Compiler Services: Processing typed expression tree

This tutorial demonstrates how to get the checked, typed expressions tree (TAST) for F# code and how to walk over the tree.

This can be used for creating tools such as source code analyzers and refactoring tools. You can also combine the information with the API available from symbols.

NOTE: The FSharp.Compiler.Service API is subject to change when later versions of the nuget package are published

Getting checked expressions

To access the type-checked, resolved expressions, you need to create an instance of InteractiveChecker.

To use the interactive checker, reference FSharp.Compiler.Service.dll and open the relevant namespaces:

#r "FSharp.Compiler.Service.dll"
open System
open System.IO
open FSharp.Compiler.CodeAnalysis
open FSharp.Compiler.EditorServices
open FSharp.Compiler.Symbols
open FSharp.Compiler.Text

Checking code

We first parse and check some code as in the symbols tutorial. One difference is that we set keepAssemblyContents to true.

// Create an interactive checker instance 
let checker = FSharpChecker.Create(keepAssemblyContents=true)

let parseAndCheckSingleFile (input) = 
    let file = Path.ChangeExtension(System.IO.Path.GetTempFileName(), "fsx")  
    File.WriteAllText(file, input)
    // Get context representing a stand-alone (script) file
    let projOptions, _errors = 
        checker.GetProjectOptionsFromScript(file, SourceText.ofString input, assumeDotNetFramework=false)
        |> Async.RunSynchronously

    checker.ParseAndCheckProject(projOptions) 
    |> Async.RunSynchronously

Getting the expressions

After type checking a file, you can access the declarations and contents of the assembly, including expressions:

let input2 = 
      """
module MyLibrary 

open System

let foo(x, y) = 
    let msg = String.Concat("Hello", " ", "world")
    if msg.Length > 10 then 
        10 
    else 
        20

type MyClass() = 
    member x.MyMethod() = 1
      """
let checkProjectResults = 
    parseAndCheckSingleFile(input2)

checkProjectResults.Diagnostics // should be empty

Checked assemblies are made up of a series of checked implementation files. The "file" granularity matters in F# because initialization actions are triggered at the granularity of files. In this case there is only one implementation file in the project:

let checkedFile = checkProjectResults.AssemblyContents.ImplementationFiles.[0]

let rec printDecl prefix d = 
    match d with 
    | FSharpImplementationFileDeclaration.Entity (e, subDecls) -> 
        printfn "%sEntity %s was declared and contains %d sub-declarations" prefix e.CompiledName subDecls.Length
        for subDecl in subDecls do 
            printDecl (prefix+"    ") subDecl
    | FSharpImplementationFileDeclaration.MemberOrFunctionOrValue(v, vs, e) -> 
        printfn "%sMember or value %s was declared" prefix  v.CompiledName
    | FSharpImplementationFileDeclaration.InitAction(e) -> 
        printfn "%sA top-level expression was declared" prefix 


for d in checkedFile.Declarations do 
   printDecl "" d

// Entity MyLibrary was declared and contains 4 sub-declarations
//     Member or value foo was declared
//     Entity MyClass was declared and contains 0 sub-declarations
//     Member or value .ctor was declared
//     Member or value MyMethod was declared

As can be seen, the only declaration in the implementation file is that of the module MyLibrary, which contains fours sub-declarations.

As an aside, one peculiarity here is that the member declarations (e.g. the "MyMethod" member) are returned as part of the containing module entity, not as part of their class. Note that the class constructor is returned as a separate declaration. The class type definition has been "split" into a constructor and the other declarations.

let myLibraryEntity, myLibraryDecls =    
   match checkedFile.Declarations.[0] with 
   | FSharpImplementationFileDeclaration.Entity (e, subDecls) -> (e, subDecls)
   | _ -> failwith "unexpected"

What about the expressions, for example the body of function "foo"? Let's find it:

let (fooSymbol, fooArgs, fooExpression) = 
    match myLibraryDecls.[0] with 
    | FSharpImplementationFileDeclaration.MemberOrFunctionOrValue(v, vs, e) -> (v, vs, e)
    | _ -> failwith "unexpected"

Here 'fooSymbol' is a symbol associated with the declaration of 'foo', 'fooArgs' represents the formal arguments to the 'foo' function, and 'fooExpression' is an expression for the implementation of the 'foo' function.

Once you have an expression, you can work with it much like an F# quotation. For example, you can find its declaration range and its type:

fooExpression.Type  // shows that the return type of the body expression is 'int'
fooExpression.Range  // shows the declaration range of the expression implementing 'foo'

Walking over expressions

Expressions are analyzed using active patterns, much like F# quotations. Here is a generic expression visitor:

let rec visitExpr f (e:FSharpExpr) = 
    f e
    match e with 
    | FSharpExprPatterns.AddressOf(lvalueExpr) -> 
        visitExpr f lvalueExpr
    | FSharpExprPatterns.AddressSet(lvalueExpr, rvalueExpr) -> 
        visitExpr f lvalueExpr; visitExpr f rvalueExpr
    | FSharpExprPatterns.Application(funcExpr, typeArgs, argExprs) -> 
        visitExpr f funcExpr; visitExprs f argExprs
    | FSharpExprPatterns.Call(objExprOpt, memberOrFunc, typeArgs1, typeArgs2, argExprs) -> 
        visitObjArg f objExprOpt; visitExprs f argExprs
    | FSharpExprPatterns.Coerce(targetType, inpExpr) -> 
        visitExpr f inpExpr
    | FSharpExprPatterns.FastIntegerForLoop(startExpr, limitExpr, consumeExpr, isUp, _, _) -> 
        visitExpr f startExpr; visitExpr f limitExpr; visitExpr f consumeExpr
    | FSharpExprPatterns.ILAsm(asmCode, typeArgs, argExprs) -> 
        visitExprs f argExprs
    | FSharpExprPatterns.ILFieldGet (objExprOpt, fieldType, fieldName) -> 
        visitObjArg f objExprOpt
    | FSharpExprPatterns.ILFieldSet (objExprOpt, fieldType, fieldName, valueExpr) -> 
        visitObjArg f objExprOpt
    | FSharpExprPatterns.IfThenElse (guardExpr, thenExpr, elseExpr) -> 
        visitExpr f guardExpr; visitExpr f thenExpr; visitExpr f elseExpr
    | FSharpExprPatterns.Lambda(lambdaVar, bodyExpr) -> 
        visitExpr f bodyExpr
    | FSharpExprPatterns.Let((bindingVar, bindingExpr, dbg), bodyExpr) -> 
        visitExpr f bindingExpr; visitExpr f bodyExpr
    | FSharpExprPatterns.LetRec(recursiveBindings, bodyExpr) ->
        for _,bindingExpr,_ in recursiveBindings do visitExpr f bindingExpr
        visitExpr f bodyExpr
    | FSharpExprPatterns.NewArray(arrayType, argExprs) -> 
        visitExprs f argExprs
    | FSharpExprPatterns.NewDelegate(delegateType, delegateBodyExpr) -> 
        visitExpr f delegateBodyExpr
    | FSharpExprPatterns.NewObject(objType, typeArgs, argExprs) -> 
        visitExprs f argExprs
    | FSharpExprPatterns.NewRecord(recordType, argExprs) ->  
        visitExprs f argExprs
    | FSharpExprPatterns.NewAnonRecord(recordType, argExprs) ->  
        visitExprs f argExprs
    | FSharpExprPatterns.NewTuple(tupleType, argExprs) -> 
        visitExprs f argExprs
    | FSharpExprPatterns.NewUnionCase(unionType, unionCase, argExprs) -> 
        visitExprs f argExprs
    | FSharpExprPatterns.Quote(quotedExpr) -> 
        visitExpr f quotedExpr
    | FSharpExprPatterns.FSharpFieldGet(objExprOpt, recordOrClassType, fieldInfo) -> 
        visitObjArg f objExprOpt
    | FSharpExprPatterns.AnonRecordGet(objExpr, recordOrClassType, fieldInfo) -> 
        visitExpr f objExpr
    | FSharpExprPatterns.FSharpFieldSet(objExprOpt, recordOrClassType, fieldInfo, argExpr) -> 
        visitObjArg f objExprOpt; visitExpr f argExpr
    | FSharpExprPatterns.Sequential(firstExpr, secondExpr) -> 
        visitExpr f firstExpr; visitExpr f secondExpr
    | FSharpExprPatterns.TryFinally(bodyExpr, finalizeExpr, dbgTry, dbgFinally) -> 
        visitExpr f bodyExpr; visitExpr f finalizeExpr
    | FSharpExprPatterns.TryWith(bodyExpr, _, _, catchVar, catchExpr, dbgTry, dbgWith) -> 
        visitExpr f bodyExpr; visitExpr f catchExpr
    | FSharpExprPatterns.TupleGet(tupleType, tupleElemIndex, tupleExpr) -> 
        visitExpr f tupleExpr
    | FSharpExprPatterns.DecisionTree(decisionExpr, decisionTargets) -> 
        visitExpr f decisionExpr; List.iter (snd >> visitExpr f) decisionTargets
    | FSharpExprPatterns.DecisionTreeSuccess (decisionTargetIdx, decisionTargetExprs) -> 
        visitExprs f decisionTargetExprs
    | FSharpExprPatterns.TypeLambda(genericParam, bodyExpr) -> 
        visitExpr f bodyExpr
    | FSharpExprPatterns.TypeTest(ty, inpExpr) -> 
        visitExpr f inpExpr
    | FSharpExprPatterns.UnionCaseSet(unionExpr, unionType, unionCase, unionCaseField, valueExpr) -> 
        visitExpr f unionExpr; visitExpr f valueExpr
    | FSharpExprPatterns.UnionCaseGet(unionExpr, unionType, unionCase, unionCaseField) -> 
        visitExpr f unionExpr
    | FSharpExprPatterns.UnionCaseTest(unionExpr, unionType, unionCase) -> 
        visitExpr f unionExpr
    | FSharpExprPatterns.UnionCaseTag(unionExpr, unionType) -> 
        visitExpr f unionExpr
    | FSharpExprPatterns.ObjectExpr(objType, baseCallExpr, overrides, interfaceImplementations) -> 
        visitExpr f baseCallExpr
        List.iter (visitObjMember f) overrides
        List.iter (snd >> List.iter (visitObjMember f)) interfaceImplementations
    | FSharpExprPatterns.TraitCall(sourceTypes, traitName, typeArgs, typeInstantiation, argTypes, argExprs) -> 
        visitExprs f argExprs
    | FSharpExprPatterns.ValueSet(valToSet, valueExpr) -> 
        visitExpr f valueExpr
    | FSharpExprPatterns.WhileLoop(guardExpr, bodyExpr, dbg) -> 
        visitExpr f guardExpr; visitExpr f bodyExpr
    | FSharpExprPatterns.BaseValue baseType -> ()
    | FSharpExprPatterns.DefaultValue defaultType -> ()
    | FSharpExprPatterns.ThisValue thisType -> ()
    | FSharpExprPatterns.Const(constValueObj, constType) -> ()
    | FSharpExprPatterns.Value(valueToGet) -> ()
    | _ -> failwith (sprintf "unrecognized %+A" e)

and visitExprs f exprs = 
    List.iter (visitExpr f) exprs

and visitObjArg f objOpt = 
    Option.iter (visitExpr f) objOpt

and visitObjMember f memb = 
    visitExpr f memb.Body

Let's use this expression walker:

fooExpression |> visitExpr (fun e -> printfn "Visiting %A" e)

// Prints:
//
// Visiting Let...
// Visiting Call...
// Visiting Const ("Hello", ...)
// Visiting Const (" ", ...)
// Visiting Const ("world", ...)
// Visiting IfThenElse...
// Visiting Call...
// Visiting Call...
// Visiting Value ...
// Visiting Const ...
// Visiting Const ...
// Visiting Const ...

Note that

The visitExpr function is recursive (for nested expressions).
Pattern matching is removed from the tree, into a form called 'decision trees'.

Summary

In this tutorial, we looked at the basics of working with checked declarations and expressions.

In practice, it is also useful to combine the information here with some information you can obtain from the symbols tutorial.

namespace System

namespace System.IO

Multiple items
namespace FSharp

--------------------
namespace Microsoft.FSharp

namespace FSharp.Compiler

namespace FSharp.Compiler.CodeAnalysis

namespace FSharp.Compiler.EditorServices

namespace FSharp.Compiler.Symbols

Multiple items
namespace FSharp

--------------------
namespace Microsoft.FSharp

--------------------
type FSharpAttribute = member Format: context: FSharpDisplayContext -> string member IsAttribute: unit -> bool member AttributeType: FSharpEntity with get member ConstructorArguments: IList<FSharpType * obj> with get member IsUnresolved: bool with get member NamedArguments: IList<FSharpType * string * bool * obj> with get member Range: range with get
<summary> Represents a custom attribute attached to F# source code or a compiler .NET component </summary>

namespace FSharp.Compiler.Text

val checker: FSharpChecker

type FSharpChecker = member CheckFileInProject: parseResults: FSharpParseFileResults * fileName: string * fileVersion: int * sourceText: ISourceText * options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpCheckFileAnswer> member ClearCache: options: FSharpProjectOptions seq * ?userOpName: string -> unit + 1 overload member ClearLanguageServiceRootCachesAndCollectAndFinalizeAllTransients: unit -> unit member Compile: argv: string array * ?userOpName: string -> Async<FSharpDiagnostic array * exn option> member FindBackgroundReferencesInFile: fileName: string * options: FSharpProjectOptions * symbol: FSharpSymbol * ?canInvalidateProject: bool * [<Experimental ("This FCS API is experimental and subject to change.")>] ?fastCheck: bool * ?userOpName: string -> Async<range seq> + 1 overload member GetBackgroundCheckResultsForFileInProject: fileName: string * options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpParseFileResults * FSharpCheckFileResults> member GetBackgroundParseResultsForFileInProject: fileName: string * options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpParseFileResults> member GetBackgroundSemanticClassificationForFile: fileName: string * options: FSharpProjectOptions * ?userOpName: string -> Async<SemanticClassificationView option> + 1 overload member GetParsingOptionsFromCommandLineArgs: sourceFiles: string list * argv: string list * ?isInteractive: bool * ?isEditing: bool -> FSharpParsingOptions * FSharpDiagnostic list + 1 overload member GetParsingOptionsFromProjectOptions: options: FSharpProjectOptions -> FSharpParsingOptions * FSharpDiagnostic list ...
<summary> Used to parse and check F# source code. </summary>

static member FSharpChecker.Create: ?projectCacheSize: int * ?keepAssemblyContents: bool * ?keepAllBackgroundResolutions: bool * ?legacyReferenceResolver: LegacyReferenceResolver * ?tryGetMetadataSnapshot: FSharp.Compiler.AbstractIL.ILBinaryReader.ILReaderTryGetMetadataSnapshot * ?suggestNamesForErrors: bool * ?keepAllBackgroundSymbolUses: bool * ?enableBackgroundItemKeyStoreAndSemanticClassification: bool * ?enablePartialTypeChecking: bool * ?parallelReferenceResolution: bool * ?captureIdentifiersWhenParsing: bool * [<Experimental ("This parameter is experimental and likely to be removed in the future.")>] ?documentSource: DocumentSource * [<Experimental ("This parameter is experimental and likely to be removed in the future.")>] ?useTransparentCompiler: bool -> FSharpChecker

val parseAndCheckSingleFile: input: string -> FSharpCheckProjectResults

val input: string

val file: string

type Path = static member ChangeExtension: path: string * extension: string -> string static member Combine: path1: string * path2: string -> string + 4 overloads static member EndsInDirectorySeparator: path: ReadOnlySpan<char> -> bool + 1 overload static member Exists: path: string -> bool static member GetDirectoryName: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetExtension: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFileName: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFileNameWithoutExtension: path: ReadOnlySpan<char> -> ReadOnlySpan<char> + 1 overload static member GetFullPath: path: string -> string + 1 overload static member GetInvalidFileNameChars: unit -> char array ...
<summary>Performs operations on <see cref="T:System.String" /> instances that contain file or directory path information. These operations are performed in a cross-platform manner.</summary>

[<return:NotNullIfNotNullAttribute ("path")>] Path.ChangeExtension(path: string, extension: string) : string

Path.GetTempFileName() : string

type File = static member AppendAllBytes: path: string * bytes: byte array -> unit + 1 overload static member AppendAllBytesAsync: path: string * bytes: byte array * ?cancellationToken: CancellationToken -> Task + 1 overload static member AppendAllLines: path: string * contents: IEnumerable<string> -> unit + 1 overload static member AppendAllLinesAsync: path: string * contents: IEnumerable<string> * encoding: Encoding * ?cancellationToken: CancellationToken -> Task + 1 overload static member AppendAllText: path: string * contents: string -> unit + 3 overloads static member AppendAllTextAsync: path: string * contents: string * encoding: Encoding * ?cancellationToken: CancellationToken -> Task + 3 overloads static member AppendText: path: string -> StreamWriter static member Copy: sourceFileName: string * destFileName: string -> unit + 1 overload static member Create: path: string -> FileStream + 2 overloads static member CreateSymbolicLink: path: string * pathToTarget: string -> FileSystemInfo ...
<summary>Provides static methods for the creation, copying, deletion, moving, and opening of a single file, and aids in the creation of <see cref="T:System.IO.FileStream" /> objects.</summary>

File.WriteAllText(path: string, contents: ReadOnlySpan<char>) : unit
File.WriteAllText(path: string, contents: string) : unit
File.WriteAllText(path: string, contents: ReadOnlySpan<char>, encoding: Text.Encoding) : unit
File.WriteAllText(path: string, contents: string, encoding: Text.Encoding) : unit

val projOptions: FSharpProjectOptions

val _errors: FSharp.Compiler.Diagnostics.FSharpDiagnostic list

member FSharpChecker.GetProjectOptionsFromScript: fileName: string * source: ISourceText * ?previewEnabled: bool * ?loadedTimeStamp: DateTime * ?otherFlags: string array * ?useFsiAuxLib: bool * ?useSdkRefs: bool * ?assumeDotNetFramework: bool * ?sdkDirOverride: string * ?optionsStamp: int64 * ?userOpName: string -> Async<FSharpProjectOptions * FSharp.Compiler.Diagnostics.FSharpDiagnostic list>

module SourceText from FSharp.Compiler.Text
<summary> Functions related to ISourceText objects </summary>

val ofString: string -> ISourceText
<summary> Creates an ISourceText object from the given string </summary>

Multiple items
type Async = static member AsBeginEnd: computation: ('Arg -> Async<'T>) -> ('Arg * AsyncCallback * objnull -> IAsyncResult) * (IAsyncResult -> 'T) * (IAsyncResult -> unit) static member AwaitEvent: event: IEvent<'Del,'T> * ?cancelAction: (unit -> unit) -> Async<'T> (requires delegate and 'Del :> Delegate) static member AwaitIAsyncResult: iar: IAsyncResult * ?millisecondsTimeout: int -> Async<bool> static member AwaitTask: task: Task<'T> -> Async<'T> + 1 overload static member AwaitWaitHandle: waitHandle: WaitHandle * ?millisecondsTimeout: int -> Async<bool> static member CancelDefaultToken: unit -> unit static member Catch: computation: Async<'T> -> Async<Choice<'T,exn>> static member Choice: computations: Async<'T option> seq -> Async<'T option> static member FromBeginEnd: beginAction: (AsyncCallback * objnull -> IAsyncResult) * endAction: (IAsyncResult -> 'T) * ?cancelAction: (unit -> unit) -> Async<'T> + 3 overloads static member FromContinuations: callback: (('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) -> unit) -> Async<'T> ...

--------------------
type Async<'T>

static member Async.RunSynchronously: computation: Async<'T> * ?timeout: int * ?cancellationToken: Threading.CancellationToken -> 'T

member FSharpChecker.ParseAndCheckProject: projectSnapshot: FSharpProjectSnapshot * ?userOpName: string -> Async<FSharpCheckProjectResults>
member FSharpChecker.ParseAndCheckProject: options: FSharpProjectOptions * ?userOpName: string -> Async<FSharpCheckProjectResults>

val input2: string

val checkProjectResults: FSharpCheckProjectResults

property FSharpCheckProjectResults.Diagnostics: FSharp.Compiler.Diagnostics.FSharpDiagnostic array with get
<summary> The errors returned by processing the project </summary>

val checkedFile: FSharpImplementationFileContents

property FSharpCheckProjectResults.AssemblyContents: FSharpAssemblyContents with get
<summary> Get a view of the overall contents of the assembly. Only valid to use if HasCriticalErrors is false. </summary>

property FSharpAssemblyContents.ImplementationFiles: FSharpImplementationFileContents list with get
<summary> The contents of the implementation files in the assembly </summary>

val printDecl: prefix: string -> d: FSharpImplementationFileDeclaration -> unit

val prefix: string

val d: FSharpImplementationFileDeclaration

type FSharpImplementationFileDeclaration = | Entity of entity: FSharpEntity * declarations: FSharpImplementationFileDeclaration list | MemberOrFunctionOrValue of value: FSharpMemberOrFunctionOrValue * curriedArgs: FSharpMemberOrFunctionOrValue list list * body: FSharpExpr | InitAction of action: FSharpExpr
<summary> Represents a declaration in an implementation file, as seen by the F# language </summary>

union case FSharpImplementationFileDeclaration.Entity: entity: FSharpEntity * declarations: FSharpImplementationFileDeclaration list -> FSharpImplementationFileDeclaration
<summary> Represents the declaration of a type </summary>

val e: FSharpEntity

val subDecls: FSharpImplementationFileDeclaration list

val printfn: format: Printf.TextWriterFormat<'T> -> 'T

property FSharpEntity.CompiledName: string with get
<summary> Get the compiled name of the type or module, possibly with `n mangling. This is identical to LogicalName unless the CompiledName attribute is used. </summary>

property List.Length: int with get

val subDecl: FSharpImplementationFileDeclaration

union case FSharpImplementationFileDeclaration.MemberOrFunctionOrValue: value: FSharpMemberOrFunctionOrValue * curriedArgs: FSharpMemberOrFunctionOrValue list list * body: FSharpExpr -> FSharpImplementationFileDeclaration
<summary> Represents the declaration of a member, function or value, including the parameters and body of the member </summary>

val v: FSharpMemberOrFunctionOrValue

val vs: FSharpMemberOrFunctionOrValue list list

val e: FSharpExpr

property FSharpMemberOrFunctionOrValue.CompiledName: string with get
<summary> Get the member name in compiled code </summary>

union case FSharpImplementationFileDeclaration.InitAction: action: FSharpExpr -> FSharpImplementationFileDeclaration
<summary> Represents the declaration of a static initialization action </summary>

property FSharpImplementationFileContents.Declarations: FSharpImplementationFileDeclaration list with get
<summary> Get the declarations that make up this implementation file </summary>

val myLibraryEntity: FSharpEntity

val myLibraryDecls: FSharpImplementationFileDeclaration list

val failwith: message: string -> 'T

val fooSymbol: FSharpMemberOrFunctionOrValue

val fooArgs: FSharpMemberOrFunctionOrValue list list

val fooExpression: FSharpExpr

property FSharpExpr.Type: FSharpType with get
<summary> The type of the expression </summary>

property FSharpExpr.Range: range with get
<summary> The range of the expression </summary>

val visitExpr: f: (FSharpExpr -> unit) -> e: FSharpExpr -> unit

val f: (FSharpExpr -> unit)

type FSharpExpr = member ImmediateSubExpressions: FSharpExpr list with get member Range: range with get member Type: FSharpType with get
<summary> Represents a checked and reduced expression, as seen by the F# language. The active patterns in 'FSharp.Compiler.SourceCodeServices' can be used to analyze information about the expression. Pattern matching is reduced to decision trees and conditional tests. Some other constructs may be represented in reduced form. </summary>

module FSharpExprPatterns from FSharp.Compiler.Symbols
<summary> A collection of active patterns to analyze expressions </summary>

active recognizer AddressOf: FSharpExpr -> FSharpExpr option
<summary> Matches expressions which take the address of a location </summary>

val lvalueExpr: FSharpExpr

active recognizer AddressSet: FSharpExpr -> (FSharpExpr * FSharpExpr) option
<summary> Matches expressions which set the contents of an address </summary>

val rvalueExpr: FSharpExpr

active recognizer Application: FSharpExpr -> (FSharpExpr * FSharpType list * FSharpExpr list) option
<summary> Matches expressions which are the application of function values </summary>

val funcExpr: FSharpExpr

val typeArgs: FSharpType list

val argExprs: FSharpExpr list

val visitExprs: f: (FSharpExpr -> unit) -> exprs: FSharpExpr list -> unit

active recognizer Call: FSharpExpr -> (FSharpExpr option * FSharpMemberOrFunctionOrValue * FSharpType list * FSharpType list * FSharpExpr list) option
<summary> Matches expressions which are calls to members or module-defined functions. When calling curried functions and members the arguments are collapsed to a single collection of arguments, as done in the compiled version of these. </summary>

val objExprOpt: FSharpExpr option

val memberOrFunc: FSharpMemberOrFunctionOrValue

val typeArgs1: FSharpType list

val typeArgs2: FSharpType list

val visitObjArg: f: (FSharpExpr -> unit) -> objOpt: FSharpExpr option -> unit

active recognizer Coerce: FSharpExpr -> (FSharpType * FSharpExpr) option
<summary> Matches expressions which coerce the type of a value </summary>

val targetType: FSharpType

val inpExpr: FSharpExpr

active recognizer FastIntegerForLoop: FSharpExpr -> (FSharpExpr * FSharpExpr * FSharpExpr * bool * FSharp.Compiler.Syntax.DebugPointAtFor * FSharp.Compiler.Syntax.DebugPointAtInOrTo) option
<summary> Matches fast-integer loops (up or down) </summary>

val startExpr: FSharpExpr

val limitExpr: FSharpExpr

val consumeExpr: FSharpExpr

val isUp: bool

active recognizer ILAsm: FSharpExpr -> (string * FSharpType list * FSharpExpr list) option
<summary> Matches expressions which are IL assembly code </summary>

val asmCode: string

active recognizer ILFieldGet: FSharpExpr -> (FSharpExpr option * FSharpType * string) option
<summary> Matches expressions which fetch a field from a .NET type </summary>

val fieldType: FSharpType

val fieldName: string

active recognizer ILFieldSet: FSharpExpr -> (FSharpExpr option * FSharpType * string * FSharpExpr) option
<summary> Matches expressions which set a field in a .NET type </summary>

val valueExpr: FSharpExpr

active recognizer IfThenElse: FSharpExpr -> (FSharpExpr * FSharpExpr * FSharpExpr) option
<summary> Matches expressions which are conditionals </summary>

val guardExpr: FSharpExpr

val thenExpr: FSharpExpr

val elseExpr: FSharpExpr

active recognizer Lambda: FSharpExpr -> (FSharpMemberOrFunctionOrValue * FSharpExpr) option
<summary> Matches expressions which are lambda abstractions </summary>

val lambdaVar: FSharpMemberOrFunctionOrValue

val bodyExpr: FSharpExpr

active recognizer Let: FSharpExpr -> ((FSharpMemberOrFunctionOrValue * FSharpExpr * FSharp.Compiler.Syntax.DebugPointAtBinding) * FSharpExpr) option
<summary> Matches expressions which are let definitions </summary>

val bindingVar: FSharpMemberOrFunctionOrValue

val bindingExpr: FSharpExpr

val dbg: FSharp.Compiler.Syntax.DebugPointAtBinding

active recognizer LetRec: FSharpExpr -> ((FSharpMemberOrFunctionOrValue * FSharpExpr * FSharp.Compiler.Syntax.DebugPointAtBinding) list * FSharpExpr) option
<summary> Matches expressions which are let-rec definitions </summary>

val recursiveBindings: (FSharpMemberOrFunctionOrValue * FSharpExpr * FSharp.Compiler.Syntax.DebugPointAtBinding) list

active recognizer NewArray: FSharpExpr -> (FSharpType * FSharpExpr list) option
<summary> Matches array expressions </summary>

val arrayType: FSharpType

active recognizer NewDelegate: FSharpExpr -> (FSharpType * FSharpExpr) option
<summary> Matches expressions which create an instance of a delegate type </summary>

val delegateType: FSharpType

val delegateBodyExpr: FSharpExpr

active recognizer NewObject: FSharpExpr -> (FSharpMemberOrFunctionOrValue * FSharpType list * FSharpExpr list) option
<summary> Matches expressions which are calls to object constructors </summary>

val objType: FSharpMemberOrFunctionOrValue

active recognizer NewRecord: FSharpExpr -> (FSharpType * FSharpExpr list) option
<summary> Matches record expressions </summary>

val recordType: FSharpType

active recognizer NewAnonRecord: FSharpExpr -> (FSharpType * FSharpExpr list) option
<summary> Matches anonymous record expressions </summary>

active recognizer NewTuple: FSharpExpr -> (FSharpType * FSharpExpr list) option
<summary> Matches tuple expressions </summary>

val tupleType: FSharpType

active recognizer NewUnionCase: FSharpExpr -> (FSharpType * FSharpUnionCase * FSharpExpr list) option
<summary> Matches expressions which create an object corresponding to a union case </summary>

val unionType: FSharpType

val unionCase: FSharpUnionCase

active recognizer Quote: FSharpExpr -> FSharpExpr option
<summary> Matches expressions which are quotation literals </summary>

val quotedExpr: FSharpExpr

active recognizer FSharpFieldGet: FSharpExpr -> (FSharpExpr option * FSharpType * FSharpField) option
<summary> Matches expressions which get a field from a record or class </summary>

val recordOrClassType: FSharpType

val fieldInfo: FSharpField

active recognizer AnonRecordGet: FSharpExpr -> (FSharpExpr * FSharpType * int) option
<summary> Matches expressions getting a field from an anonymous record. The integer represents the index into the sorted fields of the anonymous record. </summary>

val objExpr: FSharpExpr

val fieldInfo: int

active recognizer FSharpFieldSet: FSharpExpr -> (FSharpExpr option * FSharpType * FSharpField * FSharpExpr) option
<summary> Matches expressions which set a field in a record or class </summary>

val argExpr: FSharpExpr

active recognizer Sequential: FSharpExpr -> (FSharpExpr * FSharpExpr) option
<summary> Matches sequential expressions </summary>

val firstExpr: FSharpExpr

val secondExpr: FSharpExpr

active recognizer TryFinally: FSharpExpr -> (FSharpExpr * FSharpExpr * FSharp.Compiler.Syntax.DebugPointAtTry * FSharp.Compiler.Syntax.DebugPointAtFinally) option
<summary> Matches try/finally expressions </summary>

val finalizeExpr: FSharpExpr

val dbgTry: FSharp.Compiler.Syntax.DebugPointAtTry

val dbgFinally: FSharp.Compiler.Syntax.DebugPointAtFinally

active recognizer TryWith: FSharpExpr -> (FSharpExpr * FSharpMemberOrFunctionOrValue * FSharpExpr * FSharpMemberOrFunctionOrValue * FSharpExpr * FSharp.Compiler.Syntax.DebugPointAtTry * FSharp.Compiler.Syntax.DebugPointAtWith) option
<summary> Matches try/with expressions </summary>

val catchVar: FSharpMemberOrFunctionOrValue

val catchExpr: FSharpExpr

val dbgWith: FSharp.Compiler.Syntax.DebugPointAtWith

active recognizer TupleGet: FSharpExpr -> (FSharpType * int * FSharpExpr) option
<summary> Matches expressions which get a value from a tuple </summary>

val tupleElemIndex: int

val tupleExpr: FSharpExpr

active recognizer DecisionTree: FSharpExpr -> (FSharpExpr * (FSharpMemberOrFunctionOrValue list * FSharpExpr) list) option
<summary> Matches expressions with a decision expression, each branch of which ends in DecisionTreeSuccess passing control and values to one of the targets. </summary>

val decisionExpr: FSharpExpr

val decisionTargets: (FSharpMemberOrFunctionOrValue list * FSharpExpr) list

Multiple items
module List from Microsoft.FSharp.Collections

--------------------
type List<'T> = | op_Nil | op_ColonColon of Head: 'T * Tail: 'T list interface IReadOnlyList<'T> interface IReadOnlyCollection<'T> interface IEnumerable interface IEnumerable<'T> member GetReverseIndex: rank: int * offset: int -> int member GetSlice: startIndex: int option * endIndex: int option -> 'T list static member Cons: head: 'T * tail: 'T list -> 'T list member Head: 'T with get member IsEmpty: bool with get member Item: index: int -> 'T with get ...

val iter: action: ('T -> unit) -> list: 'T list -> unit

val snd: tuple: ('T1 * 'T2) -> 'T2

active recognizer DecisionTreeSuccess: FSharpExpr -> (int * FSharpExpr list) option
<summary> Special expressions at the end of a conditional decision structure in the decision expression node of a DecisionTree . The given expressions are passed as values to the decision tree target. </summary>

val decisionTargetIdx: int

val decisionTargetExprs: FSharpExpr list

active recognizer TypeLambda: FSharpExpr -> (FSharpGenericParameter list * FSharpExpr) option
<summary> Matches expressions which are type abstractions </summary>

val genericParam: FSharpGenericParameter list

active recognizer TypeTest: FSharpExpr -> (FSharpType * FSharpExpr) option
<summary> Matches expressions which test the runtime type of a value </summary>

val ty: FSharpType

active recognizer UnionCaseSet: FSharpExpr -> (FSharpExpr * FSharpType * FSharpUnionCase * FSharpField * FSharpExpr) option
<summary> Matches expressions which set a field from a union case (only used in FSharp.Core itself) </summary>

val unionExpr: FSharpExpr

val unionCaseField: FSharpField

active recognizer UnionCaseGet: FSharpExpr -> (FSharpExpr * FSharpType * FSharpUnionCase * FSharpField) option
<summary> Matches expressions which get a field from a union case </summary>

active recognizer UnionCaseTest: FSharpExpr -> (FSharpExpr * FSharpType * FSharpUnionCase) option
<summary> Matches expressions which test if an expression corresponds to a particular union case </summary>

active recognizer UnionCaseTag: FSharpExpr -> (FSharpExpr * FSharpType) option
<summary> Matches expressions which gets the tag for a union case </summary>

active recognizer ObjectExpr: FSharpExpr -> (FSharpType * FSharpExpr * FSharpObjectExprOverride list * (FSharpType * FSharpObjectExprOverride list) list) option
<summary> Matches object expressions, returning the base type, the base call, the overrides and the interface implementations </summary>

val objType: FSharpType

val baseCallExpr: FSharpExpr

val overrides: FSharpObjectExprOverride list

val interfaceImplementations: (FSharpType * FSharpObjectExprOverride list) list

val visitObjMember: f: (FSharpExpr -> unit) -> memb: FSharpObjectExprOverride -> unit

active recognizer TraitCall: FSharpExpr -> (FSharpType list * string * FSharp.Compiler.Syntax.SynMemberFlags * FSharpType list * FSharpType list * FSharpExpr list) option
<summary> Matches expressions for an unresolved call to a trait </summary>

val sourceTypes: FSharpType list

val traitName: string

val typeArgs: FSharp.Compiler.Syntax.SynMemberFlags

val typeInstantiation: FSharpType list

val argTypes: FSharpType list

active recognizer ValueSet: FSharpExpr -> (FSharpMemberOrFunctionOrValue * FSharpExpr) option
<summary> Matches expressions which set the contents of a mutable variable </summary>

val valToSet: FSharpMemberOrFunctionOrValue

active recognizer WhileLoop: FSharpExpr -> (FSharpExpr * FSharpExpr * FSharp.Compiler.Syntax.DebugPointAtWhile) option
<summary> Matches while loops </summary>

val dbg: FSharp.Compiler.Syntax.DebugPointAtWhile

active recognizer BaseValue: FSharpExpr -> FSharpType option
<summary> Matches expressions which are uses of the 'base' value </summary>

val baseType: FSharpType

active recognizer DefaultValue: FSharpExpr -> FSharpType option
<summary> Matches default-value expressions, including null expressions </summary>

val defaultType: FSharpType

active recognizer ThisValue: FSharpExpr -> FSharpType option
<summary> Matches expressions which are uses of the 'this' value </summary>

val thisType: FSharpType

active recognizer Const: FSharpExpr -> (obj * FSharpType) option
<summary> Matches constant expressions, including signed and unsigned integers, strings, characters, booleans, arrays of bytes and arrays of unit16. </summary>

val constValueObj: obj

val constType: FSharpType

active recognizer Value: FSharpExpr -> FSharpMemberOrFunctionOrValue option
<summary> Matches expressions which are uses of values </summary>

val valueToGet: FSharpMemberOrFunctionOrValue

val sprintf: format: Printf.StringFormat<'T> -> 'T

val exprs: FSharpExpr list

val objOpt: FSharpExpr option

module Option from Microsoft.FSharp.Core

val iter: action: ('T -> unit) -> option: 'T option -> unit

val memb: FSharpObjectExprOverride

property FSharpObjectExprOverride.Body: FSharpExpr with get
<summary> The expression that forms the body of the method </summary>