Question

if reelID = reelWeights.Count - 1
    then Array.fold calc1 (0L,0) reelWeights.[reelID]
    else Array.fold calc2 (0L,0) reelWeights.[reelID]

I tried use pipeline, it seems to slow down a little bit (not sure why):

reelWeights.[reelID]
    |> (if reelID = reelWeights.Count - 1 then Array.fold calc1 else Array.fold calc2) (0L,0)

if I do

let calc x = if x then calc1 else calc2
Array.fold (calc reelID = reelWeights.Count - 1) (0L,0) reelWeights.[reelID]

then it looks nice at the cost of redundantly check conditionion in loops.

Answer 1

Assuming calc1 and calc2 have the same signature (or if they’re values rather than functions, are the same type):

let calc = if reelID = reelWeights.Count - 1 then calc1 else calc2
Array.fold calc (0L, 0) reelWeights.[reelID]