+ -- Optimisation for special cases.
+ HttpVersion 1 0 → A.toAsciiBuilder "HTTP/1.0"
+ HttpVersion 1 1 → A.toAsciiBuilder "HTTP/1.1"
+ -- General (but almost never stumbling) cases.
+ HttpVersion maj min
+ → A.toAsciiBuilder "HTTP/" ⊕
+ A.toAsciiBuilder (A.unsafeFromString $ show maj) ⊕
+ A.toAsciiBuilder "." ⊕
+ A.toAsciiBuilder (A.unsafeFromString $ show min)
+
+-- |'Parser' for an 'HttpVersion'.
+httpVersion ∷ Parser HttpVersion
+httpVersion = string "HTTP/"
+ *>
+ (HttpVersion <$> decimal ⊛ (char '.' *> decimal))