How is it possible that the F# compiler rejects the type string when it's expecting a System.String?
#I #"..\..\packages"
#r #"FSharp.Data\lib\net40\FSharp.Data.dll"
open FSharp.Data
let [<Literal>] csvFile = #"..\..\data\FootballResults.csv"
type Football = CsvProvider< csvFile >
let data = Football.GetSample().Rows |> Seq.toArray
After running this simple code, I get the error message:
Script.fsx(5,30): error FS0001: This expression was expected to have type 'System.String' but here has type 'string'
I thought string was simply an alias for System.String?
Edit
The csv file is quite big, just the first rows are important:
Date,Home Team,Away Team,Full Time Home Goals,Full Time Away Goals,Full Time Result,Half Time Home Goals,Half Time Away Goals,Half Time Result,Home Shots,Away Shots,Home Shots on Target,Away Shots on Target,Home Fouls,Away Fouls,Home Cards,Away Cards,Home Yellow Cards,Away Yellow Cards,Home Red Cards,Away Red Cards
08/18/2012,Arsenal,Sunderland,0,0,D,0,0,D,14,3,4,2,12,8,7,0,0,0,0,0
08/18/2012,Fulham,Norwich,5,0,H,2,0,H,11,4,9,2,12,11,6,3,0,0,0,0
08/18/2012,Newcastle,Tottenham,2,1,H,0,0,D,6,12,4,6,12,8,3,5,2,2,0,0
The full file can be downloaded here under the folder data
FSharp.Data version
FSharp.Data 2.3.2
I found the problem, it was in the paket script provided in the book Get Programming with F#.
The script was pointing to an old version of FSharp.Data (I thought paket was this amazing package manager that always get you the best version for your project while in fact, it does not, you always fight and struggle with wrong dependencies).
At the end I managed to fix the problem this way:
Solution 1
Simply start a new project using the nuget command Install-Package FSharp.Data -Version 4.2.7 and then the reference to the package #r "nuget: FSharp.Data"
Solution 2
Update the paket.lock provided by the book with the correct version FSharp.Data (4.2.7). The code posted in my question run after that.
Advice for F# learner
Whoever is trying to learn F# with this book, it's a good book but be very careful with their package reference. They seem outdated and can get you into unpleasant situation.
If I compile some code with the following:
#include <string_view>
std::string_view strv{ "Test 1" };
I get this error:
Error C2065 'string_view': undeclared identifier...
I tried some other c++17 code and not of it works.
I get the same errors if the C++ Language Standard is set to std:c++14
The Properties-->C/C++-->Command line contains /std:c++17
but the actual compiler command line that runs does not have this option set.
This is a community version of Visual Studio 2019 version 16.7.1
user dxiv pointed out the problem is in the Property pages Platform pulldown it should be set to ALL Platforms (or set C++17 individually for Win32 and x64 platforms).
I am writing a service using .net Core with Visual Studio 2017. I want to use JSON for the configuration, so I defined my type like this:
type ServiceConfig = JsonProvider<"exampleConfig.json", EmbeddedResource="MyService, exampleConfig.json", SampleIsList = true>
In my program, I load it like this:
let conf = ServiceConfig.Load "config.json"
When I run it, it works fine, but in VS 2017 I get a red squiggly line and the error log says:
FS3033 The type provider 'ProviderImplementation.JsonProvider'
reported an error in the context of provided type
'FSharp.Data.JsonProvider,Sample="exampleConfig.json",SampleIsList="True",EmbeddedResource="MyService, exampleConfig.json"', member 'Load'. The error: Method
'FSharp.Data.Runtime.BaseTypes.IJsonDocument
Create(System.IO.TextReader, System.String)' not found in type
''. This method may be missing in the types available in the
target assemblies.
How do I get rid of this?
I'm not sure that this is the problem, but it might help to give an absolute path of the sample file. Resolving a relative path is a constant source of issues in type providers. You can do something like:
[<Literal>]
let sample = __SOURCE_DIRECTORY__ + "/exampleConfig.json"
type ServiceConfig =
JsonProvider< sample, EmbeddedResource="MyService, e
xampleConfig.json", SampleIsList = true >
By chance I found the answer myself. It must have been some Visual Studio index having gone wonky. I had another problem with another project in my solution so I just did an "emergency commit" to git, cleaned my local working copy using git clean -fdx and then reloaded the solution, rebuilt everything and the errors went away.
I'm loading FSharp.Data in the interactive console. The library is loaded without any problem:
> #r "FSharp.Data.dll";;
--> Referenced 'C:\Users\pw\AppData\Local\Temp\FSharp.Data.dll' (file may be locked by F# Interactive process)
> open FSharp.Data;;
However, when I'm trying to initialize CsvProvider (defined in FSharp.Data) I get the error message saying the type is not defined:
> type Stocks = CsvProvider<"C:\Users\pw\Downloads\msft.csv">;;
type Stocks = CsvProvider<"C:\Users\pw\Downloads\msft.csv">;;
--------------^^^^^^^^^^^
stdin(62,15): error FS0039: The type 'CsvProvider' is not defined
I thought the problem may be with file and assemblies paths but now I'm using absolute paths and the error remains. On the other hand, I am able to use the CsvProvider when I'm creating a standard, not interactive, project. Any help to make it work in interactive session highly appreciated.
The warning about file being locked looks worrisome. Can you copy FSharp.Data somewhere and reference it using absolute path:
\#r #"C:\Poligon\packages\FSharp.Data.2.1.0\lib\net40\FSharp.Data.dll";;
Downgrade your FSharp.Core to 4.7 and FSharp.Data to 3.3.3. It should work after that.
I am trying to compile jabber-net in Xamarin Studio so I can use it in a Xamarin.iOS app.
From other searches I have done I am told I need to recompile the source.
From command line I can build the dll, but I have no idea what version of .NET/Mono this is targeting.
This makes a jabber-net.dll and a jabber-net.dll.mdb.
If I add jabber-net.dll to my project, add the reqiured
using jabber.client;
...
...
...
JabberClient client = new JabberClient ();
and try to compile I am told.
/Users/brad/Projects/XMPPChat/XMPPChat/AppDelegate.cs(37,47): error CS0584: Internal compiler error: Could not import type jabber.client.JabberClient' fromjabber-net, Version=2.1.0.702, Culture=neutral, PublicKeyToken=924c5b18328d6f09'
/Users/brad/Projects/XMPPChat/XMPPChat/AppDelegate.cs(37,38): error CS0584: Internal compiler error: Could not import type jabber.client.JabberClient' fromjabber-net, Version=2.1.0.702, Culture=neutral, PublicKeyToken=924c5b18328d6f09'
/Users/brad/Projects/XMPPChat/XMPPChat/AppDelegate.cs(37,38): error CS0201: Only assignment, call, increment, decrement, and new object expressions can be used as a statement
I got no idea what is going on here...
When I try to open any of the .sln's (or include any of the existing projects, even the mono specific project) that came with jabber-net into my solution it will either hang trying to convert the project, or will tell me
The file '/Users/brad/Projects/XMPPChat/JabberNet-2.1.0.710/mono-jabber-net.csproj' could not be loaded.
and will spit out this error.
Any idea where to go from here? :|
Start a new solution from scratch, and add all of the .cs files except those in the test and examples directories. Also make sure you don't have an old version of the .dll around somewhere.