Compiling F# Sources

The Fsc task set in FAKE can be used to build F# source files and output libraries, modules, and executables by using the bundled FSharp.Compiler.Service. In this tutorial we will look at these compile tasks.

The Fsc task

The Fsc task can be used in standard FAKE targets:

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#r "/path/to/FakeLib.dll"
open Fake

Target "Otherthing.dll" (fun _ ->
    ["Otherthing.fs"; "Otherthing2.fs"]
    |> FscHelper.compile [
        FscHelper.Target FscHelper.TargetType.Library
    ]
    |> function 0 -> () | c -> failwithf "F# compiler return code: %i" c
)

Target "Main.exe" (fun _ ->
    ["Main.fs"]
    |> FscHelper.compile [
        FscHelper.References ["Something.dll"; "Otherthing.dll"]
    ]
    |> function 0 -> () | c -> failwithf "F# compiler return code: %i" c
)

The FscHelper.compile task takes two arguments:

1. a list of compile parameters (FscParam), and
2. a list of source files.

We start with the list of source files, and send it into the FscHelper.compile task using F#'s |> operator. The list of parameters included in the first argument will override the default parameters.

In the above examples, notice that we don't always override the output file name. By default FscHelper.compile will behave exactly the same way as fsc.exe. If you don't specify an output file: it will use the name of the first input file, and the appropriate filename extension.

FscParam.Target also behaves in the same way as the fsc.exe --target: switch: if you don't override it, it defaults to an executable output type.

You can override all fsc.exe default compile parameters by explicitly passing the values you want to use. All F# compiler parameters are available as FscParam union cases:

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Target "Something.dll" (fun _ ->
    ["Something.fs"]
    |> FscHelper.compile [
        FscHelper.Out "Something.dll"
        FscHelper.Target FscHelper.TargetType.Library
        FscHelper.NoOptimizationData
        FscHelper.Checked true
    ]
    |> function 0 -> () | c -> failwithf "F# compiler return code: %i" c
)

See the API docs for FscHelper for details of the available parameters.

The FscHelper.compile task will print any compile warnings or errors. If there's any compile error, it won't raise any error to interrupt the build process, instead, it returns the exit status of the compile process.

Having an exit status code returned can be useful when you're trying to integrate FAKE with other build management tools, e.g. your own CI server or a test runner.

FscHelper.compileFiles

This task is lower level than the previous one. It takes a list of source files and a list of strings which contains the same arguments you'd pass in to the fsc.exe command-line tool. It too prints warnings and errors, and returns a compile exit status code. E.g.:

Target "Something.dll" (fun _ -> ["Something.fs"] |> FscHelper.compileFiles ["-o"; "Something.dll"; "--target:library"] |> ignore )

This task may be useful when you already have compile options in string format and just need to pass them in to your build tool. You'd just need to split the string on whitespace, and pass the resulting list into FscHelper.compileFiles.