forgot to CC list.
---------- Forwarded message ----------
From: David Barbour <dmbarb...@gmail.com>
Date: 2011/9/6
Subject: Re: [Haskell-cafe] Is there any way to parametrize a value update
using record syntax?
To: Poprádi Árpád <popradi_ar...@freemail.hu>
2011/9/6 Poprádi Árpád <popradi_ar...@freemail.hu>
> But it's ugly. Always the same, only the record selector has another
> name. Is it possible to generalize it?
>
You can generalize using template haskell. I believe Oleg's HList already
provides such mechanisms, so you don't need to do this yourself. If you're
doing this a lot, try the HList package. (If not, just do the
Also, I would say you've too tightly coupled your BigData to the MonadicEnv.
I suggest you reduce it instead to:
setX :: X -> BigData -> BigData
setX x' bd = bd { dataX = x' }
updX :: (X -> X) -> BigData -> BigData
updX fx bd = bd { dataX = fx (dataX bd) }
Then in your state monad you can use:
modify (setX x')
gets dataX
And use of 'updX' is much more composable.
That aside, from personal experience, I'm usually okay just using:
modify (\ s -> s { dataX = x' })
in the few places I need it.
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