)
type Major = Integer
type Minor = Integer
type Patch = Integer
type Release = [NumberOrString]
type Metadata = [NumberOrString]
data SemVer = SemVer Major Minor Patch Release Metadata deriving (Show, Eq, Ord)

parseSemVer :: Parser SemVer
parseSemVer = do
  major <- integer
  _     <- char '.'
  minor <- integer
  _     <- char '.'
  patch <- integer
  release  <- try (char '-' *> parseReleaseOrMetadata) <|> pure mempty
  metadata <- try (char '+' *> parseReleaseOrMetadata) <|> pure mempty
  return $ SemVer major minor patch release metadata

parseNumberOrString :: Parser NumberOrString
parseNumberOrString = (NOSI <$> integer) <|> (NOSS <$> (some letter))

parseReleaseOrMetadata :: Parser [NumberOrString]
parseReleaseOrMetadata =
  ((:) <$> (try (parseNumberOrString <* char '.'))
    <*> parseReleaseOrMetadata) <|>
    pure <$> parseNumberOrString