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|
-----------------------------------------------------------
-- |
-- Module : Query
-- Copyright : HWT Group (c) 2003, dp03-7@mdstud.chalmers.se
-- License : BSD-style
--
-- Maintainer : dp03-7@mdstud.chalmers.se
-- Stability : experimental
-- Portability : non-portable (requires Template Haskell)
--
-- Provides a Template Haskell function that declares
-- a HaskellDB field.
--
-- $Revision: 1.2 $
-----------------------------------------------------------
module THField (field, module Database.HaskellDB.DBLayout) where
import Database.HaskellDB.DBLayout
import Language.Haskell.THSyntax
-- | Declare a field.
field :: String -- ^ Haskell identifier for the field (e.g. "xid")
-> String -- ^ Actual field name (e.g. "id")
-> String -- ^ Name of the field label type (e.g. "Id")
-> Bool -- ^ Whether the field is nullable
-> String -- ^ Name of the value type of the field (e.g. "Int")
-> Q [Dec]
field attrName fieldName tagName nullable typeName
= return $ mkField attrName fieldName tagName nullable typeName
mkField :: String -> String -> String -> Bool -> String -> [Dec]
mkField attrName fieldName tagName nullable typeName =
[
mkTag tagName,
mkFieldTagInstance tagName fieldName,
mkAttrSig attrName tagName nullable typeName,
mkAttrVal attrName tagName
]
mkTag tagName = DataD [] tagName [] [NormalC tagName []] []
mkFieldTagInstance tagName fieldName =
InstanceD [] (AppT (ConT "FieldTag") (ConT tagName))
[FunD "fieldName"
[Clause [WildP] (NormalB (LitE (StringL fieldName))) []]]
mkAttrSig attrName tagName nullable typeName
= SigD attrName (AppT (AppT
(ConT "Attr")
(ConT tagName)) (mkType nullable typeName))
mkType nullable typeName = if nullable then AppT (ConT "Maybe") t else t
where t = ConT typeName
mkAttrVal attrName tagName =
ValD (VarP attrName) (NormalB
(AppE (VarE "mkAttr")
(ConE tagName))) []
|
