From: Hehe Nicht To: web-devel@haskell.org Date: Thu, 9 Jun 2011 11:26:14 +0200 Subject: withStmt function Could someone explain the withStmt function from Persist.Raw to me? Here is an example i was toying with:

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{-# LANGUAGE QuasiQuotes, TypeFamilies, GeneralizedNewtypeDeriving, TemplateHaskell, OverloadedStrings #-} import Database.Persist import Database.Persist.Base import Database.Persist.Sqlite import Database.Persist.GenericSql.Raw import Control.Monad.IO.Class (liftIO)

main :: IO () main = withSqliteConn ":memory:" $ runSqlConn $ do      _ <- execute "CREATE TABLE cities (name varchar(80),location point);" ([]::[PersistValue])      _ <- execute "INSERT INTO cities VALUES ('SanFrancisco','(100.0,100.9)');" ([]::[PersistValue])      _ <- execute "INSERT INTO cities VALUES ('New York','(1.0,10.9)');" ([]::[PersistValue])      query <- withStmt "SELECT name, location FROM cities;" ([]::[PersistValue]) (id)      liftIO $ print query

which prints "Just [PersistText "SanFrancisco",PersistText "(100.0,100.9)"])". So how do i get the rest of the rows? Do i have to pass a different function as the last argument to withStmt? Thanks in advance.

The function provided by withStmt returns one row at a time, until it exhausts the input and returns a Nothing. I'll try to write a "cookbook recipe" for the next cookbook installment describing that. Michael