On 14/12/11 13:59, Marc Weber wrote:
Excerpts from Michael Snoyman's message of Wed Dec 14 14:34:30 +0100 2011:
On Wed, Dec 14, 2011 at 3:31 PM, C K Kashyap<[email protected]> wrote:
Definite *don't* use read/show: if you make any updates to your data
structures, all old files will be lost.
Well you can work around it:
data MyDataV1 = {
name :: String
}
deriving (Read,Show)
then you make an update:
data MyDataV2 = {
name :: String,
age : Int
}
deriving (Read,Show)
then you can do
let (v1 :: MyDataV1) = tryReadDataToMaybe data
let (v2 :: MyDataV2) = tryReadDataToMaybe data
let real_data = upgrade v1 `or` v2
But you already see that you start writing boilerplate code.
It can be done for easy data structures .. But it soon will be a night
mare if you have complex data.
If you use a version control system you don't loose your data - it will
just be "hard to update".
[snip]
I ran into this very nightmare in one project, and was recommend
safecopy [0] by someone on the #haskell IRC channel. I've not (yet)
used it but it looks very nice!
[0] http://hackage.haskell.org/package/safecopy
Claude
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