Back to Questions
966
views1
comment
Sequence / List confusion
f#

Hi, in the following example, excel.Rows is implemented in C# und returns an IEnumerable<EXCELROW>. When I execute the code, I the the following error: C:\...\compare.fsx(22,7): error FS0193: Type constraint mismatch. The type seq<EXCELROW> is not compatible with type string list. The type 'seq<EXCELROW>' is not compatible with the type 'string list'. I understand the error message, but I have no idea how to fix it!? Any help would be very appreciated. cheers, Achim

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23

use excel = new Excel("data.xlsx")

let idMapping = "data.csv" |> CsvTools.Read

let status (id: string) =

    let s = Seq.tryfind (fun row -> row.[0]=id) idMapping

    match s with

        | None -> "missing"

        | Some a -> "ok"

let rec check (rows) =

    match rows with

        |h::t -> printfn "%s" (status h); check t

        |_ -> None

check excel.Rows
.

Your match statement that matches h::t expects a list. You could change the 'check' function to use a 'for' loop, which iterates over seqs (e.g.

for x in rows do

printfn "%s" (status x)

) or you can use (List.of_seq excel.Rows) to turn that value into a list before passing it to the function. The former is probably easier/better, if all you want to do is iterate over the values, using seq data and a for loop to iterate over it is fine, no need to convert data structures.

Note that 'seq' type in F# is just shorthand for 'IEnumerable'.

By on 12/17/2008 8:10 AM ()

    Topic tags

    IntelliFactory Offices Copyright (c) 2011-2012 IntelliFactory. All rights reserved.
    Home | Products | Consulting | Trainings | Blogs | Jobs | Contact Us | Terms of Use | Privacy Policy | Cookie Policy     		Built with WebSharper