Is there a way to import (open) specific functions in F#?

Question

Instead of importing a whole module, is there a way to open specific functions in another module? Something like:

open TestFuncs with [myTestFuncInOtherModule]

Answer 1

As you can see in the docs, the open keyword doesn't actually load a module or namespace. It just allows you to refer to elements in that module/namespace without refering to their fully qualified name.

Being so, when you use open you're just making it easier to call the functions in that module, not actually importing/loading them in memory, so the short answer for this question is that using the open keyword you can't do this to only one function.

You can achieve the same thing easily with a let binding, though:

let f = TestFuncs.myTestFuncInOtherModule

Answer 2

It's not currently possible, but I've actually put in a request for this to be added to the language. If you want to see this added in F# 4.0, one thing you could do is go vote for that request.

Another good workaround, that hasn't been mentioned yet by other answers, is to "pseudo-open" modules: assign a short name to modules whose contents you want to use. Like so:

module TP = Microsoft.FSharp.Data.TypeProviders
type mySchema = TP.SqlDataConnection<"...">
let db = mySchema.GetDataContext()

This gives you the convenience of not having to type the whole module name every time you want to reference its contents, but you maintain control of your namespace: this way there's no chance of accidental name collisions when you update a module to a new version and it adds new names.

Answer 3

You can refer to particular functions in another module using full function name ModuleName.funcName:

module One =
    let square x = x * x

module Two =
    let anothersquare x = One.square x