feat: add Fable.Types module for runtime type detection

Add utilities for detecting Fable types at runtime in Python:
- typeName: get Python type name of an object
- isIntegralType: check for Int8-64, UInt8-64
- isNumericType: check for integral types + Float32/64
- isArrayType: check for FSharpArray, GenericArray, typed arrays

Also includes code formatting improvements and test coverage.

Release-As: 5.0.0-alpha.21.3

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: dbrattli

.markdownlint.json

@@ -0,0 +1,3 @@
+{
+  "MD024": false
+}

CHANGELOG.md

@@ -2,12 +2,10 @@
 
 ## [5.0.0-alpha.21.1](https://github.com/fable-compiler/Fable.Python/compare/v5.0.0-alpha.21.0...v5.0.0-alpha.21.1) (2025-12-18)
 
-
 ### Features
 
 * Add Json static class with Fable-aware serialization ([#175](https://github.com/fable-compiler/Fable.Python/issues/175)) ([1eb5005](https://github.com/fable-compiler/Fable.Python/commit/1eb500523c6d6f43247bc3510a6045ec8d9d9d4e))
 
-
 ### Bug Fixes
 
 * correct manifest to last released version ([bb9cb88](https://github.com/fable-compiler/Fable.Python/commit/bb9cb881c00b7ea6809ad3a87a35a7ebc0ff9008))
@@ -16,7 +14,6 @@
 
 ## [5.0.0-alpha.21.0](https://github.com/fable-compiler/Fable.Python/compare/v5.0.0-alpha.21...v5.0.0-alpha.21.0) (2025-12-16)
 
-
 ### Features
 
 * Add exception types ([#173](https://github.com/fable-compiler/Fable.Python/issues/173)) ([72f09b2](https://github.com/fable-compiler/Fable.Python/commit/72f09b2ff6e208e3ab057430a355814611abd46c))
@@ -26,7 +23,6 @@
 * Fable v5 ([#147](https://github.com/fable-compiler/Fable.Python/issues/147)) ([abf8e6a](https://github.com/fable-compiler/Fable.Python/commit/abf8e6a1f7bbc2eae152431d04d6b8b5675f7795))
 * FastAPI async handlers ([#174](https://github.com/fable-compiler/Fable.Python/issues/174)) ([26cec1f](https://github.com/fable-compiler/Fable.Python/commit/26cec1f239f9244a7c1da1d00bbf1a479596bb3c))
 
-
 ### Bug Fixes
 
 * add missing models.py for pydantic example and update README ([#168](https://github.com/fable-compiler/Fable.Python/issues/168)) ([b76ce98](https://github.com/fable-compiler/Fable.Python/commit/b76ce989e0598d0007a8a1be9addfea97936eae7))
@@ -36,35 +32,30 @@
 * use plain int/string types for open ([b202a25](https://github.com/fable-compiler/Fable.Python/commit/b202a25bd7f48538fadc50125294a9252714d364))
 * use string types for open ([f211f8b](https://github.com/fable-compiler/Fable.Python/commit/f211f8bb9445dd6930926fe48aab6a69720dd30f))
 
-
 ### Miscellaneous Chores
 
 * sync with Fable 5.0.0-alpha.21 ([fd2685c](https://github.com/fable-compiler/Fable.Python/commit/fd2685c2f992c2d8058ac1bc1261d647271359df))
 
 ## [5.0.0-alpha.20.2](https://github.com/fable-compiler/Fable.Python/compare/v5.0.0-alpha.20.1...v5.0.0-alpha.20.2) (2025-12-09)
 
-
 ### Features
 
 * add Python stdlib bindings for logging, random, and expand string module ([#166](https://github.com/fable-compiler/Fable.Python/issues/166)) ([709d6c2](https://github.com/fable-compiler/Fable.Python/commit/709d6c2b29199965926ff639727fdcc1bb2e1fb8))
 
 ## [5.0.0-alpha.20.1](https://github.com/fable-compiler/Fable.Python/compare/v5.0.0-alpha.20...v5.0.0-alpha.20.1) (2025-12-08)
 
-
 ### Bug Fixes
 
 * relax FSharp.Core dependency to >= 5.0.0 ([#163](https://github.com/fable-compiler/Fable.Python/issues/163)) ([10eb65b](https://github.com/fable-compiler/Fable.Python/commit/10eb65b22a157078e1b66bd8fb202b0cd2acbedc))
 
 ## [5.0.0-alpha.20](https://github.com/fable-compiler/Fable.Python/compare/v5.0.0-alpha.20...v5.0.0-alpha.20) (2025-12-08)
 
-
 ### Features
 
 * add write ([334e800](https://github.com/fable-compiler/Fable.Python/commit/334e80089c081bda25633f83dae037fc6c8fe6f5))
 * Added bindings for Pydantic and FastAPI + examples ([#151](https://github.com/fable-compiler/Fable.Python/issues/151)) ([826629e](https://github.com/fable-compiler/Fable.Python/commit/826629e465fca15d444a4ca37b851b8aab488f9a))
 * Fable v5 ([#147](https://github.com/fable-compiler/Fable.Python/issues/147)) ([abf8e6a](https://github.com/fable-compiler/Fable.Python/commit/abf8e6a1f7bbc2eae152431d04d6b8b5675f7795))
 
-
 ### Bug Fixes
 
 * handle return type correctly ([a634168](https://github.com/fable-compiler/Fable.Python/commit/a6341684ac8bb3f1b244f448c22e1fe6f208fbc0))

src/Fable.Python.fsproj

@@ -36,6 +36,8 @@
 
     <Compile Include="pydantic/Pydantic.fs" />
     <Compile Include="fastapi/FastAPI.fs" />
+
+    <Compile Include="fable/Types.fs" />
   </ItemGroup>
   <ItemGroup>
     <Content Include="pyproject.toml; *.fsproj; **\*.fs; **\*.fsi" PackagePath="fable\" />

src/fable/Types.fs

@@ -0,0 +1,55 @@
+/// Utilities for detecting and working with Fable types at runtime in Python.
+/// These helpers are useful when you need to distinguish between native Python types
+/// and Fable-compiled F# types (e.g., Int32, Float64, FSharpArray).
+module Fable.Python.Fable.Types
+
+open Fable.Core
+
+/// Get the Python type name of an object
+[<Emit("type($0).__name__")>]
+let typeName (o: obj) : string = nativeOnly
+
+/// Check if an object is a Fable integral type (Int8, Int16, Int32, Int64, UInt8, UInt16, UInt32, UInt64)
+let isIntegralType (o: obj) : bool =
+    match typeName o with
+    | "Int8"
+    | "Int16"
+    | "Int32"
+    | "Int64"
+    | "UInt8"
+    | "UInt16"
+    | "UInt32"
+    | "UInt64" -> true
+    | _ -> false
+
+/// Check if an object is a Fable numeric type (integral types + Float32, Float64)
+let isNumericType (o: obj) : bool =
+    match typeName o with
+    | "Int8"
+    | "Int16"
+    | "Int32"
+    | "Int64"
+    | "UInt8"
+    | "UInt16"
+    | "UInt32"
+    | "UInt64"
+    | "Float32"
+    | "Float64" -> true
+    | _ -> false
+
+/// Check if an object is a Fable array type (FSharpArray, GenericArray, or typed arrays)
+let isArrayType (o: obj) : bool =
+    match typeName o with
+    | "FSharpArray"
+    | "GenericArray"
+    | "Int8Array"
+    | "Int16Array"
+    | "Int32Array"
+    | "Int64Array"
+    | "UInt8Array"
+    | "UInt16Array"
+    | "UInt32Array"
+    | "UInt64Array"
+    | "Float32Array"
+    | "Float64Array" -> true
+    | _ -> false

src/fastapi/FastAPI.fs

@@ -136,33 +136,27 @@ type RouterWebSocketAttribute(path: string) =
 
 /// JSON response class
 [<Import("JSONResponse", "fastapi.responses")>]
-type JSONResponse(content: obj, ?status_code: int) =
-    class end
+type JSONResponse(content: obj, ?status_code: int) = class end
 
 /// HTML response class
 [<Import("HTMLResponse", "fastapi.responses")>]
-type HTMLResponse(content: string, ?status_code: int) =
-    class end
+type HTMLResponse(content: string, ?status_code: int) = class end
 
 /// Plain text response class
 [<Import("PlainTextResponse", "fastapi.responses")>]
-type PlainTextResponse(content: string, ?status_code: int) =
-    class end
+type PlainTextResponse(content: string, ?status_code: int) = class end
 
 /// Redirect response class
 [<Import("RedirectResponse", "fastapi.responses")>]
-type RedirectResponse(url: string, ?status_code: int) =
-    class end
+type RedirectResponse(url: string, ?status_code: int) = class end
 
 /// Streaming response class
 [<Import("StreamingResponse", "fastapi.responses")>]
-type StreamingResponse(content: obj, ?media_type: string) =
-    class end
+type StreamingResponse(content: obj, ?media_type: string) = class end
 
 /// File response class
 [<Import("FileResponse", "fastapi.responses")>]
-type FileResponse(path: string, ?filename: string, ?media_type: string) =
-    class end
+type FileResponse(path: string, ?filename: string, ?media_type: string) = class end
 
 // ============================================================================
 // Request and WebSocket
@@ -256,8 +250,7 @@ type WebSocket() =
 
 /// HTTP exception for returning error responses
 [<Import("HTTPException", "fastapi")>]
-type HTTPException(status_code: int, ?detail: string) =
-    class end
+type HTTPException(status_code: int, ?detail: string) = class end
 
 // ============================================================================
 // Dependency Injection
@@ -422,7 +415,7 @@ type UploadFile() =
 /// File parameter marker
 [<Import("File", "fastapi")>]
 [<Emit("$0()")>]
-let File() : UploadFile = nativeOnly
+let File () : UploadFile = nativeOnly
 
 /// Form parameter marker
 [<Import("Form", "fastapi")>]
@@ -452,7 +445,10 @@ type APIRouter(?prefix: string, ?tags: ResizeArray<string>) =
 
     /// Include another router with prefix and tags
     [<Emit("$0.include_router($1, prefix=$2, tags=$3)")>]
-    member _.include_router_with_prefix_and_tags(_router: APIRouter, _prefix: string, _tags: ResizeArray<string>) : unit = nativeOnly
+    member _.include_router_with_prefix_and_tags
+        (_router: APIRouter, _prefix: string, _tags: ResizeArray<string>)
+        : unit =
+        nativeOnly
 
 // ============================================================================
 // FastAPI Application
@@ -471,7 +467,10 @@ type FastAPI(?title: string, ?description: string, ?version: string) =
 
     /// Include a router with prefix and tags
     [<Emit("$0.include_router($1, prefix=$2, tags=$3)")>]
-    member _.include_router_with_prefix_and_tags(_router: APIRouter, _prefix: string, _tags: ResizeArray<string>) : unit = nativeOnly
+    member _.include_router_with_prefix_and_tags
+        (_router: APIRouter, _prefix: string, _tags: ResizeArray<string>)
+        : unit =
+        nativeOnly
 
     /// Add middleware
     [<Emit("$0.add_middleware($1)")>]
@@ -571,8 +570,7 @@ type OAuth2PasswordRequestForm() =
 
 /// HTTP Basic authentication
 [<Import("HTTPBasic", "fastapi.security")>]
-type HTTPBasic() =
-    class end
+type HTTPBasic() = class end
 
 /// HTTP Basic credentials
 [<Import("HTTPBasicCredentials", "fastapi.security")>]
@@ -587,8 +585,7 @@ type HTTPBasicCredentials() =
 
 /// HTTP Bearer authentication
 [<Import("HTTPBearer", "fastapi.security")>]
-type HTTPBearer() =
-    class end
+type HTTPBearer() = class end
 
 /// HTTP Bearer credentials (token in Authorization header)
 [<Import("HTTPAuthorizationCredentials", "fastapi.security")>]
@@ -603,27 +600,23 @@ type HTTPAuthorizationCredentials() =
 
 /// API Key in header
 [<Import("APIKeyHeader", "fastapi.security")>]
-type APIKeyHeader(name: string) =
-    class end
+type APIKeyHeader(name: string) = class end
 
 /// API Key in query parameter
 [<Import("APIKeyQuery", "fastapi.security")>]
-type APIKeyQuery(name: string) =
-    class end
+type APIKeyQuery(name: string) = class end
 
 /// API Key in cookie
 [<Import("APIKeyCookie", "fastapi.security")>]
-type APIKeyCookie(name: string) =
-    class end
+type APIKeyCookie(name: string) = class end
 
 // ============================================================================
 // CORS Middleware
 // ============================================================================
 
 /// CORS middleware for handling Cross-Origin Resource Sharing
 [<Import("CORSMiddleware", "fastapi.middleware.cors")>]
-type CORSMiddleware =
-    class end
+type CORSMiddleware = class end
 
 /// CORS middleware configuration helper
 module CORSMiddleware =
@@ -634,7 +627,15 @@ module CORSMiddleware =
 
     /// Add CORS middleware to app with all origins allowed
     [<Emit("$0.add_middleware($1, allow_origins=$2, allow_credentials=$3, allow_methods=$4, allow_headers=$5)")>]
-    let addToApp (_app: FastAPI) (_middleware: obj) (_origins: string array) (_credentials: bool) (_methods: string array) (_headers: string array) : unit = nativeOnly
+    let addToApp
+        (_app: FastAPI)
+        (_middleware: obj)
+        (_origins: string array)
+        (_credentials: bool)
+        (_methods: string array)
+        (_headers: string array)
+        : unit =
+        nativeOnly
 
 // ============================================================================
 // Encoders

src/flask/Flask.fs

@@ -259,8 +259,7 @@ let make_response_with_status (_body: obj) (_status: int) : Response = nativeOnl
 
 /// Flask Blueprint for modular applications
 [<Import("Blueprint", "flask")>]
-type Blueprint(name: string, import_name: string, ?url_prefix: string) =
-    class end
+type Blueprint(name: string, import_name: string, ?url_prefix: string) = class end
 
 // ============================================================================
 // Flask Application

src/pydantic/Pydantic.fs

@@ -458,4 +458,3 @@ type Base64Str = string
 /// JSON type - validates JSON string and parses it
 [<Import("Json", "pydantic")>]
 type JsonValue = obj
-

src/stdlib/Json.fs

@@ -15,24 +15,28 @@ type IExports =
     /// Serialize obj to a JSON formatted string with indentation
     /// See https://docs.python.org/3/library/json.html#json.dumps
     abstract dumps: obj: obj * indent: int -> string
+
     /// Serialize obj to a JSON formatted string with a custom default function
     /// See https://docs.python.org/3/library/json.html#json.dumps
     [<NamedParams(fromIndex = 1)>]
     abstract dumps: obj: obj * ``default``: (obj -> obj) -> string
+
     /// Serialize obj to a JSON formatted string with indentation and custom default
     /// See https://docs.python.org/3/library/json.html#json.dumps
     [<NamedParams(fromIndex = 1)>]
     abstract dumps: obj: obj * indent: int * ``default``: (obj -> obj) -> string
+
     /// Serialize obj to a JSON formatted string with separators, ensure_ascii, and custom default
     /// See https://docs.python.org/3/library/json.html#json.dumps
     [<NamedParams(fromIndex = 1)>]
-    abstract dumps:
-        obj: obj * separators: string array * ensure_ascii: bool * ``default``: (obj -> obj) -> string
+    abstract dumps: obj: obj * separators: string array * ensure_ascii: bool * ``default``: (obj -> obj) -> string
+
     /// Serialize obj to a JSON formatted string with indent, separators, ensure_ascii, and custom default
     /// See https://docs.python.org/3/library/json.html#json.dumps
     [<NamedParams(fromIndex = 1)>]
     abstract dumps:
         obj: obj * indent: int * separators: string array * ensure_ascii: bool * ``default``: (obj -> obj) -> string
+
     /// Deserialize a JSON document from a string to a Python object
     /// See https://docs.python.org/3/library/json.html#json.loads
     abstract loads: s: string -> obj
@@ -42,14 +46,17 @@ type IExports =
     /// Serialize obj as a JSON formatted stream with indentation
     /// See https://docs.python.org/3/library/json.html#json.dump
     abstract dump: obj: obj * fp: TextIOWrapper * indent: int -> unit
+
     /// Serialize obj as a JSON formatted stream with a custom default function
     /// See https://docs.python.org/3/library/json.html#json.dump
     [<NamedParams(fromIndex = 2)>]
     abstract dump: obj: obj * fp: TextIOWrapper * ``default``: (obj -> obj) -> unit
+
     /// Serialize obj as a JSON formatted stream with indentation and custom default
     /// See https://docs.python.org/3/library/json.html#json.dump
     [<NamedParams(fromIndex = 2)>]
     abstract dump: obj: obj * fp: TextIOWrapper * indent: int * ``default``: (obj -> obj) -> unit
+
     /// Deserialize a JSON document from a file-like object to a Python object
     /// See https://docs.python.org/3/library/json.html#json.load
     abstract load: fp: TextIOWrapper -> obj
@@ -127,7 +134,13 @@ let fableDefault (o: obj) : obj =
         if hasattr o "tag" && hasattr o "fields" then
             let cases = getCases o
             let tag: int = getattr o "tag" :?> int
-            let caseName = if tag < cases.Length then cases.[tag] else "Case" + string tag
+
+            let caseName =
+                if tag < cases.Length then
+                    cases.[tag]
+                else
+                    "Case" + string tag
+
             unionToList o caseName
         elif hasattr o "__slots__" then
             slotsToDict o
@@ -152,7 +165,13 @@ type Json =
 
     /// Serialize obj to JSON with indentation, custom separators, and ensure_ascii, automatically handling Fable types
     static member inline dumps(obj: obj, indent: int, separators: string array, ensureAscii: bool) : string =
-        json.dumps (obj, indent = indent, separators = separators, ensure_ascii = ensureAscii, ``default`` = fableDefault)
+        json.dumps (
+            obj,
+            indent = indent,
+            separators = separators,
+            ensure_ascii = ensureAscii,
+            ``default`` = fableDefault
+        )
 
     /// Serialize obj as JSON stream to file, automatically handling Fable types
     static member inline dump(obj: obj, fp: TextIOWrapper) : unit =
@@ -163,9 +182,7 @@ type Json =
         json.dump (obj, fp, indent, ``default`` = fableDefault)
 
     /// Deserialize a JSON document from a string to a Python object
-    static member inline loads(s: string) : obj =
-        json.loads s
+    static member inline loads(s: string) : obj = json.loads s
 
     /// Deserialize a JSON document from a file-like object to a Python object
-    static member inline load(fp: TextIOWrapper) : obj =
-        json.load fp
+    static member inline load(fp: TextIOWrapper) : obj = json.load fp