diff --git a/hkmc2/shared/src/main/scala/hkmc2/codegen/FirstClassFunctionTransformer.scala b/hkmc2/shared/src/main/scala/hkmc2/codegen/FirstClassFunctionTransformer.scala
index aad8e08208..c07cb11474 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/codegen/FirstClassFunctionTransformer.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/codegen/FirstClassFunctionTransformer.scala
@@ -38,7 +38,7 @@ class FirstClassFunctionTransformer(using Elaborator.State, Elaborator.Ctx, Rais
   private def getParamList(ts: TermSymbol): Option[ParamList] = ts.defn.flatMap(_.params.headOption)
 
   override def applyPath(p: Path)(k: Path => Block): Block = p match
-    case ref @ Value.Ref(l: BlockMemberSymbol, disamb) => l.tsym match
+    case ref @ Value.Ref(l: BlockMemberSymbol, disamb) => disamb match
       case Some(s: TermSymbol) if s.k is syntax.Fun =>
         val params = getParamList(l).getOrElse(lastWords(s"Cannot get ${l.nme}'s parameter list."))
         val clsDef = generateFCFunctionClass(ref, params)
@@ -46,18 +46,7 @@ class FirstClassFunctionTransformer(using Elaborator.State, Elaborator.Ctx, Rais
         val cls = Value.Ref(clsDef.sym, Some(clsDef.isym))
         Scoped(Set(clsDef.sym, tmp), Define(clsDef, Assign(tmp, Instantiate(false, cls, Nil), k(Value.Ref(tmp, None)))))
       case Some(_) => k(p)
-      case None => disamb match
-          case Some(t: TermSymbol) if t.k is syntax.Fun =>
-            val params = getParamList(l).getOrElse(lastWords(s"Cannot get ${t.nme}'s parameter list."))
-            val clsDef = generateFCFunctionClass(ref, params)
-            val tmp = new TempSymbol(None)
-            val cls = Value.Ref(clsDef.sym, Some(clsDef.isym))
-            Scoped(Set(clsDef.sym, tmp), Define(clsDef, Assign(tmp, Instantiate(false, cls, Nil), k(Value.Ref(tmp, None)))))
-          case Some(_) => k(p)
-          case _ =>
-            raise(ErrorReport(msg"Cannot determine if ${l.nme} is a function." -> ref.toLoc :: Nil,
-              source = Diagnostic.Source.Compilation))
-            k(p)
+      case None => lastWords(s"${l.nme}'s disamb cannot be empty.")
     case sel: Select => sel.symbol match
       case Some(s: TermSymbol) if (s.k is syntax.Fun) =>
         val params = getParamList(s).getOrElse(lastWords(s"Cannot get ${s.nme}'s parameter list."))
@@ -72,6 +61,12 @@ class FirstClassFunctionTransformer(using Elaborator.State, Elaborator.Ctx, Rais
         k(p)
     case _ => k(p)  
 
+  private def pathStartsWith(p: Path, symbol: Local): Bool = p match
+    case Value.Ref(l, _) => l is symbol
+    case Select(p, _) => pathStartsWith(p, symbol)
+    case DynSelect(p, _, _) => pathStartsWith(p, symbol)
+    case _ => false
+
   override def applyResult(r: Result)(k: Result => Block): Block = r match
     case c @ Call(fun, args) => applyArgs(args): args2 =>
       def call(f: Path) = Call(f, args2)(c.isMlsFun, c.mayRaiseEffects, c.explicitTailCall)
@@ -85,7 +80,7 @@ class FirstClassFunctionTransformer(using Elaborator.State, Elaborator.Ctx, Rais
             else k(call(sel.selSN("call")))
           case _ =>
             raise(ErrorReport(msg"Cannot determine if ${sel.name.name} is a function object." -> fun.toLoc :: Nil,
-              source = Diagnostic.Source.Compilation))
+                source = Diagnostic.Source.Compilation))
             k(call(fun))
         case s: DynSelect =>
           raise(ErrorReport(msg"Cannot determine if the dynamic selection is a function object." -> s.toLoc :: Nil,
diff --git a/hkmc2/shared/src/main/scala/hkmc2/codegen/Lowering.scala b/hkmc2/shared/src/main/scala/hkmc2/codegen/Lowering.scala
index b746859612..44527f8d5a 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/codegen/Lowering.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/codegen/Lowering.scala
@@ -134,7 +134,7 @@ class Lowering()(using Config, TL, Raise, State, Ctx):
   )
 
   lazy val unreachableFn =
-    Select(Value.Ref(State.runtimeSymbol), Tree.Ident("unreachable"))(N)
+    Select(Value.Ref(State.runtimeSymbol), Tree.Ident("unreachable"))(S(State.unreachableSymbol))
   
   def unit: Path =
     Select(Value.Ref(State.runtimeSymbol), Tree.Ident("Unit"))(S(State.unitSymbol))
diff --git a/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala b/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala
index 406f36b8a3..5e136ee2d9 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala
@@ -158,6 +158,7 @@ object Elaborator:
       val Str = assumeBuiltinCls("Str")
       val BigInt = assumeBuiltinCls("BigInt")
       val Function = assumeBuiltinCls("Function")
+      val Error = assumeBuiltinCls("Error")
       val Bool = assumeBuiltinCls("Bool")
       val Object = assumeBuiltinCls("Object")
       val Array = assumeBuiltinCls("Array")
@@ -257,6 +258,8 @@ object Elaborator:
     val globalThisSymbol = TopLevelSymbol("globalThis")
     val unitSymbol = ModuleOrObjectSymbol(DummyTypeDef(syntax.Obj), Ident("Unit"))
     val loopEndSymbol = ModuleOrObjectSymbol(DummyTypeDef(syntax.Obj), Ident("LoopEnd"))
+    val tupleSymbol = ModuleOrObjectSymbol(DummyTypeDef(syntax.Mod), Ident("Tuple"))
+    val strSymbol = ModuleOrObjectSymbol(DummyTypeDef(syntax.Mod), Ident("Str"))
     // In JavaScript, `import` can be used for getting current file path, as `import.meta`
     val importSymbol = new VarSymbol(Ident("import"))
     val noSymbol = NoSymbol()
@@ -277,6 +280,14 @@ object Elaborator:
     val nonLocalRet =
       val id = new Ident("ret")
       BlockMemberSymbol(id.name, Nil, true)
+    val unreachableSymbol = TermSymbol(syntax.ImmutVal, N, new Ident("unreachable"))
+    val tupleGetSymbol = createFunSymbolInMod("get", "xs" :: "i" :: Nil, tupleSymbol)
+    val tupleSliceSymbol = createFunSymbolInMod("slice", "xs" :: "i" :: "j" :: Nil, tupleSymbol)
+    val tupleLazySliceSymbol = createFunSymbolInMod("lazySlice", "xs" :: "i" :: "j" :: Nil, tupleSymbol)
+    val strStartsWithSymbol = createFunSymbolInMod("startsWith", "string" :: "prefix" :: Nil, strSymbol)
+    val strGetSymbol = createFunSymbolInMod("get", "string" :: "i" :: Nil, strSymbol)
+    val strTakeSymbol = createFunSymbolInMod("take", "string" :: "n" :: Nil, strSymbol)
+    val strLeaveSymbol = createFunSymbolInMod("leave", "string" :: "n" :: Nil, strSymbol)
     val (matchSuccessClsSymbol, matchSuccessTrmSymbol) =
       val id = new Ident("MatchSuccess")
       val td = TypeDef(syntax.Cls, App(id, Tup(Ident("output") :: Ident("bindings") :: Nil)), N)
@@ -323,6 +334,14 @@ object Elaborator:
     def dbgUid(uid: Uid[Symbol]): Str =
       if dbg then s"‹$uid›" else ""
       // ^ we do not display the uid by default to avoid polluting diff-test outputs
+    // Create a term symbol for a function defined in the given module
+    private def createFunSymbolInMod(name: Str, paramNames: List[Str], mod: ModuleOrObjectSymbol) =
+      val sym = TermSymbol(syntax.Fun, N, Ident(name))
+      val bsym = BlockMemberSymbol(name, Nil, true)
+      val ps = PlainParamList(paramNames.map(s => Param.simple(VarSymbol(Ident(s)))))
+      sym.defn = S(TermDefinition(syntax.Fun, bsym, sym, ps :: Nil, N, N, N,
+        TermDefFlags(true), Modulefulness(S(mod))(false), Nil, N))
+      sym
   transparent inline def State(using state: State): State = state
   
 end Elaborator
diff --git a/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/Normalization.scala b/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/Normalization.scala
index 4b7327ca12..2fbb1f5b19 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/Normalization.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/Normalization.scala
@@ -303,7 +303,7 @@ class Normalization(lowering: Lowering)(using tl: TL)(using Raise, Ctx, State) e
     * match failure in the future.
     */
   private def throwMatchErrorBlock =
-    Throw(Instantiate(mut = false, Select(Value.Ref(State.globalThisSymbol), Tree.Ident("Error"))(N),
+    Throw(Instantiate(mut = false, Select(Value.Ref(State.globalThisSymbol), Tree.Ident("Error"))(S(ctx.builtins.Error)),
         Value.Lit(syntax.Tree.StrLit("match error")).asArg :: Nil)) // TODO add failed-match scrutinee info
   
   import syntax.Keyword.{`if`, `while`}
diff --git a/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/TermSynthesizer.scala b/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/TermSynthesizer.scala
index 79c29c4a99..e52d445a64 100644
--- a/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/TermSynthesizer.scala
+++ b/hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/TermSynthesizer.scala
@@ -56,13 +56,13 @@ trait TermSynthesizer(using State):
     val parameters = parametersOpt.map(_.map(_ -> N))
     FlatPattern.ClassLike(matchFailureClass, State.matchFailureClsSymbol, parameters, false)(Tree.Dummy)
 
-  protected lazy val tupleSlice = sel(sel(runtimeRef, "Tuple"), "slice")
-  protected lazy val tupleLazySlice = sel(sel(runtimeRef, "Tuple"), "lazySlice")
-  protected lazy val tupleGet = sel(sel(runtimeRef, "Tuple"), "get")
-  protected lazy val stringStartsWith = sel(sel(runtimeRef, "Str"), "startsWith")
-  protected lazy val stringGet = sel(sel(runtimeRef, "Str"), "get")
-  protected lazy val stringTake = sel(sel(runtimeRef, "Str"), "take")
-  protected lazy val stringLeave = sel(sel(runtimeRef, "Str"), "leave")
+  protected lazy val tupleSlice = sel(sel(runtimeRef, "Tuple"), "slice", State.tupleSliceSymbol)
+  protected lazy val tupleLazySlice = sel(sel(runtimeRef, "Tuple"), "lazySlice", State.tupleLazySliceSymbol)
+  protected lazy val tupleGet = sel(sel(runtimeRef, "Tuple"), "get", State.tupleGetSymbol)
+  protected lazy val stringStartsWith = sel(sel(runtimeRef, "Str"), "startsWith", State.strStartsWithSymbol)
+  protected lazy val stringGet = sel(sel(runtimeRef, "Str"), "get", State.strGetSymbol)
+  protected lazy val stringTake = sel(sel(runtimeRef, "Str"), "take", State.strTakeSymbol)
+  protected lazy val stringLeave = sel(sel(runtimeRef, "Str"), "leave", State.strLeaveSymbol)
 
   /** Make a term that looks like `runtime.Tuple.get(t, i)`. */
   protected final def callTupleGet(t: Term, i: Int, label: Str): Term =
diff --git a/hkmc2/shared/src/test/mlscript/basics/LazySpreads.mls b/hkmc2/shared/src/test/mlscript/basics/LazySpreads.mls
index c3b1d15ffd..72493744e8 100644
--- a/hkmc2/shared/src/test/mlscript/basics/LazySpreads.mls
+++ b/hkmc2/shared/src/test/mlscript/basics/LazySpreads.mls
@@ -57,7 +57,7 @@ fun sum2 = case
 //│       return 0
 //│     } else if (runtime.Tuple.isArrayLike(caseScrut) && caseScrut.length >= 2) {
 //│       element0$ = runtime.Tuple.get(caseScrut, 0);
-//│       middleElements3 = runtime.safeCall(runtime.Tuple.slice(caseScrut, 1, 1));
+//│       middleElements3 = runtime.Tuple.slice(caseScrut, 1, 1);
 //│       lastElement0$3 = runtime.Tuple.get(caseScrut, -1);
 //│       y = lastElement0$3;
 //│       xs = middleElements3;
diff --git a/hkmc2/shared/src/test/mlscript/bbml/bbCodeGen.mls b/hkmc2/shared/src/test/mlscript/bbml/bbCodeGen.mls
index 8b0b2ecff8..f70a95f52e 100644
--- a/hkmc2/shared/src/test/mlscript/bbml/bbCodeGen.mls
+++ b/hkmc2/shared/src/test/mlscript/bbml/bbCodeGen.mls
@@ -184,7 +184,7 @@ fun nott = case
 //│         return true;
 //│         break;
 //│       default:
-//│         throw globalThis.Object.freeze(new globalThis.Error("match error"));
+//│         throw globalThis.Object.freeze(new globalThis.Error.class("match error"));
 //│         break;
 //│     }
 //│   });
diff --git a/hkmc2/shared/src/test/mlscript/codegen/BlockPrinter.mls b/hkmc2/shared/src/test/mlscript/codegen/BlockPrinter.mls
index c318b93203..818351b102 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/BlockPrinter.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/BlockPrinter.mls
@@ -65,13 +65,13 @@ case
 //│     Array(0) =>
 //│       return Predef.print⁰("empty")
 //│     Array(1+) =>
-//│       set element0$ = runtime⁰.Tuple﹖.get﹖(caseScrut, 0);
-//│       set middleElements = runtime⁰.Tuple﹖.slice﹖(caseScrut, 1, 0);
+//│       set element0$ = runtime⁰.Tuple﹖.get⁰(caseScrut, 0);
+//│       set middleElements = runtime⁰.Tuple﹖.slice⁰(caseScrut, 1, 0);
 //│       set xs = middleElements;
 //│       set x = element0$;
 //│       return Predef.print⁰("non-empty", x)
 //│     else
-//│       throw new globalThis⁰.Error﹖("match error")
+//│       throw new globalThis⁰.Error⁰("match error")
 //│   end
 //│ };
 //│ lambda⁰
diff --git a/hkmc2/shared/src/test/mlscript/codegen/FieldSymbols.mls b/hkmc2/shared/src/test/mlscript/codegen/FieldSymbols.mls
index cf359a6f01..5f639bcb4d 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/FieldSymbols.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/FieldSymbols.mls
@@ -92,7 +92,7 @@ case
 //│       set a = arg$Foo$0$;
 //│       return a
 //│     else
-//│       throw new globalThis⁰.Error﹖("match error")
+//│       throw new globalThis⁰.Error⁰("match error")
 //│   end
 //│ };
 //│ lambda⁰
diff --git a/hkmc2/shared/src/test/mlscript/codegen/FirstClassFunctionTransform.mls b/hkmc2/shared/src/test/mlscript/codegen/FirstClassFunctionTransform.mls
index 62867ee8f2..136b6caaba 100644
--- a/hkmc2/shared/src/test/mlscript/codegen/FirstClassFunctionTransform.mls
+++ b/hkmc2/shared/src/test/mlscript/codegen/FirstClassFunctionTransform.mls
@@ -72,8 +72,8 @@ fun f(x, y, b) =
 //│     this.#b = b;
 //│   }
 //│   #Function$$cap;
-//│   #b;
 //│   #y;
+//│   #b;
 //│   call(z) {
 //│     return lambda1(this.#y, this.#b, z)
 //│   }
@@ -1105,3 +1105,41 @@ foo(print)
 //│ tmp40 = globalThis.Object.freeze(new Function$77());
 //│ foo14(tmp40)
 //│ > 
+
+
+if true is true then print("true")
+//│ > true
+
+
+if 0 is
+  Bool then 1
+  Str then 1
+  0 then 0
+  else 2
+//│ = 0
+  
+
+class Foo(val x)
+
+
+if Foo(1) is
+  Foo(x) then x
+  else 0
+//│ = 1
+
+
+if [1, 2, 3] is
+  [x, y] then x + y
+  [x, y, z] then x + y + z
+  [x, ...y] then x
+  else 0
+//│ = 6
+
+
+class Foo(val x)
+
+let foo = Foo(1) in foo.Foo#x
+//│ = 1
+
+let foo = new Foo(1) in foo.Foo#x
+//│ = 1
diff --git a/hkmc2/shared/src/test/mlscript/lifter/ClassInFun.mls b/hkmc2/shared/src/test/mlscript/lifter/ClassInFun.mls
index 2389dfa158..1c124cf47e 100644
--- a/hkmc2/shared/src/test/mlscript/lifter/ClassInFun.mls
+++ b/hkmc2/shared/src/test/mlscript/lifter/ClassInFun.mls
@@ -138,8 +138,8 @@ f().foo()
 //│     }
 //│   }
 //│   #Good$cap;
-//│   #x;
 //│   #y;
+//│   #x;
 //│   #scope0$cap;
 //│   foo() {
 //│     let tmp6, tmp7;
diff --git a/hkmc2/shared/src/test/mlscript/std/FingerTreeListTest.mls b/hkmc2/shared/src/test/mlscript/std/FingerTreeListTest.mls
index a467226b18..269f79e1f5 100644
--- a/hkmc2/shared/src/test/mlscript/std/FingerTreeListTest.mls
+++ b/hkmc2/shared/src/test/mlscript/std/FingerTreeListTest.mls
@@ -102,7 +102,7 @@ if xs is
 //│ let ls, a, middleElements, element0$;
 //│ if (runtime.Tuple.isArrayLike(xs1) && xs1.length >= 1) {
 //│   element0$ = runtime.Tuple.get(xs1, 0);
-//│   middleElements = runtime.safeCall(runtime.Tuple.slice(xs1, 1, 0));
+//│   middleElements = runtime.Tuple.slice(xs1, 1, 0);
 //│   ls = middleElements;
 //│   a = element0$;
 //│   globalThis.Object.freeze([
diff --git a/hkmc2/shared/src/test/mlscript/ucs/normalization/ExcessiveDeduplication.mls b/hkmc2/shared/src/test/mlscript/ucs/normalization/ExcessiveDeduplication.mls
index 9ab7d29834..82fd273d9b 100644
--- a/hkmc2/shared/src/test/mlscript/ucs/normalization/ExcessiveDeduplication.mls
+++ b/hkmc2/shared/src/test/mlscript/ucs/normalization/ExcessiveDeduplication.mls
@@ -63,14 +63,14 @@ if
 //│ >    x is true and
 //│ >      z is true then 1
 //│ >      y is []=1 and
-//│ >        let tmp:element0$ = ((tmp:runtime.)Tuple.)get(y, 0)
+//│ >        let tmp:element0$ = ((tmp:runtime.)Tuple.)get‹term:get›(y, 0)
 //│ >        let b = tmp:element0$
 //│ >        else
 //│ >          let x
 //│ >          x = 1
 //│ >          builtin:+(x, b)
 //│ >    y is []=1 and
-//│ >      let tmp:element0$ = ((tmp:runtime.)Tuple.)get(y, 0)
+//│ >      let tmp:element0$ = ((tmp:runtime.)Tuple.)get‹term:get›(y, 0)
 //│ >      let b = tmp:element0$
 //│ >      else
 //│ >        let x
diff --git a/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls b/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls
index 33339b6e3a..1e45b57dc4 100644
--- a/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls
+++ b/hkmc2/shared/src/test/mlscript/ucs/patterns/RestTuple.mls
@@ -10,7 +10,7 @@ fun nonsense(xs) = if xs is
 //│ nonsense = function nonsense(xs) {
 //│   let ys, middleElements;
 //│   if (runtime.Tuple.isArrayLike(xs) && xs.length >= 0) {
-//│     middleElements = runtime.safeCall(runtime.Tuple.slice(xs, 0, 0));
+//│     middleElements = runtime.Tuple.slice(xs, 0, 0);
 //│     ys = middleElements;
 //│     return ys
 //│   } else { throw globalThis.Object.freeze(new globalThis.Error("match error")) }
@@ -32,7 +32,7 @@ fun lead_and_last(xs) = if xs is
 //│   let x, ys, y, lastElement0$, middleElements, element0$;
 //│   if (runtime.Tuple.isArrayLike(xs) && xs.length >= 2) {
 //│     element0$ = runtime.Tuple.get(xs, 0);
-//│     middleElements = runtime.safeCall(runtime.Tuple.slice(xs, 1, 1));
+//│     middleElements = runtime.Tuple.slice(xs, 1, 1);
 //│     lastElement0$ = runtime.Tuple.get(xs, -1);
 //│     y = lastElement0$;
 //│     ys = middleElements;
@@ -68,7 +68,7 @@ fun nested_tuple_patterns(xs) = if xs is
 //│     split_default$: {
 //│       if (runtime.Tuple.isArrayLike(xs) && xs.length >= 2) {
 //│         element0$ = runtime.Tuple.get(xs, 0);
-//│         middleElements = runtime.safeCall(runtime.Tuple.slice(xs, 1, 1));
+//│         middleElements = runtime.Tuple.slice(xs, 1, 1);
 //│         lastElement0$ = runtime.Tuple.get(xs, -1);
 //│         if (runtime.Tuple.isArrayLike(middleElements) && middleElements.length === 2) {
 //│           element0$1 = runtime.Tuple.get(middleElements, 0);