Extracting meta data from nupkg file with F# looks like C# Linq

Question

The code snippet below examines a nuget package file (zip file with meta) and extracts all file names referenced inside. The final result should be a Set<string> with all file names. My problem is that the code looks like a nested Linq query in c# and the usage of Seq.iter blocks me to build the Set collection. Can you please give me some kind of advice how to improve the F# code? Am I missing some fundamental concept?

getDependencies nugetPackagesFile
                |> Seq.iter(fun (name,ver) ->
                    name + "." + ver
                    |> fun pkgName ->
                        !! ("./src/packages/*/" + pkgName + ".nupkg")
                        |> Seq.iter(fun pkg ->
                            global.NuGet.ZipPackage(pkg).GetFiles()
                            |> Seq.iter(fun file -> filename file.Path |> printfn "%s")))

Current output:

Elders.Cronus.dll
Elders.Cronus.pdb
Elders.Cronus.DomainModeling.dll
Elders.Cronus.DomainModeling.pdb
log4net.dll
log4net.xml
log4net.dll
log4net.xml
log4net.dll
log4net.xml
log4net.dll
log4net.xml
log4net.dll
log4net.xml
log4net.dll
log4net.xml
log4net.dll
log4net.xml
Elders.Multithreading.Scheduler.dll
Elders.Multithreading.Scheduler.pdb
protobuf-net.dll
protobuf-net.pdb
protobuf-net.xml
protobuf-net.dll
protobuf-net.pdb
protobuf-net.xml
protobuf-net.dll
protobuf-net.pdb
protobuf-net.xml

Answer 1

Without being able to actually test (I can only guess what getDependencies, nugetPackagesFile, !! and filename are), something along the following should produce your desired set of dependencies:

getDependencies nugetPackagesFile
|> Seq.collect (fun (name, ver) -> 
       !! (sprintf "./src/packages/*/%s.%s.nupkg" name ver)
       |> Seq.collect (fun pkg -> NuGet.ZipPackage(pkg).GetFiles())
       |> Seq.map (fun f -> filename f.Path))
|> Set.ofSeq

or, depending on your taste (kind of DFS vs. BFS)

getDependencies nugetPackagesFile
|> Seq.collect (fun (name, ver) -> !! (sprintf "./src/packages/*/%s.%s.nupkg" name ver))
|> Seq.collect (fun pkg -> NuGet.ZipPackage(pkg).GetFiles())
|> Seq.map (fun f -> filename f.Path)
|> Set.ofSeq

where Seq.collect and map correspond to IEnumerable.SelectMany respectively Select in C#

Answer 2

Your code is very much imperative. I think this reads better:

for name, ver in getDependencies nugetPackagesFile do
    let pkgName = name + "." + ver
    for pkg in !! ("./src/packages/*/" + pkgName + ".nupkg") do
        for file in global.NuGet.ZipPackage(pkg).GetFiles() do
            filename file.Path |> printfn "%s"