[database-devel] Postgresql enum type conversions

Luke Hoersten luke at hoersten.org
Sat Jun 16 21:02:16 CEST 2012

I'm trying to use postgresql enum types to represent Haskell types
like in the code snippet below but an receiving the following error:

"Incompatible {errSQLType = "x", errHaskellType = "Text", errMessage =
"types incompatible"}"

In other areas of my code (not shown) I'm successfully using Text to
convert to and from Postgersql enum types but it doesn't seem to work
in the case below. Any ideas what I'm doing wrong?

Thanks, Luke

import           Database.PostgreSQL.Simple.FromField
(FromField, fromField)import
Database.PostgreSQL.Simple.FromRow          (FromRow, field,
fromRow)import           Database.PostgreSQL.Simple.SqlQQ

data X = X Float
       | Y Float

buildX :: Text -> Float -> XbuildX "x"      = XbuildX "y"      = Y

instance FromField (Float -> X) where
    fromField f v = buildX <$> fromField f v

instance FromRow X where
    fromRow = field <*> (field :: RowParser Float)
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