On 4/18/13 10:16 AM, glen wrote:
When you pick up a rock and use it as a hammer, what is the satisfied
predicate? It's certainly not "hammer(x)", because rocks are usually
nothing like hammers.
An object with high mass and volume, low acceleration vs. low mass, low
volume, and high acceleration?
Even if you have a type that simply tracks physical properties, it can
be embedded in other objects.
data PhysicalProperties = PhysicalProperties Mass Volume Location
data Hammer = Hammer PhysicalProperties
data Rock = Rock PhysicalProperties
or tagged instances..
data Tag = Hammer | Rock
data PhysicalProperties = PhysicalProperties Mass Volume Location Tag
hammer = PhysicalProperties 1 1 (0,0,1) Hammer
rock = PhysicalProperties 0.5 0.5 (0,0,0) Rock
mass :: PhysicalProperties -> Mass
mass (PhysicalProperties mass _ _) = mass
isCrushed :: PhysicalProperties -> Bool
isCrushed (PhysicalProperties _ volume _) = volume < 1e-6
impact :: PhysicalProperties -> PhysicalProperties >
(Bool,PhysicalProperties,PhysicalProperties)
If you want to have both physical realism and rules, then decouple them
using a physics engine.
Let the physics engine move the objects around but have rules embedded
in the objects be unaware of physical properties..
Marcus
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