haskell - No instance for Database.SQLite.Simple.FromField.FromField Char -

this code gives me error:

67:    isfileinstalled f = 68:                dbcon <- open "/var/lib/beaver/pkgs.db" 69:                res <- querynamed dbcon "select * files path = :path" [":path" := ("/usr/bin/getpkg" :: string)] 70:                mapm_ putstrln res 71:                -- when (null res) (return ()) 72:                -- putstrln ("file " ++ res ++ " installed , comes " ++ res ++ ".") -- first res `owner` , second `path` 73:                close dbcon 74:                exit 

i error:

no instance (database.sqlite.simple.fromfield.fromfield char)      arising use of `querynamed'    in stmt of 'do' block:      res <- querynamed               dbcon               "select * files path = :path"               [":path" := ("/usr/bin/getpkg" :: string)]    in expression:      { dbcon <- open "/var/lib/beaver/pkgs.db";           res <- querynamed                    dbcon                    "select * files path = :path"                    [":path" := ("/usr/bin/getpkg" :: string)];           mapm_ putstrln res;           close dbcon;           .... }    in equation `isfileinstalled':        isfileinstalled f          = { dbcon <- open "/var/lib/beaver/pkgs.db";                 res <- querynamed                          dbcon                          "select * files path = :path"                          [":path" := ("/usr/bin/getpkg" :: string)];                 mapm_ putstrln res; 

i didn't find in google. if it's important, overloadedstrings enabled. there workaround (or way fix it)?

you using res [string]:

mapm_ putstrln res 

it equivalent [[char]]. querynamed returns list of rows, each row has type [char]. there instance fromfield => fromrow [a], there no instance fromfield char. error messages says.

i never used sqlite-simple, clear each row contains number of fields, trying fetch row contains number of fields of type char. makes no sense. depending on actual database scheme, each row should e.g. number of text field, res can have type [[string]]. in case should use next:

mapm_ (mapm_ putstrln) (res :: [[string]])