# [Haskell-cafe] Fuzzy Logic / Linguistic Variables

Neal Alexander relapse.dev at gmx.com
Wed Oct 14 08:59:54 EDT 2009

```So i was reading "Programming Game AI by Example" by Mat Buckland
(http://www.ai-junkie.com/books/toc_pgaibe.html) and decided to rewrite
his chapter on Fuzzy logic in haskell (from C++).

My initial impression: its one of those scenarios where OOP grossly over
complicates things

Heres an example taken from the book: An agent needs to decide what
weapon to use based on his distance from the target and the amount of
ammo each has. The result is in the desirability domain (0-100).

An excerpt:

------------------------------------

weapons = [ Weapon "RocketLauncher" 9 rocketLauncher,
Weapon "ShotGun" 13 shotgun,
Weapon "AssaultRifle" 120 assaultRifle,
Weapon "SniperRifle" 7 sniperRifle,
Weapon "Knife" 1 knife ]

chooseWeapon dist = maximum ratings
where
ratings = [ (f dist ammo, n) | Weapon n ammo f <- weapons ]

------------------------------------

shotgun :: Double -> Double -> Double
shotgun dist ammo =

unfuzz desireDom \$ rules (fuzz distDom dist) (fuzz ammoDom ammo)

where

rules :: Fuzzy Distances -> Fuzzy Ammo -> FL Desirability
rules distance ammo = do

distance `is` SniperSuited =>> Pointless
distance `is` Far          =>> Undesirable
distance `is` Medium       =>> Undesirable
distance `is` Melee        =>> Undesirable

(distance `fairly` Near) & (ammo `fairly` High) =>> VeryDesirable
(distance `fairly` Near) & (ammo `fairly` Good) =>> Desirable
(distance `fairly` Near) & (ammo `is` Low)      =>> Undesirable

------------------------------------

Suggestions welcome - maybe it'd be useful to upload to hackage at some
point.

It only supports triangle, shoulder, and singleton memberships at the
moment.

```