[Haskell-cafe] Linear programming in Haskell

Louis Wasserman wasserman.louis at gmail.com
Mon Mar 1 19:46:10 EST 2010

If you're using the LPM monad, then this is about as easy as that: you use

do    (x1:x2:x3:_) <- newVariables

I mean, run is equivalent to

run f = execLPM (newVariables >>= put . f)

so...yeah, I think this is a reasonable solution.

Alternatively, I'm almost positive there's a monad out there that lets you
draw on unique values.  It'd look something like

type Variable = Int
newtype UniqueM a = UniqueM (Variable -> (Variable, a))

-- monad instance, etc.

getUnique :: UniqueM Variable
getUnique = UniqueM (\ x -> (x+1, x))

Then you can use the LPT monad transformer to construct a linear program
around this, just by working in the "LPT Variable c UniqueM" monad.

That's actually a nicer solution than my current implementation.  I'll do
that, then...

Louis Wasserman
wasserman.louis at gmail.com

On Mon, Mar 1, 2010 at 9:29 AM, Henning Thielemann <
lemming at henning-thielemann.de> wrote:

> On Sun, 28 Feb 2010, Louis Wasserman wrote:
>  It's an expensive operation, though -- since I don't track the set of all
>> variables as the LP is built, I need to construct the set of all variables
>> before generating new ones -- so it's recommended that you get all the
>> variables you need in one or two passes.
> Then you might prefer a single operation that generates all variables and
> runs an enclosed problem on them:
> run :: ([Variable] -> LP a) -> LP a
> Use as
> run $ \x0:x1:x2:_ -> do
>   ...
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