I'm trying to create some kind of interface, but i cannot find how to use custom attributes in F# as MSDN only shows usage of CLR attributes. This is what i want to achieve:
open System
type Command (name : string) =
inherit Attribute()
member this.Name = name
[<Command("something")>]
let doSomething () =
Console.Write("I'm doing something")
[<Command("somethingElse")>]
let doSomethingElse () =
Console.Write("I'm doing something else")
[<EntryPoint>]
let main args =
let command = Console.ReadLine()
// find function where Command.Name = command and call it
Console.Read()
0
To extend on your answer, a more generic approach would be to get all the types and then filter the functions that have the attribute you're looking for (as your approach would break down once your application grows and no longer has everything "packed" into the Program class):
let getCommands () =
let types = Assembly.GetExecutingAssembly().GetTypes()
let commands =
types
|> Array.collect (fun typ -> typ.GetMethods())
|> Array.choose (fun mi ->
mi.CustomAttributes
|> Seq.tryFind (fun attr -> attr.AttributeType = typeof<Command>)
|> Option.map (fun attr -> attr, mi))
let commandsMap =
commands
|> Seq.map (fun (attr, mi) ->
let name =
let arg = attr.ConstructorArguments.[0]
unbox<string> arg.Value
name, mi)
|> Map.ofSeq
commandsMap
This gets all the functions from all the types in the executing assembly, then filters out everything that doesn't have command attribute. Then it builds a map where the key is the attribute argument and the value is the MethodInfo of the function.
Ok, found it.
Reflection.Assembly.GetExecutingAssembly().GetType("Program").GetMethods()
Program typename is not viable in code so it cannot be used in typeof<Program>, but this type exists and can be taken from assembly.
Related
I'm trying to write an installer for my application that runs (mostly) a bunch of database migrations.
I have a very simple start here, I'm just trying to figure out what invokeMethod should equal.
let RunMigration (fsModule: System.Type) =
fsModule.GetProperties()
|> Array.filter (fun property -> property.Name = "run")
|> Array.map(fun property -> property |> invokeMethod ; "Ran successfully")
|> String.concat "<br/>"
let RunAllMigrations =
Assembly
.GetExecutingAssembly()
.GetTypes()
|> Array.filter FSharpType.IsModule
|> Array.filter (fun fsModule -> fsModule.Namespace = "DredgePos.Migrations")
|> Array.map RunMigration
|> String.concat "<br/><hr/>"
At the moment as you can see it is a fairly simple process of
Get all the types in the assembly
Getting all modules in the Migrations namespace.
Then if that module has a function named run, I want to invoke it.
How do I invoke it?
EDIT:
The run method will always be Unit -> Unit
let run () = ()
In your RunMigration method, you are getting a list of properties of the type - but a function declared as in your example should be compiled as a method. For example, if I have the following module in the current assembly:
module XX =
let run () = printfn "hello!"
It should be possible to invoke this if the RunMigration function first finds the run method and then calls the Invoke operation with no arguments (and null as the instance, since this is a static method):
let RunMigration (fsModule: System.Type) =
let mi = fsModule.GetMethod("run")
mi.Invoke(null,[||]) |> ignore
This returns obj value, which will be null (as the method returns unit) and so you can typically ignore the result.
I am trying to find let bindings with a specific attribute and type, throughout a given assembly.
For instance, the following type and attribute:
type TargetType = { somedata: string }
type MarkingAttribute() = inherit System.Attribute()
Then I would like to find the value in the following module:
module SomeModule =
[<Marking>]
let valueIWantToFind = {somedata = "yoyo"}
So what I am looking for is a function with the following signature (assuming it is suitable for a generic function signature):
let valuesOfTypeWithAttribute<'t,'attr> (assembly: Assembly) : 't list = ...
My futile attempts seem to be blocked by my lack of understanding how F# modules are translated to CLR (CLI?) classes.
I have the following FSI snippet which unfortunately finds nothing:
open System.Reflection
let types = Assembly.GetExecutingAssembly().GetTypes()
let fiWithAttribute (attributeType: System.Type) (fi: FieldInfo) =
fi.CustomAttributes
|> Seq.exists (fun attr -> attr.AttributeType = attributeType)
let fields =
types
|> Array.collect (fun t -> t.GetFields())
|> Array.filter (fiWithAttribute typeof<MarkingAttribute>)
Any help or pointers will be greatly appreciated.
Modules are compiled as classes with static members. Load your assembly into a value called assembly, and start to investigate:
> let publicTypes = assembly.GetExportedTypes ();;
val publicTypes : System.Type [] =
[|Ploeh.StackOverflow.Q36245870.TargetType;
Ploeh.StackOverflow.Q36245870.MarkingAttribute;
Ploeh.StackOverflow.Q36245870.SomeModule|]
As you can tell, SomeModule is one of those types:
> let someModule =
publicTypes |> Array.find (fun t -> t.Name.EndsWith "SomeModule");;
val someModule : System.Type = Ploeh.StackOverflow.Q36245870.SomeModule
You can now get all members of the type:
> let members = someModule.GetMembers ();;
val members : MemberInfo [] =
[|Ploeh.StackOverflow.Q36245870.TargetType get_valueIWantToFind();
System.String ToString(); Boolean Equals(System.Object);
Int32 GetHashCode(); System.Type GetType();
Ploeh.StackOverflow.Q36245870.TargetType valueIWantToFind|]
This array includes the let-bound function valueIWantToFind, and it has the desired attribute:
> let attrs = members.[5].GetCustomAttributes ();;
val attrs : System.Collections.Generic.IEnumerable<System.Attribute> =
[|Ploeh.StackOverflow.Q36245870.MarkingAttribute;
Microsoft.FSharp.Core.CompilationMappingAttribute|]
Mark's response led me onto the path of success. The reflection does not work for modules defined entirely in FSI (at least not for me in my setup).
The function I came up with looks like this:
open Microsoft.FSharp.Reflection
let letBindingsWithTypeAndAttribute<'t,'attr> (assembly: Assembly) : 't array =
let publicTypes = assembly.GetExportedTypes ()
let modules = publicTypes |> Array.filter FSharpType.IsModule
let members = modules |> Array.collect (fun m -> m.GetMembers ())
let miHasAttribute (mi : MemberInfo) =
mi.GetCustomAttributes ()
|> Seq.exists (fun attr' -> attr'.GetType() = typeof<'attr>)
let withAttr =
members
|> Array.filter miHasAttribute
let valueOfBinding (mi : MemberInfo) =
let property = mi.Name
mi.DeclaringType.GetProperty(property).GetValue null
withAttr
|> Array.map valueOfBinding
|> Array.choose (fun o -> match o with
| :? 't as x -> Some x
| _ -> None)
I'm having a bit of trouble with the following FSharp/F# code:
module File1
let api a =
printf ("VALUE = %A") a
let router ops =
[|
api (ops (fun (list, _) -> list()))
api (ops (fun (_, get) -> get 1))
|]
let withContext ops handler =
let context = "CONTEXT"
handler (ops context)
let operations context =
printf ("CONTEXT = %s") context
let list () = [|1;2;3|]
let get id = "Test"
(list, get)
let setup() =
let ops = withContext operations
router ops
Results in the following error
Results in the following compation error
Error 1 Type mismatch. Expecting a
((unit -> int []) * (int -> int []) -> int []) -> 'a
but given a
((unit -> int []) * (int -> string) -> 'b) -> 'b
The type 'int []' does not match the type 'string'
I know the problem is that ops function has been bound to return a int[] but I want to be able to also return a string.
I think I'm missing a trick with some generic declarations but after hours of moving code around I can’t seem to work it out.
(I've simplified the code to highlight my problem)
The error is because ops needs to have a return type of its handler resolved at compilation, and you want to return different types base on some run-time logic.
It is basically an equivalent of:
let fun1 switch arg2 arg3 =
if switch then
arg2
else
arg3
and you want to run it this way:
fun1 true 1 "string"
Of course, arg2 and arg3 need to have the same type, so it won't work
What you can do is to run "api" function on a handler result, before returning it (so it will always the same type - unit).
let router ops =
[|
ops (fun (list, _) -> api <| list()))
ops (fun (_, get) -> api <| get 1))
|]
Alternatively, you could return objects of discriminated union type (then you will need some more logic in api function).
(Technically, you could also return obj).
Bonus
You don't need the array of units to be returned in a router function, returning one unit is just fine:
let router ops =
ops (fun (list, _) -> api <| list()))
ops (fun (_, get) -> api <| get 1))
In this way, setup function will also return unit and you will be able to run it without a need to run ignore on the result to get rid of This expression should have type 'unit', but has type 'unit[]' warning.
Your code is hard for me to understand, but I think the basic issue is that you want withContext to have a "rank 2" type (so that the universal quantification of the type variable 'b can happen after the application of the first argument). In F#, this can be accomplished by creating a new type with a generic method and using that:
let api a =
printf ("VALUE = %A") a
type Handler<'a> = abstract Handle<'b> : f:('a->'b) -> 'b
let router (ops:Handler<_>) =
[|
api (ops.Handle (fun (list, _) -> list()))
api (ops.Handle (fun (_, get) -> get 1))
|]
let withContext ops =
let context = "CONTEXT"
{ new Handler<_> with member __.Handle f = f (ops context) }
let operations context =
printf ("CONTEXT = %s") context
let list () = [|1;2;3|]
let get id = "Test"
(list, get)
let setup() =
let ops = withContext operations
router ops
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.
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"
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.
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
Recently I attended a tutorial by Keith Battochi on type providers, in which he introduced a variant of the MiniCsv type provider in the MSDN tutorial. Unfortunately, my laptop wasn't available, so I had to write down the code by hand as well as I could. I believe I've recreated the type provider, but I'm getting
error FS3033: The type provider 'CsvFileTypeProvider+CsvFileTypeProvider' reported an error: container type for 'CsvFileProvider.Row' was already set to 'CsvFileProvider.CsvFile,Filename="events.csv"
When I look at the code, I can't see how I'm adding the Row type to the container twice (or to some other container). Removing selected lines of the code doesn't help.
Here's how I'm calling the code in fsi:
#r "CsvFileTypeProvider.dll"
open CsvFileProvider
let eventInfos = new CsvFile<"events.csv">() ;;
And here's the code itself:
module CsvFileTypeProvider
open Samples.FSharp.ProvidedTypes
open Microsoft.FSharp.Core.CompilerServices
let getType str =
if System.DateTime.TryParse(str, ref Unchecked.defaultof<_>) then
typeof<System.DateTime>, (fun (str:Quotations.Expr) -> <## System.DateTime.Parse(%%str) ##>)
elif System.Int32.TryParse(str, ref Unchecked.defaultof<_>) then
typeof<System.Int32>, (fun (str:Quotations.Expr) -> <## System.Int32.Parse(%%str) ##>)
elif System.Double.TryParse(str, ref Unchecked.defaultof<_>) then
typeof<System.Double>, (fun (str:Quotations.Expr) -> <## System.Double.Parse(%%str) ##>)
else
typeof<string>, (fun (str:Quotations.Expr) -> <## %%str ##>)
[<TypeProvider>]
type CsvFileTypeProvider() =
inherit TypeProviderForNamespaces()
let asm = typeof<CsvFileTypeProvider>.Assembly
let ns = "CsvFileProvider"
let csvFileProviderType = ProvidedTypeDefinition(asm, ns, "CsvFile", None)
let parameters = [ProvidedStaticParameter("Filename", typeof<string>)]
do csvFileProviderType.DefineStaticParameters(parameters, fun tyName [| :? string as filename |] ->
let rowType = ProvidedTypeDefinition(asm, ns, "Row", Some(typeof<string[]>))
let lines = System.IO.File.ReadLines(filename) |> Seq.map (fun line -> line.Split(','))
let columnNames = lines |> Seq.nth 0
let resultTypes = lines |> Seq.nth 1 |> Array.map getType
for idx in 0 .. (columnNames.Length - 1) do
let col = columnNames.[idx]
let ty, converter = resultTypes.[idx]
let prop = ProvidedProperty(col, ty)
prop.GetterCode <- fun [row] -> converter <## (%%row:string[]).[idx] ##>
rowType.AddMember(prop)
let wholeFileType = ProvidedTypeDefinition(asm, ns, tyName, Some(typedefof<seq<_>>.MakeGenericType(rowType)))
wholeFileType.AddMember(rowType)
let ctor = ProvidedConstructor(parameters = []) // the *type* is parameterized but the *constructor* gets no args
ctor.InvokeCode <- //given the inputs, what will we get as the outputs? Now we want to read the *data*, skip the header
fun [] -> <## System.IO.File.ReadLines(filename) |> Seq.skip 1 |> Seq.map (fun line -> line.Split(',')) ##>
wholeFileType.AddMember(ctor)
wholeFileType
)
do base.AddNamespace(ns, [csvFileProviderType])
[<TypeProviderAssembly>]
do()
Thanks for any help!
you need to use another constructor when defining 'Row' type. Existing ProvidedTypeDefinition type exposes two constructors:
(assembly, namespace, typename, base type) - defines top level type whose container is namespace.
(typename, basetype) - defines nested type that should be added to some another type.
Now Row type is defined using first constructor so it is treated as top level type. Exception is raised when this type is later added to wholeFileType as nested.