Why are some functions available only in F# script files, not in source files?

Question

I have noticed this a few times now. An example of an offending function is Array.take. In a script file I can write

[|1; 2; 4; 7; 6; 5|]
|> Array.take 3
|> Array.iter (printfn "%d")

and this works without a problem. But if I try to use Array.take in an actual source file, I get the following error

[|1; 2; 4; 7; 6; 5|]
|> Array.take 3 // RED SQUIGGLY ERROR HERE
|> Array.iter (printfn "%d")

and the error message is:

The value, constructor, namespace or type 'take' is not defined

So, what gives? Thanks in advance for your help.

TheInnerLight · Accepted Answer · 2015-12-26 23:13:41Z

4

I suspect that you're seeing this is due to different versions of F#. There was an attempt to regularise a lot of the List Seq and Array functions in F# 4.0, see: https://visualfsharp.codeplex.com/wikipage?title=Status

One of the functions that was added as part of that process was Array.take.

In F# interactive, no doubt you are using the latest version of F# but presumably you are not in your compiled project.

This could be because you haven't changed the version in the project settings or it could be because you have a nuget package attached your project which references a specific version of F# Core via nuget.

If you go to your project properties, you should see an a 'Target F# Runtime' setting, change this to F# 4.0. If I remember correctly, a nuget reference to a specific F# Core version will prevent you from changing that setting, in which case you'll need to delete the reference to F# core and re-add the correct version as a reference from the list of assemblies.

edited Dec 26, 2015 at 23:13

answered Dec 26, 2015 at 23:08

TheInnerLight

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2 Comments

Shredderroy Over a year ago

the Target F# Runtime is set to 4.3.0.0 and is greyed out. The project is using version 4.3.0.0 of FSharp.Core. In spite of that, I encounter the problem.

TheInnerLight Over a year ago

@Shredderroy F# Core 4.3.0.0 corresponds to F# 3.0. F# 4.0 uses F# Core version 4.4.0.0. Delete the reference to F# Core and re-add it from the list of Extensions assemblies.

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