On Wed, 15 Jun 2005, Rene de Visser wrote:
Hello,
I have a somewhat complicated calculation programmed in Haskell. This calculation is coded without using monads.
I want to also produce a report describing the details of this calculation for each particular set of inputs. e.g. Number of hours worked = 100. Gross pay per hour = 50. Total gross = 100 * 50 = 500.
Is this example computed with Excel? :-]
I think if I add the report generating functions into the calculation functions, it will make them twice as messy, and they are already complicated enough.
On the other hand replicating the calculation source code twice, once without reporting and once without seems bad.
I think that it is good style to separate computations from input/output operations and formatting. I suggest to divide the calculatoin into smaller parts. If you have more breaks you have more chances to get temporary results. You can put temporary values into a data structure. E.g. if you have an iteration don't write a recursion with a fixed abort criterion but write a function which maps the old value to the new one, then apply 'iterate' on it. Now you can inspect the temporary values and you can later apply a function which decides when to stop the iteration.