+httpVersionP ∷ Parser HttpVersion
+httpVersionP = string "HTTP/"
+ ≫
+ choice [ string "1.1" ≫ return (HttpVersion 1 1)
+ , string "1.0" ≫ return (HttpVersion 1 0)
+ , do major ← decimal
+ _ ← char '.'
+ minor ← decimal
+ return $ HttpVersion major minor
+ ]