Re: Determining which functions to call

[Björn De Meyer <bjorn.demeyer@...>]

Florian Berger wrote:
> 
> Hi.
> 
> I would like to make a script system which determines the order of needed
> function calls to solve a problem. The basic idea is that I know values of
> some variables and then I have functions which can or cannot solve the
> problem with existing variables.
> 
> Simple example:
> I have a Circle-object which has two attributes: radius and diameter.
> I know the circle's radius but not the diameter.
> I have two functions: one which calculates diameter from radius and other
> which calculates area of circle using diameter.
> I would like to make my system solve the area of circle so, that it
> automatically solves the diameter for the area-function.
> 
> Are there some examples of this kind of problems for LUA and do you think
> LUA is good choice for this kind of programming?
> 
> Florian

This would be quite simple: 
(Lua 5 beta code, I think it's PI in stead of math.pi in Lua 4)

function areafromdiameter(d)
   return math.pi * d * d / 4
end

function calccircle(circle)
  if circle.radius then --will be false if not defined.
     circle.diameter = circle.radius * 2
  end
  return areafromdiameter(circle.diameter)
--This skips certain sanity checks that might be useful
end

print(calccircle({radius=4}))
print(calccircle({diameter=8}))

--Outputs:
--50.265482457437
--50.265482457437 

-- 
"No one knows true heroes, for they speak not of their greatness." -- 
Daniel Remar.
Björn De Meyer 
bjorn.demeyer@pandora.be