Mapping an array of strings to an array of strings

Question

I'm getting this error when I try to compile

The operator 'expr.[idx]' has been used on an object of indeterminate type based on information prior to this program point. Consider adding further type constraints

This is the code

let convertFile fileName =
    let arrayToTransaction (arr: string[]) =
        arr 
        |> Array.map (fun x -> splitStr [|"\n"|])
        |> Array.map 
            (fun x -> { 
                        date = DateTime.Parse(x.[1]);
                        payee = x.[0].Substring(0, x.[0].IndexOf(','))
                        category = "Everyday Expenses: Groceries/Food"
                        memo = "Parsed with my F# parser"
                        outflow = Single.Parse(x.[2].Substring(str.IndexOf('-') + 1))
                        inflow = 0.0f
                      })

John Palmer · Accepted Answer · 2014-11-06 21:11:23Z

1

The solution is to do exactly what the error message says, and add a type annotation:

|> Array.map 
            (fun (x:string[]) -> { 
                        date = DateTime.Parse(x.[1]);
                        payee = x.[0].Substring(0, x.[0].Index

answered Nov 6, 2014 at 21:11

John Palmer

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4 Comments

Overly Excessive Over a year ago

That doesn't work, unfortunately, it says. This expression was expected to have type string -> string [] but here has type string []. Which doesn't make a lot of sense to me because the array is a collection of strings..

scrwtp Over a year ago

the problem is your splitStr call one line earlier. You're not passing in the x string at all.

Overly Excessive Over a year ago

Yes I figured it out literally the same time as you posted. I thought the lambda would "pipe" the x to splitStr alas it doesn't it seems.

John Palmer Over a year ago

Note: This is why it is a good idea to give line numbers of errors

Overly Excessive · Accepted Answer · 2014-11-06 21:27:21Z

0

I figured it out, the problem was this line

    |> Array.map (fun x -> splitStr [|"\n"|])

Because splitStr is a helper function that takes two arguments, however I thought that the lambda would "pipe" the x into it but it doesn't work that way I noticed so changing it to this worked.

    |> Array.map (fun x -> splitStr [|"\n"|] x)

answered Nov 6, 2014 at 21:27

Overly Excessive

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1 Comment

scrwtp Over a year ago

Right, nothing of that sort gets done implicitly. You can make it point-free if you do this though: Array.map (splitStr [|"\n"|]).

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