F# Compiler service's visitor pattern library

• TODO: This project is still work in progress, and need more documents.

Status

NuGet
CI (AppVeyor)
Issue status
Pull req

What is this?

• We can apply visitor pattern with minimum coding for FSharp.Compiler.Service's untyped ASTs.
• Contains two visitors:
  • "Functional visitor types. (FP based)"
  • "Inheritable (Legacy) visitor base class. (OOP based)"
• FSharp.Compiler.Service.Visitors is part of fscx-project.

Functional visitor implementation:

• "Functional visitor" is using for functional visitor patterns with F#'s AST (FSharp.Compiler.Services untyped AST).

// Functional visitor pattern (Not use custom context):
let outerVisitor
   (defaultVisitor: (NoContext * SynExpr -> SynExpr),
    context: NoContext,  // (Non custom context type)
    expr: SynExpr) : SynExpr option =

  match expr with
  | SynExpr.Quote(operator, _, _, _, _) ->
    // DEBUG
    printfn "%A" operator
    None  // (None is default visiting)

  | SynExpr.App(exprAtomicFlag, isInfix, funcExpr, argExpr, range) ->
    match funcExpr with
      // ...

  | _ ->
    None  // (None is default visiting)
 
// Declare your own functional visitor.
// Type name for free.
type InsertLoggingVisitor() =
  inherit DeclareAstFunctionalVisitor(outerVisitor)

Inheritable visitor implementation:

• "Inheritable visitor" is using for traditional visitor patterns with F#'s AST.
  • If you are implemented visitor class inherit from "AstInheritableVisitor" class.
  • "AstInheritableVisitor" are abstract classes, generic version and non-generic version.
  • Generic argument is "Context type". Context is depending any information holds for your implementations. Implicit applied "NoContext" type for non-generic version.
  • This class likely "System.Linq.Expressions.ExpressionVisitor" class.

// Inheritable visitor pattern (Not use custom context):
// Type name for free.
type InsertLoggingVisitor() =
  inherit AstInheritableVisitor()

  override __.VisitExpr_Quote(context, operator, isRaw, quoteSynExpr, isFromQueryExpression, range) =
    // DEBUG
    printfn "%A" operator
    base.VisitExpr_Quote(context, operator, isRaw, quoteSynExpr, isFromQueryExpression, range)

  override this.VisitExpr_App(context, exprAtomicFlag, isInfix, funcExpr, argExpr, range) =
    match funcExpr with
      // ...

• Default visiting is derivng from AstInheritableVisitor class.
• Hooking point are "BeforeVisit*" or "Visit*".
  • "BeforeVisit" is givening for all NON-VISITED args.
  • "Visit" is givening for all VISITED args.

Library depends

• FSharp.Core >= 4.1.17
• FSharp.Compiler.Service >= 12.0.8

Maintainers

• Kouji Matsui twitter
• bleis-tift twitter

History

• 0.9.1:
  • FCS upgraded to 12.0.8.
• 0.7.3:
  • Fixed System.Collections.Immutable version.
• 0.7.2:
  • Pinned version 1.4.2 for System.Reflection.Metadata (non-beta)
• 0.7.1:
  • Manage parent nodes using list instead stack.
  • Remove FSharpCheckFileResults args.
  • Update readme.
• 0.6.3:
  • Reduced context type constraints.
• 0.6.2:
  • Moved non generic AstInheritableVisitor.
• 0.6.1:
  • Upgraded to FSharp.Compiler Service 6.0.2 (You must be rearrenging for NuGet package installation with -Pre option, because 6.0.2 depends for System.Reflection.Metadata.dll BETA package.)
• 0.5.1:
  • Moving implements from FSharp.Expandable.Compiler.Core.
  • Code neutralize.