On Thu, Feb 18, 2010 at 3:36 PM, Richard Newman <holyg...@gmail.com> wrote:
> You express the equations as functions. Turning your equation notation into
> function notation -- I'll use Haskell's as an example:
>
> OpportunityCost = Rent - Sell
>
> becomes
>
> opportunityCost r s = r - s
>
> or in Clojure:
>
> (defn opportunity-cost [r s]
> (- r s))
What to do if we don't know which of the equation variables are
unknowns? Let's say that the user may choose whether to input "Rent"
and "Sell", or "Rent" and "opportunityCost". I can imagine writing
some code like this:
(defn opportunity-cost [opportunity-cost-in rent-in sell-in]
(if (nil? opportunity-cost-in)
(- rent-in sell-in)
opportunity-cost-in))
(defn rent [opportunity-cost-in rent-in sell-in]
(if (nil? rent-in)
...)
(defn sell [opportunity-cost-in rent-in sell-in]
(if (nil? sell-in)
...)
but complexity of such expressions quickly grows as dependencies
between variables become more complex. Is there any
technique/framework for handling such calculations automatically? I
have a vague impression that this is what logic programming languages
are about. How would one implement such calculations in Clojure?
Going further, what to do if the equation is underspecified (for
example, if the user has only input "Rent") and we want to do
something more useful than just fail. This would require us to do the
calculations symbolically. Can Clojure help here somehow? What would
be a minimal CAS framework in Clojure?
-Andrzej
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