gistfile1.hs

module Rules where

Schema ( "time"    =: timestamp
       , "enabled" =: bool )

data Value = VInt    Int
           | VString String
           | VBool   Bool
           | VList   [Value]
           | VSchema [(String, Value)]
           | VFail   Value Rule

type Rule = Check (Value -> Value) String
          | AnyOf [Rule]
          | ForAll Rule

isFail :: Value -> Bool
isFail (VFail _ _) = True
isFail _           = False

bool :: Rule
bool = Check isBool "must be boolean" where
  isBool (VBool x) = VBool x
  isBool x         = VFail x bool

str :: Rule
str = Check isStr "must be a string" where
  isStr (VString x) = VString x
  isStr x           = VFail x str

numeric :: Rule
numeric = Check isNum "must be a number" where
  isNum (VInt x) = VInt
  isNum x        = VFail x numeric