Calculator for magic item creation in RPG

Question

I have created a simple calculator that will assist in creating magic items from the tabletop RPG Pathfinder. Here are the full requirements, and if you want a more concise version, here is a player generated summary of the process.

I have been trying to get into F# and functional programming in general. I come from a strong object-oriented background and it has been difficult in ignoring those habits. Please focus on whether or not this is idiomatic F#. I would love to hear if there is a better way to write any of it. And, if you find bug, I'd be happy to know that too.

Questions

A couple of things specifically that I feel could be better would be the DC calculation. I wasn't sure how to approach applying the rush function only if the item was rushed. I also tried finding a place where I could apply functional composition, but I think I needed all the intermediate steps that I stop on.

Code

let baseDC casterLevel =
 5 + casterLevel
let rush dc =
 dc + 5
let ignoreRequirements requirements dc =
 dc + (5 * requirements)
let getBuildPrice basePrice =
 basePrice * 0.5
let getTime basePrice =
 floor (8.0 * basePrice / 1000.0)
let getMinBonusForNoCursed dc =
 dc - 6
let buildDaysWhileAdventuring isRushed buildTime =
 let adventuringBuildTime = buildTime / 4.0
 floor (if isRushed then adventuringBuildTime else adventuringBuildTime * 2.0)
[<EntryPoint>]
let main argv = 
 printfn "%A" argv
 let isRushed = true
 let casterLevel = 1
 let requirementsIgnored = 1
 let basePrice = 5000.0
 let buildPrice = getBuildPrice basePrice
 let buildTime = getTime basePrice
 let daysAdventuring = buildDaysWhileAdventuring isRushed buildTime
 let DC = 
 match isRushed with
 | false -> baseDC casterLevel |> ignoreRequirements requirementsIgnored
 | true -> baseDC casterLevel |> ignoreRequirements requirementsIgnored |> rush
 let minDC = getMinBonusForNoCursed DC
 printfn "Min/DC: %i/%i Cost: %.2f Days/Hours: %.1f/%.1f" minDC DC
 buildPrice daysAdventuring buildTime
 0 // Return code

Answer 1

I see a few problems with this, most notably, you have a plethora of magic numbers.

let baseDC casterLevel =
 5 + casterLevel
let rush dc =
 dc + 5
let ignoreRequirements requirements dc =
 dc + (5 * requirements)
let getBuildPrice basePrice =
 basePrice * 0.5
let getTime basePrice =
 floor (8.0 * basePrice / 1000.0)
let getMinBonusForNoCursed dc =
 dc - 6
let buildDaysWhileAdventuring isRushed buildTime =
 let adventuringBuildTime = buildTime / 4.0
 floor (if isRushed then adventuringBuildTime else adventuringBuildTime * 2.0)

In order, I see:

1. 5 + casterLevel: what is 5?
2. dc + 5: what is 5? Is it the same as #1?
3. 5 * requirements: what is 5? Is it the same as #1 or #2?
4. basePrice * 0.5: what is 0.5? Is it 1 / 2 or something different?
5. 8.0 * basePrice: what is 8.0?
6. #5 / 1000.0: what is 1000.0?
7. dc - 6: what is 6?
8. buildTime / 4.0: what is 4.0?
9. adventuringBuildTime * 2.0: what is 2.0, is it 4.0 / 2, is it the 4.0 from #8 / 2?

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For a functional program, it's not too bad. I don't like how many times you use if (I always prefer match), but when dealing with boolean types it does quite fine.