Can I call a function by name in f#? - f#

Question

Is there any way to call a function by name in F#? Given a string, I want to pluck a function value from the global namespace (or, in general, a given module), and call it. I know the type of the function already.
Why would I want to do this? I'm trying to work around fsi not having an --eval option. I have a script file that defines many int->() functions, and I want to execute one of them. Like so:
fsianycpu --use:script_with_many_funcs.fsx --eval "analyzeDataSet 1"
My thought was to write a trampoline script, like:
fsianycpu --use:script_with_many_funcs.fsx trampoline.fsx analyzeDataSet 1
In order to write "trampoline.fsx", I'd need to look up the function by name.

Answer 1

There is no built-in function for this, but you can implement it using .NET reflection. The idea is to search through all types available in the current assembly (this is where the current code is compiled) and dynamically invoke the method with the matching name. If you had this in a module, you'd have to check the type name too.
// Some sample functions that we might want to call
let hello() =
printfn "Hello world"
let bye() =
printfn "Bye"
// Loader script that calls function by name
open System
open System.Reflection
let callFunction name =
let asm = Assembly.GetExecutingAssembly()
for t in asm.GetTypes() do
for m in t.GetMethods() do
if m.IsStatic && m.Name = name then
m.Invoke(null, [||]) |> ignore
// Use the first command line argument (after -- in the fsi call below)
callFunction fsi.CommandLineArgs.[1]
This runs hello world when called by:
fsi --use:C:\temp\test.fsx --exec -- "hello"

Answer 2

You can use reflection to get the functions as MethodInfo's by FSharp function name
open System
open System.Reflection
let rec fsharpName (mi:MemberInfo) =
if mi.DeclaringType.IsNestedPublic then
sprintf "%s.%s" (fsharpName mi.DeclaringType) mi.Name
else
mi.Name
let functionsByName =
Assembly.GetExecutingAssembly().GetTypes()
|> Seq.filter (fun t -> t.IsPublic || t.IsNestedPublic)
|> Seq.collect (fun t -> t.GetMethods(BindingFlags.Static ||| BindingFlags.Public))
|> Seq.filter (fun m -> not m.IsSpecialName)
|> Seq.groupBy (fun m -> fsharpName m)
|> Map.ofSeq
|> Map.map (fun k v -> Seq.exactlyOne v)
You can then invoke the MethodInfo
functionsByName.[fsharpFunctionNameString].Invoke(null, objectArrayOfArguments)
But you probably need to do more work to parse your string arguments using the MethodInfo.GetParameters() types as a hint.

Answer 3

You could also use FSharp.Compiler.Service to make your own fsi.exe with an eval flag
open System
open Microsoft.FSharp.Compiler.Interactive.Shell
open System.Text.RegularExpressions
[<EntryPoint>]
let main(argv) =
let argAll = Array.append [| "C:\\fsi.exe" |] argv
let argFix = argAll |> Array.map (fun a -> if a.StartsWith("--eval:") then "--noninteractive" else a)
let optFind = argv |> Seq.tryFind (fun a -> a.StartsWith "--eval:")
let evalData = if optFind.IsSome then
optFind.Value.Replace("--eval:",String.Empty)
else
String.Empty
let fsiConfig = FsiEvaluationSession.GetDefaultConfiguration()
let fsiSession = FsiEvaluationSession(fsiConfig, argFix, Console.In, Console.Out, Console.Error)
if String.IsNullOrWhiteSpace(evalData) then
fsiSession.Run()
else
fsiSession.EvalInteraction(evalData)
0
If the above was compiled into fsieval.exe it could be used as so
fsieval.exe --load:script_with_many_funcs.fsx --eval:analyzeDataSet` 1