[JS/TS] Add F# quotation support with serializable QuotExpr AST#4474

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OnurGumus wants to merge 2 commits intofable-compiler:mainfrom

OnurGumus:quotation-support

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OnurGumus commented Apr 2, 2026

Summary

Add support for F# code quotations (<@ expr @> and <@@ expr @@>) targeting JS/TS
Quotations compile to a serializable QuotExpr discriminated union (defined in Fable.Core.Quotations)
Designed for cross-platform JSON serialization via Thoth.Json / Fable.Remoting between Fable clients and .NET backends
The % splice operator is supported for composing quotations
Other targets (Python, Rust, Dart, Beam, PHP) have stubs with error messages

Supported quotation nodes

Values (int, float, string, char, bool, unit, null), lambdas, let/letrec bindings, if/then/else, function calls, operators, tuples, unions, records, options, lists, sequential, variable set, field get/set

New files

File	Purpose
`src/Fable.Core/Fable.Core.Quotations.fs`	Shared F# DU types (`QuotExpr`, `QuotVar`, `QuotLiteral`) for .NET deserialization
`src/fable-library-ts/Quotation.ts`	JS/TS runtime with Union subclasses, reflection info, and `quotExprFromJSON` deserializer
`src/Fable.Transforms/QuotationEmitter.fs`	Compiler transform: Fable `Quote` AST → runtime constructor calls
`tests/Js/Main/QuotationTests.fs`	18 tests including structural verification, splice composition, and JSON round-trip

Usage

// Fable client — construct and serialize
let q = <@ fun x -> x + 1 @>
let json = JS.JSON.stringify(q)
// → ["Lambda",{"Name":"x","Type":"System.Int32","IsMutable":false},["Call",null,"op_Addition",...]]

// .NET backend — deserialize (add Fable.Core NuGet)
open Fable.Core.Quotations
let expr = Thoth.Json.Net.Decode.Auto.fromString<QuotExpr>(json)

Test plan

All 2805 JS tests pass (0 failing)
All 2642 .NET tests pass (0 errored)
TypeScript quicktest compiles and runs
Structural tests verify quotation AST shape (case names, field values)
Splice (%) tests verify expression composition
JSON serialization round-trip test
Manual test with Thoth.Json on .NET side

🤖 Generated with Claude Code


          [JS/TS] Add F# quotation support with serializable QuotExpr AST

a63ded8

Add support for F# code quotations (<@ expr @> and <@@ expr @@>) targeting
JS/TS. Quotations compile to a serializable QuotExpr discriminated union
that works with Thoth.Json and Fable.Remoting for cross-platform
serialization between Fable clients and .NET backends.

Supported quotation nodes: values (int, float, string, char, bool, unit),
lambdas, let bindings, if/then/else, function calls, operators, tuples,
unions, records, options, lists, sequential, variable set, field get/set.

The % splice operator is supported for composing quotations.

New files:
- Fable.Core.Quotations.fs: shared F# DU types for .NET deserialization
- Quotation.ts: JS/TS runtime with proper Union subclasses
- QuotationEmitter.fs: compiler transform from Fable Quote AST to runtime calls
- QuotationTests.fs: test suite

Other targets (Python, Rust, Dart, Beam, PHP) have stubs with error messages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Collaborator

dbrattli commented Apr 2, 2026

Nice! We should coordinate / align this with #4474

This was referenced Apr 3, 2026

[Python] Fix unsafe option unwrapping in Replacements.fs #4480

Merged

CLIEvent and Object expressions #3039

Open

[Repo Assist] Monthly Activity 2026-04 #4471

Open

github-advanced-security bot found potential problems

View reviewed changes

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                  | Unit -> "Microsoft.FSharp.Core.Unit"
+                  | Any -> "System.Object"
+                  | LambdaType(argType, returnType) ->
+                      $"Microsoft.FSharp.Core.FSharpFunc`2[{typeToString argType},{typeToString returnType}]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                  | Unit -> "Microsoft.FSharp.Core.Unit"
+                  | Any -> "System.Object"
+                  | LambdaType(argType, returnType) ->
+                      $"Microsoft.FSharp.Core.FSharpFunc`2[{typeToString argType},{typeToString returnType}]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                      $"Microsoft.FSharp.Core.FSharpFunc`2[{typeToString argType},{typeToString returnType}]"
+                  | Tuple(genArgs, _) ->
+                      let args = genArgs |> List.map typeToString |> String.concat ","
+                      $"System.Tuple`{genArgs.Length}[{args}]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                      $"Microsoft.FSharp.Core.FSharpFunc`2[{typeToString argType},{typeToString returnType}]"
+                  | Tuple(genArgs, _) ->
+                      let args = genArgs |> List.map typeToString |> String.concat ","
+                      $"System.Tuple`{genArgs.Length}[{args}]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                      let args = genArgs |> List.map typeToString |> String.concat ","
+                      $"System.Tuple`{genArgs.Length}[{args}]"
+                  | DeclaredType(entRef, _genArgs) -> entRef.FullName
+                  | Option(genArg, _) -> $"Microsoft.FSharp.Core.FSharpOption`1[{typeToString genArg}]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                      $"System.Tuple`{genArgs.Length}[{args}]"
+                  | DeclaredType(entRef, _genArgs) -> entRef.FullName
+                  | Option(genArg, _) -> $"Microsoft.FSharp.Core.FSharpOption`1[{typeToString genArg}]"
+                  | List genArg -> $"Microsoft.FSharp.Collections.FSharpList`1[{typeToString genArg}]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                  | DeclaredType(entRef, _genArgs) -> entRef.FullName
+                  | Option(genArg, _) -> $"Microsoft.FSharp.Core.FSharpOption`1[{typeToString genArg}]"
+                  | List genArg -> $"Microsoft.FSharp.Collections.FSharpList`1[{typeToString genArg}]"
+                  | Array(genArg, _) -> $"{typeToString genArg}[]"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

src/Fable.Transforms/QuotationEmitter.fs Outdated

+                  Helper.LibCall(com, "Quotation", "mkValue", Any, [ lit ])
+              and private emitUnsupported (com: Compiler) (nodeName: string) : Expr =
+                  let msg = $"Unsupported quotation node: {nodeName}"

Check warning

Code scanning / Ionide.Analyzers.Cli

Warns about missing type specifiers in interpolated strings Warning

Interpolated hole expression without format detected. Use prefix with the correct % to enforce type safety.

ncave reviewed

View reviewed changes

src/Fable.Transforms/Fable.Transforms.fsproj Show resolved Hide resolved

dbrattli added a commit that referenced this pull request


          Align quotation function names with JS PR #4474

371052e

Rename to match #4474 conventions so it can rebase cleanly:
- mkVarExpr -> mkVar (Expr.Var), mkVar -> mkQuotVar (Var constructor)
- mkApp -> mkApplication
- isNewUnion -> isNewUnionCase

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dbrattli added a commit that referenced this pull request


          Rename quotation module to "quotation" across all targets

Use "quotation" as the canonical module name:
- Python: quotation.py (renamed from fable_quotation.py)
- Beam: fable_quotation.erl (fable_ prefix added by getLibPath)
- JS (#4474): Quotation.ts (natural mapping)

Revert the Beam getLibPath workaround as it's no longer needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Collaborator

dbrattli commented Apr 4, 2026 •

edited

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I have fixed #4398 so that the common code will work for JS/TS as well. Thus can be reused by this PR, so most changes to Replacements.fs will not be needed. @MangelMaxime @ncave. If we are good with adding Quotations then I can merge my PR? Then this PR will be much simpler on top of that.


          Fix standalone build and interpolated string analyzer warnings

7264c80

Add QuotationEmitter.fs to Fable.Standalone.fsproj and add type-safe
format specifiers to interpolated strings in QuotationEmitter.fs.

Contributor Author

OnurGumus commented Apr 4, 2026

@dbrattli by all means that's fine by me. probably better as my pr only targets js/ts as of now.

Collaborator

dbrattli commented Apr 4, 2026

@OnurGumus Ok, let us just check with @MangelMaxime that we are ok with the Fable.AST change at this point since it may break extensions.

dbrattli mentioned this pull request

[Python/Beam] Add F# quotation support (<@ ... @>) #4398

Open

4 tasks

This was referenced Apr 6, 2026

[JavaScript / Python] Make a pass to implement missing pre-defined Date format #3976

Open

[Repo Assist] chore: add Dependabot configuration for automated dependency updates #4489

Open

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