diff --git a/src/stdlib/Builtins.fs b/src/stdlib/Builtins.fs
index dbe193a..194b275 100644
--- a/src/stdlib/Builtins.fs
+++ b/src/stdlib/Builtins.fs
@@ -186,11 +186,12 @@ type IExports =
 
     /// Make an iterator that computes the function using arguments from each
     /// of the iterables.  Stops when the shortest iterable is exhausted.
-    abstract map: ('T1 * 'T2 -> 'T3) * IEnumerable<'T1> * IEnumerable<'T2> -> IEnumerable<'T3>
+    abstract map: System.Func<'T1, 'T2, 'T3> * IEnumerable<'T1> * IEnumerable<'T2> -> IEnumerable<'T3>
 
     /// Make an iterator that computes the function using arguments from each
     /// of the iterables.  Stops when the shortest iterable is exhausted.
-    abstract map: ('T1 * 'T2 * 'T3 -> 'T4) * IEnumerable<'T1> * IEnumerable<'T2> * IEnumerable<'T3> -> IEnumerable<'T4>
+    abstract map:
+        System.Func<'T1, 'T2, 'T3, 'T4> * IEnumerable<'T1> * IEnumerable<'T2> * IEnumerable<'T3> -> IEnumerable<'T4>
 
     /// Return the Unicode code point for a one-character string.
     abstract ord: char -> int
diff --git a/test/TestBuiltins.fs b/test/TestBuiltins.fs
index 5af0fc8..d2c4a69 100644
--- a/test/TestBuiltins.fs
+++ b/test/TestBuiltins.fs
@@ -120,3 +120,107 @@ let ``test pyNone is None`` () =
     builtins.bool pyNone |> equal false
     // None has type NoneType, so isinstance(None, type(None)) holds
     builtins.isinstance (pyNone, builtins.``type`` pyNone) |> equal true
+
+[<Fact>]
+let ``test abs with int works`` () =
+    builtins.abs -5 |> equal 5
+    builtins.abs 0 |> equal 0
+    builtins.abs 42 |> equal 42
+
+[<Fact>]
+let ``test abs with float works`` () =
+    builtins.abs -3.14 |> equal 3.14
+    builtins.abs 0.0 |> equal 0.0
+    builtins.abs 2.72 |> equal 2.72
+
+[<Fact>]
+let ``test chr and ord round-trip works`` () =
+    builtins.chr 65 |> equal 'A'
+    builtins.chr 97 |> equal 'a'
+    builtins.ord 'A' |> equal 65
+    builtins.ord 'a' |> equal 97
+
+[<Fact>]
+let ``test chr ord round-trip preserves value`` () =
+    let code = 9731 // snowman ☃
+    builtins.ord (builtins.chr code) |> equal code
+
+[<Fact>]
+let ``test len with list works`` () =
+    // F# `int list` compiles to FSharpList (no __len__); convert via builtins.list.
+    builtins.len (builtins.list (seq { 1..3 })) |> equal 3
+    builtins.len (builtins.list Seq.empty<int>) |> equal 0
+
+[<Fact>]
+let ``test len with string works`` () =
+    builtins.len ("hello" |> box) |> equal 5
+    builtins.len ("" |> box) |> equal 0
+
+[<Fact>]
+let ``test map with single iterable works`` () =
+    builtins.map ((fun x -> x * 2), [ 1; 2; 3 ])
+    |> Seq.toList
+    |> equal [ 2; 4; 6 ]
+
+[<Fact>]
+let ``test map with two iterables works`` () =
+    builtins.map ((fun a b -> a + b), [ 1; 2; 3 ], [ 10; 20; 30 ])
+    |> Seq.toList
+    |> equal [ 11; 22; 33 ]
+
+[<Fact>]
+let ``test map with three iterables works`` () =
+    builtins.map ((fun a b c -> a + b + c), [ 1; 2; 3 ], [ 10; 20; 30 ], [ 100; 200; 300 ])
+    |> Seq.toList
+    |> equal [ 111; 222; 333 ]
+
+[<Fact>]
+let ``test str conversion works`` () =
+    builtins.str 42 |> equal "42"
+    builtins.str true |> equal "True"
+
+[<Fact>]
+let ``test int conversion works`` () =
+    builtins.int "42" |> equal 42
+    builtins.int 3.9 |> equal 3
+    // Python's int() truncates toward zero, not floor
+    builtins.int -3.9 |> equal -3
+
+[<Fact>]
+let ``test float conversion works`` () =
+    builtins.float "3.14" |> equal 3.14
+    builtins.float 42 |> equal 42.0
+
+[<Fact>]
+let ``test isinstance works`` () =
+    let pyIntVal: obj = emitPyExpr () "42"
+    let pyStrVal: obj = emitPyExpr () "'hello'"
+    builtins.isinstance (pyStrVal, pyStr) |> equal true
+    builtins.isinstance (pyIntVal, pyInt) |> equal true
+
+[<Fact>]
+let ``test isinstance returns false for wrong type`` () =
+    let pyIntVal: obj = emitPyExpr () "42"
+    builtins.isinstance (pyIntVal, pyStr) |> equal false
+
+[<Fact>]
+let ``test type returns type object`` () =
+    let pyStrVal: obj = emitPyExpr () "'hello'"
+    let pyIntVal: obj = emitPyExpr () "42"
+    let t = builtins.``type`` pyStrVal
+    builtins.isinstance (pyStrVal, t) |> equal true
+    builtins.isinstance (pyIntVal, t) |> equal false
+
+[<Fact>]
+let ``test bytes from byte array works`` () =
+    let b = builtins.bytes [| 72uy; 101uy; 108uy; 108uy; 111uy |]
+    builtins.len b |> equal 5
+    b.[0] |> equal 72uy
+    b.[4] |> equal 111uy
+
+[<Fact>]
+let ``test bytes from string with encoding works`` () =
+    let b = builtins.bytes ("ABC", "utf-8")
+    builtins.len b |> equal 3
+    b.[0] |> equal 65uy
+    b.[2] |> equal 67uy