CODEWITHSUNDEEP
f#
Steven
Steven

Reputation: 3292

Functions with lines that read in other data files

I have a console app that has an example function:

let aFxUsedFromTheEntryPoint () = 
    let aHelperFx (cThing) (iThing) (qThing) = 
        Unchecked.defaultof<Quote>

    let c = 
        thisFx() //this line reads in and process lots of data; takes some time

    let i = 
        thatFx() //this line also reads in and processes lots of data; takes some time

    aList
    |> List.map (fun q -> aHelperFx c i q)

How are the c and i variables used in the function? Are they read in once before last two lines and just used repeatedly, for however long aList is? Or are they executed once for every q in `aList'?

If the latter, is there a better way to go about writing a function like this? Can I somehow write the function so that c and i are run only once, yet passed however many times it's necessary in aList?

Upvotes: 2

Views: 80

Answers (2)

Gus
Gus

Reputation: 26184

The most obvious solution is to move them out of the function body:

let c = thisFx() //this line reads in and process lots of data; takes some time
let i = thatFx() //this line also reads in and processes lots of data; takes some time

let aFxUsedFromTheEntryPoint () = 
    let aHelperFx (cThing) (iThing) (qThing) = Unchecked.defaultof<Quote>
    aList |> List.map (fun q -> aHelperFx c i q)

Typically if your function is declared inside a module, then those two let bindings can be declared at the same level as the function, in this case at the module level.

This is the first thing I will consider. Now if you want them to be called the first time the aFxUsedFromTheEntryPoint function is called then you can use other techniques like memoization or the lazy value as explained in the other answer, but note that the first call to the function will be slower than the subsequent calls.

Upvotes: 2

s952163
s952163

Reputation: 6324

Maybe wrapping it into lazy will help? 

let x4 = lazy (
            printfn "%A" "Long Running stuff"
            let addX (x:int) = x + 1   
            addX)
//val x4 : Lazy<(int -> int)> = Value is not created.
let c = x4.Force() 4
//"Long Running stuff"
//val c : int = 5
c // val it : int = 5
c

Upvotes: 0

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