diff --git a/sjsonnet/src/sjsonnet/Evaluator.scala b/sjsonnet/src/sjsonnet/Evaluator.scala
index 5855e0f5..2b6bde7f 100644
--- a/sjsonnet/src/sjsonnet/Evaluator.scala
+++ b/sjsonnet/src/sjsonnet/Evaluator.scala
@@ -1,7 +1,7 @@
 package sjsonnet
 
 import sjsonnet.Expr.Member.Visibility
-import sjsonnet.Expr.{Error => _, _}
+import sjsonnet.Expr.{Error as _, *}
 import ujson.Value
 
 import scala.annotation.{switch, tailrec}
@@ -29,7 +29,6 @@ class Evaluator(
   def materialize(v: Val): Value = Materializer.apply(v)
   val cachedImports: collection.mutable.HashMap[Path, Val] =
     collection.mutable.HashMap.empty[Path, Val]
-  var tailstrict: Boolean = false
 
   override def visitExpr(e: Expr)(implicit scope: ValScope): Val = try {
     e match {
@@ -202,49 +201,31 @@ class Evaluator(
     }
   }
 
-  protected def visitApply(e: Apply)(implicit scope: ValScope) = {
+  protected def visitApply(e: Apply)(implicit scope: ValScope): Val = {
     val lhs = visitExpr(e.value)
+    implicit val tailstrictMode: TailstrictMode =
+      if (e.tailstrict) TailstrictModeEnabled else TailstrictModeDisabled
 
-    if (tailstrict) {
+    if (e.tailstrict) {
       lhs.cast[Val.Func].apply(e.args.map(visitExpr(_)), e.namedNames, e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = lhs.cast[Val.Func].apply(e.args.map(visitExpr(_)), e.namedNames, e.pos)
-      tailstrict = false
-      res
     } else {
-      val args = e.args
-      val argsL = new Array[Lazy](args.length)
-      var idx = 0
-      while (idx < args.length) {
-        argsL(idx) = visitAsLazy(args(idx))
-        idx += 1
-      }
-      lhs.cast[Val.Func].apply(argsL, e.namedNames, e.pos)
+      lhs.cast[Val.Func].apply(e.args.map(visitAsLazy(_)), e.namedNames, e.pos)
     }
   }
 
   protected def visitApply0(e: Apply0)(implicit scope: ValScope): Val = {
     val lhs = visitExpr(e.value)
-    if (e.tailstrict) {
-      tailstrict = true
-      val res = lhs.cast[Val.Func].apply0(e.pos)
-      tailstrict = false
-      res
-    } else {
-      lhs.cast[Val.Func].apply0(e.pos)
-    }
+    implicit val tailstrictMode: TailstrictMode =
+      if (e.tailstrict) TailstrictModeEnabled else TailstrictModeDisabled
+    lhs.cast[Val.Func].apply0(e.pos)
   }
 
   protected def visitApply1(e: Apply1)(implicit scope: ValScope): Val = {
     val lhs = visitExpr(e.value)
-    if (tailstrict) {
+    implicit val tailstrictMode: TailstrictMode =
+      if (e.tailstrict) TailstrictModeEnabled else TailstrictModeDisabled
+    if (e.tailstrict) {
       lhs.cast[Val.Func].apply1(visitExpr(e.a1), e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = lhs.cast[Val.Func].apply1(visitExpr(e.a1), e.pos)
-      tailstrict = false
-      res
     } else {
       val l1 = visitAsLazy(e.a1)
       lhs.cast[Val.Func].apply1(l1, e.pos)
@@ -253,13 +234,11 @@ class Evaluator(
 
   protected def visitApply2(e: Apply2)(implicit scope: ValScope): Val = {
     val lhs = visitExpr(e.value)
-    if (tailstrict) {
+    implicit val tailstrictMode: TailstrictMode =
+      if (e.tailstrict) TailstrictModeEnabled else TailstrictModeDisabled
+
+    if (e.tailstrict) {
       lhs.cast[Val.Func].apply2(visitExpr(e.a1), visitExpr(e.a2), e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = lhs.cast[Val.Func].apply2(visitExpr(e.a1), visitExpr(e.a2), e.pos)
-      tailstrict = false
-      res
     } else {
       val l1 = visitAsLazy(e.a1)
       val l2 = visitAsLazy(e.a2)
@@ -269,13 +248,11 @@ class Evaluator(
 
   protected def visitApply3(e: Apply3)(implicit scope: ValScope): Val = {
     val lhs = visitExpr(e.value)
-    if (tailstrict) {
+    implicit val tailstrictMode: TailstrictMode =
+      if (e.tailstrict) TailstrictModeEnabled else TailstrictModeDisabled
+
+    if (e.tailstrict) {
       lhs.cast[Val.Func].apply3(visitExpr(e.a1), visitExpr(e.a2), visitExpr(e.a3), e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = lhs.cast[Val.Func].apply3(visitExpr(e.a1), visitExpr(e.a2), visitExpr(e.a3), e.pos)
-      tailstrict = false
-      res
     } else {
       val l1 = visitAsLazy(e.a1)
       val l2 = visitAsLazy(e.a2)
@@ -284,60 +261,34 @@ class Evaluator(
     }
   }
 
-  protected def visitApplyBuiltin0(e: ApplyBuiltin0) = {
-    if (tailstrict) {
-      e.func.evalRhs(this, e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = e.func.evalRhs(this, e.pos)
-      tailstrict = false
-      res
-    } else {
-      e.func.evalRhs(this, e.pos)
-    }
-  }
+  protected def visitApplyBuiltin0(e: ApplyBuiltin0): Val = e.func.evalRhs(this, e.pos)
 
-  protected def visitApplyBuiltin1(e: ApplyBuiltin1)(implicit scope: ValScope) = {
-    if (tailstrict) {
+  protected def visitApplyBuiltin1(e: ApplyBuiltin1)(implicit scope: ValScope): Val = {
+    if (e.tailstrict) {
       e.func.evalRhs(visitExpr(e.a1), this, e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = e.func.evalRhs(visitExpr(e.a1), this, e.pos)
-      tailstrict = false
-      res
     } else {
       e.func.evalRhs(visitAsLazy(e.a1), this, e.pos)
     }
   }
 
-  protected def visitApplyBuiltin2(e: ApplyBuiltin2)(implicit scope: ValScope) = {
-    if (tailstrict) {
+  protected def visitApplyBuiltin2(e: ApplyBuiltin2)(implicit scope: ValScope): Val = {
+    if (e.tailstrict) {
       e.func.evalRhs(visitExpr(e.a1), visitExpr(e.a2), this, e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = e.func.evalRhs(visitExpr(e.a1), visitExpr(e.a2), this, e.pos)
-      tailstrict = false
-      res
     } else {
       e.func.evalRhs(visitAsLazy(e.a1), visitAsLazy(e.a2), this, e.pos)
     }
   }
 
-  protected def visitApplyBuiltin3(e: ApplyBuiltin3)(implicit scope: ValScope) = {
-    if (tailstrict) {
+  protected def visitApplyBuiltin3(e: ApplyBuiltin3)(implicit scope: ValScope): Val = {
+    if (e.tailstrict) {
       e.func.evalRhs(visitExpr(e.a1), visitExpr(e.a2), visitExpr(e.a3), this, e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = e.func.evalRhs(visitExpr(e.a1), visitExpr(e.a2), visitExpr(e.a3), this, e.pos)
-      tailstrict = false
-      res
     } else {
       e.func.evalRhs(visitAsLazy(e.a1), visitAsLazy(e.a2), visitAsLazy(e.a3), this, e.pos)
     }
   }
 
-  protected def visitApplyBuiltin4(e: ApplyBuiltin4)(implicit scope: ValScope) = {
-    if (tailstrict) {
+  protected def visitApplyBuiltin4(e: ApplyBuiltin4)(implicit scope: ValScope): Val = {
+    if (e.tailstrict) {
       e.func.evalRhs(
         visitExpr(e.a1),
         visitExpr(e.a2),
@@ -346,18 +297,6 @@ class Evaluator(
         this,
         e.pos
       )
-    } else if (e.tailstrict) {
-      tailstrict = true
-      val res = e.func.evalRhs(
-        visitExpr(e.a1),
-        visitExpr(e.a2),
-        visitExpr(e.a3),
-        visitExpr(e.a4),
-        this,
-        e.pos
-      )
-      tailstrict = false
-      res
     } else {
       e.func.evalRhs(
         visitAsLazy(e.a1),
@@ -370,27 +309,17 @@ class Evaluator(
     }
   }
 
-  protected def visitApplyBuiltin(e: ApplyBuiltin)(implicit scope: ValScope) = {
+  protected def visitApplyBuiltin(e: ApplyBuiltin)(implicit scope: ValScope): Val = {
     val arr = new Array[Lazy](e.argExprs.length)
     var idx = 0
 
-    if (tailstrict) {
+    if (e.tailstrict) {
       while (idx < e.argExprs.length) {
         arr(idx) = visitExpr(e.argExprs(idx))
         idx += 1
       }
       e.func.evalRhs(arr, this, e.pos)
-    } else if (e.tailstrict) {
-      tailstrict = true
-      while (idx < e.argExprs.length) {
-        arr(idx) = visitExpr(e.argExprs(idx))
-        idx += 1
-      }
-      val res = e.func.evalRhs(arr, this, e.pos)
-      tailstrict = false
-      res
     } else {
-
       while (idx < e.argExprs.length) {
         val boundIdx = idx
         arr(idx) = visitAsLazy(e.argExprs(boundIdx))
diff --git a/sjsonnet/src/sjsonnet/Interpreter.scala b/sjsonnet/src/sjsonnet/Interpreter.scala
index 94dd9ea4..7acc8c60 100644
--- a/sjsonnet/src/sjsonnet/Interpreter.scala
+++ b/sjsonnet/src/sjsonnet/Interpreter.scala
@@ -197,7 +197,7 @@ class Interpreter(
                 if (tlaExpressions.exists(_ eq expr)) ValScope.empty else vs
               )
             }
-          }.apply0(f.pos)(evaluator)
+          }.apply0(f.pos)(evaluator, TailstrictModeDisabled)
         case x => x
       }
     } yield res
diff --git a/sjsonnet/src/sjsonnet/StaticOptimizer.scala b/sjsonnet/src/sjsonnet/StaticOptimizer.scala
index 3b415bbe..b62b3dca 100644
--- a/sjsonnet/src/sjsonnet/StaticOptimizer.scala
+++ b/sjsonnet/src/sjsonnet/StaticOptimizer.scala
@@ -153,7 +153,8 @@ class StaticOptimizer(
       tailstrict: Boolean): Expr = {
     if (f.staticSafe && args.forall(_.isInstanceOf[Val])) {
       val vargs = args.map(_.asInstanceOf[Val])
-      try f.apply(vargs, null, pos)(ev).asInstanceOf[Expr]
+      val tailstrictMode = if (tailstrict) TailstrictModeEnabled else TailstrictModeDisabled
+      try f.apply(vargs, null, pos)(ev, tailstrictMode).asInstanceOf[Expr]
       catch { case _: Exception => null }
     } else null
   }
diff --git a/sjsonnet/src/sjsonnet/Std.scala b/sjsonnet/src/sjsonnet/Std.scala
index 8a4ac7a2..462f13eb 100644
--- a/sjsonnet/src/sjsonnet/Std.scala
+++ b/sjsonnet/src/sjsonnet/Std.scala
@@ -109,7 +109,7 @@ class Std(
       var res = 0
       if (func.isInstanceOf[Val.Builtin] || func.params.names.length != 1) {
         while (i < a.length) {
-          if (func.apply1(a(i), p)(ev).isInstanceOf[Val.True]) res += 1
+          if (func.apply1(a(i), p)(ev, TailstrictModeDisabled).isInstanceOf[Val.True]) res += 1
           i += 1
         }
       } else {
@@ -231,7 +231,11 @@ class Std(
         arr.asStrictArray.min(ev)
       } else {
         val minTuple = arr.asStrictArray
-          .map(v => keyF.asInstanceOf[Val.Func].apply1(v, pos.fileScope.noOffsetPos)(ev))
+          .map(v =>
+            keyF
+              .asInstanceOf[Val.Func]
+              .apply1(v, pos.fileScope.noOffsetPos)(ev, TailstrictModeDisabled)
+          )
           .zipWithIndex
           .min((x: (Val, Int), y: (Val, Int)) => ev.compare(x._1, y._1))
         arr.force(minTuple._2)
@@ -259,7 +263,11 @@ class Std(
         arr.asStrictArray.max(ev)
       } else {
         val maxTuple = arr.asStrictArray
-          .map(v => keyF.asInstanceOf[Val.Func].apply1(v, pos.fileScope.noOffsetPos)(ev))
+          .map(v =>
+            keyF
+              .asInstanceOf[Val.Func]
+              .apply1(v, pos.fileScope.noOffsetPos)(ev, TailstrictModeDisabled)
+          )
           .zipWithIndex
           .max((x: (Val, Int), y: (Val, Int)) => ev.compare(x._1, y._1))
         arr.force(maxTuple._2)
@@ -296,7 +304,7 @@ class Std(
           var current = init.force
           for (item <- arr.asLazyArray) {
             val c = current
-            current = func.apply2(c, item, pos.noOffset)(ev)
+            current = func.apply2(c, item, pos.noOffset)(ev, TailstrictModeDisabled)
           }
           current
 
@@ -304,7 +312,10 @@ class Std(
           var current = init.force
           for (char <- s.value) {
             val c = current
-            current = func.apply2(c, Val.Str(pos, new String(Array(char))), pos.noOffset)(ev)
+            current = func.apply2(c, Val.Str(pos, new String(Array(char))), pos.noOffset)(
+              ev,
+              TailstrictModeDisabled
+            )
           }
           current
 
@@ -322,14 +333,17 @@ class Std(
           var current = init.force
           for (item <- arr.asLazyArray.reverse) {
             val c = current
-            current = func.apply2(item, c, pos.noOffset)(ev)
+            current = func.apply2(item, c, pos.noOffset)(ev, TailstrictModeDisabled)
           }
           current
         case s: Val.Str =>
           var current = init.force
           for (char <- s.value.reverse) {
             val c = current
-            current = func.apply2(Val.Str(pos, new String(Array(char))), c, pos.noOffset)(ev)
+            current = func.apply2(Val.Str(pos, new String(Array(char))), c, pos.noOffset)(
+              ev,
+              TailstrictModeDisabled
+            )
           }
           current
         case arr => Error.fail("Cannot call foldr on " + arr.prettyName)
@@ -383,12 +397,12 @@ class Std(
       val func = _func.force.asFunc
       if (func.isInstanceOf[Val.Builtin] || func.params.names.length != 1) {
         while (i < a.length) {
-          if (!func.apply1(a(i), p)(ev).isInstanceOf[Val.True]) {
+          if (!func.apply1(a(i), p)(ev, TailstrictModeDisabled).isInstanceOf[Val.True]) {
             var b = new Array[Lazy](a.length - 1)
             System.arraycopy(a, 0, b, 0, i)
             var j = i + 1
             while (j < a.length) {
-              if (func.apply1(a(j), p)(ev).isInstanceOf[Val.True]) {
+              if (func.apply1(a(j), p)(ev, TailstrictModeDisabled).isInstanceOf[Val.True]) {
                 b(i) = a(j)
                 i += 1
               }
@@ -437,7 +451,9 @@ class Std(
       val func = _func.force.asFunc
       Val.Arr(
         pos,
-        arr.force.asArr.asLazyArray.map(v => (() => func.apply1(v, pos.noOffset)(ev)): Lazy)
+        arr.force.asArr.asLazyArray.map(v =>
+          (() => func.apply1(v, pos.noOffset)(ev, TailstrictModeDisabled)): Lazy
+        )
       )
     }
   }
@@ -453,7 +469,10 @@ class Std(
         val k = allKeys(i)
         val v = new Val.Obj.Member(false, Visibility.Normal) {
           def invoke(self: Val.Obj, sup: Val.Obj, fs: FileScope, ev: EvalScope): Val =
-            func.apply2(Val.Str(pos, k), () => obj.value(k, pos.noOffset)(ev), pos.noOffset)(ev)
+            func.apply2(Val.Str(pos, k), () => obj.value(k, pos.noOffset)(ev), pos.noOffset)(
+              ev,
+              TailstrictModeDisabled
+            )
         }
         m.put(k, v)
         i += 1
@@ -472,7 +491,7 @@ class Std(
       while (i < a.length) {
         val x = arr(i)
         val idx = Val.Num(pos, i)
-        a(i) = () => func.apply2(idx, x, pos.noOffset)(ev)
+        a(i) = () => func.apply2(idx, x, pos.noOffset)(ev, TailstrictModeDisabled)
         i += 1
       }
       Val.Arr(pos, a)
@@ -1244,7 +1263,8 @@ class Std(
           var i = 0
           while (i < sz) {
             val forcedI = i
-            a(i) = () => func.apply1(Val.Num(pos, forcedI), pos.noOffset)(ev)
+            a(i) =
+              () => func.apply1(Val.Num(pos, forcedI), pos.noOffset)(ev, TailstrictModeDisabled)
             i += 1
           }
           a
@@ -1349,7 +1369,7 @@ class Std(
         case a: Val.Arr =>
           val arrResults = a.asLazyArray.flatMap { v =>
             {
-              val fres = func.apply1(v, pos.noOffset)(ev)
+              val fres = func.apply1(v, pos.noOffset)(ev, TailstrictModeDisabled)
               fres match {
                 case va: Val.Arr => va.asLazyArray
                 case unknown     => Error.fail("flatMap func must return an array, not " + unknown)
@@ -1361,7 +1381,8 @@ class Std(
         case s: Val.Str =>
           val builder = new StringBuilder()
           for (c: Char <- s.value) {
-            val fres = func.apply1(Val.Str(pos, c.toString), pos.noOffset)(ev)
+            val fres =
+              func.apply1(Val.Str(pos, c.toString), pos.noOffset)(ev, TailstrictModeDisabled)
             builder.append(
               fres match {
                 case fstr: Val.Str => fstr.value
@@ -1387,8 +1408,12 @@ class Std(
           pos,
           arr.asLazyArray.flatMap { i =>
             i.force
-            if (!filter_func.apply1(i, pos.noOffset)(ev).isInstanceOf[Val.True]) None
-            else Some[Lazy](() => map_func.apply1(i, pos.noOffset)(ev))
+            if (
+              !filter_func
+                .apply1(i, pos.noOffset)(ev, TailstrictModeDisabled)
+                .isInstanceOf[Val.True]
+            ) None
+            else Some[Lazy](() => map_func.apply1(i, pos.noOffset)(ev, TailstrictModeDisabled))
           }
         )
     },
@@ -1914,15 +1939,16 @@ class Std(
       arr: mutable.IndexedSeq[? <: Lazy],
       toFind: Val): Boolean = {
     val appliedX = keyF match {
-      case keyFFunc: Val.Func => keyFFunc.apply1(toFind, pos.noOffset)(ev)
+      case keyFFunc: Val.Func => keyFFunc.apply1(toFind, pos.noOffset)(ev, TailstrictModeDisabled)
       case _                  => toFind
     }
     if (ev.settings.strictSetOperations) {
       arr
         .search(appliedX.force)((toFind: Lazy, value: Lazy) => {
           val appliedValue = keyF match {
-            case keyFFunc: Val.Func => keyFFunc.apply1(value, pos.noOffset)(ev)
-            case _                  => value
+            case keyFFunc: Val.Func =>
+              keyFFunc.apply1(value, pos.noOffset)(ev, TailstrictModeDisabled)
+            case _ => value
           }
           ev.compare(toFind.force, appliedValue.force)
         })
@@ -1930,8 +1956,9 @@ class Std(
     } else {
       arr.exists(value => {
         val appliedValue = keyF match {
-          case keyFFunc: Val.Func => keyFFunc.apply1(value, pos.noOffset)(ev)
-          case _                  => value
+          case keyFFunc: Val.Func =>
+            keyFFunc.apply1(value, pos.noOffset)(ev, TailstrictModeDisabled)
+          case _ => value
         }
         ev.equal(appliedValue.force, appliedX.force)
       })
@@ -1980,8 +2007,8 @@ class Std(
         }
       } else if (!keyF.isInstanceOf[Val.False]) {
         val keyFFunc = keyF.asInstanceOf[Val.Func]
-        val o1Key = keyFFunc.apply1(v, pos.noOffset)(ev)
-        val o2Key = keyFFunc.apply1(out.last, pos.noOffset)(ev)
+        val o1Key = keyFFunc.apply1(v, pos.noOffset)(ev, TailstrictModeDisabled)
+        val o2Key = keyFFunc.apply1(out.last, pos.noOffset)(ev, TailstrictModeDisabled)
         if (!ev.equal(o1Key, o2Key)) {
           out.append(v)
         }
@@ -2001,7 +2028,9 @@ class Std(
       Val.Arr(
         pos,
         if (keyFFunc != null) {
-          val keys: Array[Val] = vs.map(v => keyFFunc(Array(v.force), null, pos.noOffset)(ev).force)
+          val keys: Array[Val] = vs.map(v =>
+            keyFFunc(Array(v.force), null, pos.noOffset)(ev, TailstrictModeDisabled).force
+          )
           val keyType = keys(0).getClass
           if (classOf[Val.Bool].isAssignableFrom(keyType)) {
             Error.fail("Cannot sort with key values that are booleans")
diff --git a/sjsonnet/src/sjsonnet/Val.scala b/sjsonnet/src/sjsonnet/Val.scala
index 3385bd02..acc6b573 100644
--- a/sjsonnet/src/sjsonnet/Val.scala
+++ b/sjsonnet/src/sjsonnet/Val.scala
@@ -1,7 +1,6 @@
 package sjsonnet
 
 import java.util
-import java.util.Arrays
 import sjsonnet.Expr.Member.Visibility
 import sjsonnet.Expr.Params
 
@@ -16,7 +15,7 @@ import scala.reflect.ClassTag
  * on-demand
  */
 abstract class Lazy {
-  protected var cached: Val = null
+  protected var cached: Val = _
   def compute(): Val
   final def force: Val = {
     if (cached == null) cached = compute()
@@ -231,7 +230,7 @@ object Val {
       with Expr.ObjBody {
     var asserting: Boolean = false
 
-    def getSuper = `super`
+    def getSuper: Obj = `super`
 
     private def getValue0: util.LinkedHashMap[String, Obj.Member] = {
       // value0 is always defined for non-static objects, so if we're computing it here
@@ -354,27 +353,23 @@ object Val {
      * Merge two values for "nested field inheritance"; see
      * https://jsonnet.org/ref/language.html#nested-field-inheritance for background.
      */
-    def mergeMember(l: Val, r: Val, pos: Position)(implicit evaluator: EvalScope): Literal = {
-      val lStr = l.isInstanceOf[Val.Str]
-      val rStr = r.isInstanceOf[Val.Str]
-      if (lStr || rStr) {
-        val ll = if (lStr) l.asInstanceOf[Val.Str].value else renderString(l)
-        val rr = if (rStr) r.asInstanceOf[Val.Str].value else renderString(r)
-        Val.Str(pos, ll ++ rr)
-      } else if (l.isInstanceOf[Val.Num] && r.isInstanceOf[Val.Num]) {
-        val ll = l.asInstanceOf[Val.Num].value
-        val rr = r.asInstanceOf[Val.Num].value
-        Val.Num(pos, ll + rr)
-      } else if (l.isInstanceOf[Val.Arr] && r.isInstanceOf[Val.Arr]) {
-        val ll = l.asInstanceOf[Val.Arr].asLazyArray
-        val rr = r.asInstanceOf[Val.Arr].asLazyArray
-        Val.Arr(pos, ll ++ rr)
-      } else if (l.isInstanceOf[Val.Obj] && r.isInstanceOf[Val.Obj]) {
-        val ll = l.asInstanceOf[Val.Obj]
-        val rr = r.asInstanceOf[Val.Obj]
-        rr.addSuper(pos, ll)
-      } else throw new MatchError((l, r))
-    }
+    private def mergeMember(l: Val, r: Val, pos: Position)(implicit evaluator: EvalScope): Literal =
+      (l, r) match {
+        case (lStr: Val.Str, rStr: Val.Str) =>
+          Val.Str(pos, lStr.value ++ rStr.value)
+        case (lStr: Val.Str, _) =>
+          Val.Str(pos, lStr.value ++ renderString(r))
+        case (_, rStr: Val.Str) =>
+          Val.Str(pos, renderString(l) ++ rStr.value)
+        case (lNum: Val.Num, rNum: Val.Num) =>
+          Val.Num(pos, lNum.value + rNum.value)
+        case (lArr: Val.Arr, rArr: Val.Arr) =>
+          Val.Arr(pos, lArr.asLazyArray ++ rArr.asLazyArray)
+        case (lObj: Val.Obj, rObj: Val.Obj) =>
+          rObj.addSuper(pos, lObj)
+        case _ =>
+          throw new MatchError((l, r))
+      }
 
     def valueRaw(
         k: String,
@@ -418,7 +413,7 @@ object Val {
   final class StaticObjectFieldSet(protected val keys: Array[String]) {
 
     override def hashCode(): Int = {
-      Arrays.hashCode(keys.asInstanceOf[Array[Object]])
+      util.Arrays.hashCode(keys.asInstanceOf[Array[Object]])
     }
 
     override def equals(obj: scala.Any): Boolean = {
@@ -451,7 +446,7 @@ object Val {
         idx += 1
       case other =>
         throw new Error(
-          s"Unexpected non-literal field in static object: ${other} of class ${other.getClass}"
+          s"Unexpected non-literal field in static object: $other of class ${other.getClass}"
         )
     }
     val fieldSet = new StaticObjectFieldSet(keys)
@@ -482,15 +477,16 @@ object Val {
     override def asFunc: Func = this
 
     def apply(argsL: Array[? <: Lazy], namedNames: Array[String], outerPos: Position)(implicit
-        ev: EvalScope): Val = {
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val = {
       val simple = namedNames == null && params.names.length == argsL.length
       val funDefFileScope: FileScope = pos match {
         case null => outerPos.fileScope
         case p    => p.fileScope
       }
       // println(s"apply: argsL: ${argsL.length}, namedNames: $namedNames, paramNames: ${params.names.mkString(",")}")
-      if (simple || ev.tailstrict) {
-        if (ev.tailstrict) {
+      if (simple || tailstrictMode == TailstrictModeEnabled) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argsL.foreach(_.force)
         }
         val newScope = defSiteValScope.extendSimple(argsL)
@@ -547,13 +543,12 @@ object Val {
               outerPos
             )
           }
-          // println(argVals.mkString(s"params: ${params.names.length}, argsL: ${argsL.length}, argVals: [", ", ", "]"))
         }
         evalRhs(newScope, ev, funDefFileScope, outerPos)
       }
     }
 
-    def apply0(outerPos: Position)(implicit ev: EvalScope): Val = {
+    def apply0(outerPos: Position)(implicit ev: EvalScope, tailstrictMode: TailstrictMode): Val = {
       if (params.names.length != 0) apply(Evaluator.emptyLazyArray, null, outerPos)
       else {
         val funDefFileScope: FileScope = pos match {
@@ -564,14 +559,16 @@ object Val {
       }
     }
 
-    def apply1(argVal: Lazy, outerPos: Position)(implicit ev: EvalScope): Val = {
+    def apply1(argVal: Lazy, outerPos: Position)(implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val = {
       if (params.names.length != 1) apply(Array(argVal), null, outerPos)
       else {
         val funDefFileScope: FileScope = pos match {
           case null => outerPos.fileScope
           case p    => p.fileScope
         }
-        if (ev.tailstrict) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argVal.force
         }
         val newScope: ValScope = defSiteValScope.extendSimple(argVal)
@@ -579,14 +576,16 @@ object Val {
       }
     }
 
-    def apply2(argVal1: Lazy, argVal2: Lazy, outerPos: Position)(implicit ev: EvalScope): Val = {
+    def apply2(argVal1: Lazy, argVal2: Lazy, outerPos: Position)(implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val = {
       if (params.names.length != 2) apply(Array(argVal1, argVal2), null, outerPos)
       else {
         val funDefFileScope: FileScope = pos match {
           case null => outerPos.fileScope
           case p    => p.fileScope
         }
-        if (ev.tailstrict) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argVal1.force
           argVal2.force
         }
@@ -596,14 +595,15 @@ object Val {
     }
 
     def apply3(argVal1: Lazy, argVal2: Lazy, argVal3: Lazy, outerPos: Position)(implicit
-        ev: EvalScope): Val = {
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val = {
       if (params.names.length != 3) apply(Array(argVal1, argVal2, argVal3), null, outerPos)
       else {
         val funDefFileScope: FileScope = pos match {
           case null => outerPos.fileScope
           case p    => p.fileScope
         }
-        if (ev.tailstrict) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argVal1.force
           argVal2.force
           argVal3.force
@@ -638,20 +638,23 @@ object Val {
 
     def evalRhs(args: Array[? <: Lazy], ev: EvalScope, pos: Position): Val
 
-    override def apply1(argVal: Lazy, outerPos: Position)(implicit ev: EvalScope): Val =
+    override def apply1(argVal: Lazy, outerPos: Position)(implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (params.names.length != 1) apply(Array(argVal), null, outerPos)
       else {
-        if (ev.tailstrict) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argVal.force
         }
         evalRhs(Array(argVal), ev, outerPos)
       }
 
     override def apply2(argVal1: Lazy, argVal2: Lazy, outerPos: Position)(implicit
-        ev: EvalScope): Val =
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (params.names.length != 2) apply(Array(argVal1, argVal2), null, outerPos)
       else {
-        if (ev.tailstrict) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argVal1.force
           argVal2.force
         }
@@ -659,10 +662,11 @@ object Val {
       }
 
     override def apply3(argVal1: Lazy, argVal2: Lazy, argVal3: Lazy, outerPos: Position)(implicit
-        ev: EvalScope): Val =
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (params.names.length != 3) apply(Array(argVal1, argVal2, argVal3), null, outerPos)
       else {
-        if (ev.tailstrict) {
+        if (tailstrictMode == TailstrictModeEnabled) {
           argVal1.force
           argVal2.force
           argVal3.force
@@ -692,7 +696,9 @@ object Val {
     def evalRhs(ev: EvalScope, pos: Position): Val
 
     override def apply(argVals: Array[? <: Lazy], namedNames: Array[String], outerPos: Position)(
-        implicit ev: EvalScope): Val =
+        implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (namedNames == null && argVals.length == 0)
         evalRhs(ev, outerPos)
       else super.apply(argVals, namedNames, outerPos)
@@ -706,7 +712,9 @@ object Val {
     def evalRhs(arg1: Lazy, ev: EvalScope, pos: Position): Val
 
     override def apply(argVals: Array[? <: Lazy], namedNames: Array[String], outerPos: Position)(
-        implicit ev: EvalScope): Val =
+        implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (namedNames == null && argVals.length == 1) evalRhs(argVals(0).force, ev, outerPos)
       else super.apply(argVals, namedNames, outerPos)
   }
@@ -719,13 +727,16 @@ object Val {
     def evalRhs(arg1: Lazy, arg2: Lazy, ev: EvalScope, pos: Position): Val
 
     override def apply(argVals: Array[? <: Lazy], namedNames: Array[String], outerPos: Position)(
-        implicit ev: EvalScope): Val =
+        implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (namedNames == null && argVals.length == 2)
         evalRhs(argVals(0).force, argVals(1).force, ev, outerPos)
       else super.apply(argVals, namedNames, outerPos)
 
     override def apply2(argVal1: Lazy, argVal2: Lazy, outerPos: Position)(implicit
-        ev: EvalScope): Val =
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (params.names.length == 2) evalRhs(argVal1.force, argVal2.force, ev, outerPos)
       else super.apply(Array(argVal1, argVal2), null, outerPos)
   }
@@ -743,7 +754,9 @@ object Val {
     def evalRhs(arg1: Lazy, arg2: Lazy, arg3: Lazy, ev: EvalScope, pos: Position): Val
 
     override def apply(argVals: Array[? <: Lazy], namedNames: Array[String], outerPos: Position)(
-        implicit ev: EvalScope): Val =
+        implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (namedNames == null && argVals.length == 3)
         evalRhs(argVals(0).force, argVals(1).force, argVals(2).force, ev, outerPos)
       else super.apply(argVals, namedNames, outerPos)
@@ -763,7 +776,9 @@ object Val {
     def evalRhs(arg1: Lazy, arg2: Lazy, arg3: Lazy, arg4: Lazy, ev: EvalScope, pos: Position): Val
 
     override def apply(argVals: Array[? <: Lazy], namedNames: Array[String], outerPos: Position)(
-        implicit ev: EvalScope): Val =
+        implicit
+        ev: EvalScope,
+        tailstrictMode: TailstrictMode): Val =
       if (namedNames == null && argVals.length == 4)
         evalRhs(
           argVals(0).force,
@@ -777,13 +792,15 @@ object Val {
   }
 }
 
+sealed trait TailstrictMode
+case object TailstrictModeEnabled extends TailstrictMode
+case object TailstrictModeDisabled extends TailstrictMode
+
 /**
  * [[EvalScope]] models the per-evaluator context that is propagated throughout the Jsonnet
  * evaluation.
  */
 abstract class EvalScope extends EvalErrorScope with Ordering[Val] {
-  def tailstrict: Boolean
-
   def visitExpr(expr: Expr)(implicit scope: ValScope): Val
 
   def materialize(v: Val): ujson.Value
@@ -792,7 +809,7 @@ abstract class EvalScope extends EvalErrorScope with Ordering[Val] {
 
   def compare(x: Val, y: Val): Int
 
-  val emptyMaterializeFileScope = new FileScope(wd / "(materialize)")
+  private val emptyMaterializeFileScope = new FileScope(wd / "(materialize)")
   val emptyMaterializeFileScopePos = new Position(emptyMaterializeFileScope, -1)
 
   def settings: Settings
diff --git a/sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet b/sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet
new file mode 100644
index 00000000..e201b958
--- /dev/null
+++ b/sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet
@@ -0,0 +1,20 @@
+local helper = {
+  local this = self,
+
+  bar(param, auxone=0, auxtwo=0)::
+    param + auxone + auxtwo,
+
+  foo(param)::
+    local sum_from_one_to_n(counter, n) =
+      if n == 0 then
+        error "n is 0"
+      else
+        sum_from_one_to_n(this.bar(counter + n, auxtwo=1), n - 1) tailstrict;
+
+    local result = sum_from_one_to_n(0, param);
+    result,
+};
+
+{
+  bar: helper.foo(10),
+}
diff --git a/sjsonnet/test/resources/test_suite/tailstrict_eager_params.jsonnet b/sjsonnet/test/resources/test_suite/tailstrict_eager_params.jsonnet
new file mode 100644
index 00000000..d0f19079
--- /dev/null
+++ b/sjsonnet/test/resources/test_suite/tailstrict_eager_params.jsonnet
@@ -0,0 +1,20 @@
+local helper = {
+  local this = self,
+
+  bar(param, unusedParam)::
+    param,
+
+  foo(param)::
+    local sum_from_one_to_n(counter, n) =
+      if n == 0 then
+        counter
+      else
+        sum_from_one_to_n(this.bar(counter + n, error 'Kaboom!'), n - 1) tailstrict;
+
+    local result = sum_from_one_to_n(0, param);
+    result,
+};
+
+{
+  bar: helper.foo(10),
+}
diff --git a/sjsonnet/test/resources/test_suite/tailstrict_eager_params.jsonnet.golden b/sjsonnet/test/resources/test_suite/tailstrict_eager_params.jsonnet.golden
new file mode 100644
index 00000000..01e2a814
--- /dev/null
+++ b/sjsonnet/test/resources/test_suite/tailstrict_eager_params.jsonnet.golden
@@ -0,0 +1,3 @@
+{
+   "bar": 55
+}
\ No newline at end of file
diff --git a/sjsonnet/test/resources/test_suite/tailstrict_missing_bindings.jsonnet b/sjsonnet/test/resources/test_suite/tailstrict_missing_bindings.jsonnet
new file mode 100644
index 00000000..86744134
--- /dev/null
+++ b/sjsonnet/test/resources/test_suite/tailstrict_missing_bindings.jsonnet
@@ -0,0 +1,20 @@
+local helper = {
+  local this = self,
+
+  bar(param, auxone=0, auxtwo=0)::
+    param + auxone + auxtwo,
+
+  foo(param)::
+    local sum_from_one_to_n(counter, n) =
+      if n == 0 then
+        counter
+      else
+        sum_from_one_to_n(this.bar(counter + n, auxtwo=1), n - 1) tailstrict;
+
+    local result = sum_from_one_to_n(0, param);
+    result,
+};
+
+{
+  bar: helper.foo(10),
+}
diff --git a/sjsonnet/test/resources/test_suite/tailstrict_missing_bindings.jsonnet.golden b/sjsonnet/test/resources/test_suite/tailstrict_missing_bindings.jsonnet.golden
new file mode 100644
index 00000000..2c420752
--- /dev/null
+++ b/sjsonnet/test/resources/test_suite/tailstrict_missing_bindings.jsonnet.golden
@@ -0,0 +1,3 @@
+{
+   "bar": 65
+}
\ No newline at end of file
diff --git a/sjsonnet/test/src-js/sjsonnet/ErrorTests.scala b/sjsonnet/test/src-js/sjsonnet/ErrorTests.scala
index 71e727ad..24bd4ea0 100644
--- a/sjsonnet/test/src-js/sjsonnet/ErrorTests.scala
+++ b/sjsonnet/test/src-js/sjsonnet/ErrorTests.scala
@@ -312,6 +312,16 @@ object ErrorTests extends TestSuite {
       suite = "imports"
     )
 
+    test("tailstrict_stack") - check(
+      """|sjsonnet.Error: n is 0
+         |    at [Error].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:10:9)
+         |    at [Apply2].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:12:26)
+         |    at [Apply2].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:14:37)
+         |    at [ValidId result].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:15:5)
+         |    at [Apply1].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:19:18)
+         |""".stripMargin
+    )
+
     test("too_many_arg") - check(
       """|sjsonnet.Error: Too many args, function has 2 parameter(s)
          |    at [Apply].(sjsonnet/test/resources/imports/error.too_many_arg.jsonnet:3:6)
diff --git a/sjsonnet/test/src-js/sjsonnet/FileTests.scala b/sjsonnet/test/src-js/sjsonnet/FileTests.scala
index 4cc3bce7..a2dad413 100644
--- a/sjsonnet/test/src-js/sjsonnet/FileTests.scala
+++ b/sjsonnet/test/src-js/sjsonnet/FileTests.scala
@@ -107,6 +107,8 @@ object FileTests extends TestSuite {
     test("slice.sugar") - check()
     test("std_all_hidden") - check()
     test("stdlib_native") - check()
+    test("tailstrict_eager_params") - checkGolden()
+    test("tailstrict_missing_bindings") - checkGolden()
     test("text_block") - check()
     test("tla.simple") - check()
     test("unicode") - check()
diff --git a/sjsonnet/test/src-jvm-native/ErrorTests.scala b/sjsonnet/test/src-jvm-native/ErrorTests.scala
index 37e3a6fd..dc7fe4ed 100644
--- a/sjsonnet/test/src-jvm-native/ErrorTests.scala
+++ b/sjsonnet/test/src-jvm-native/ErrorTests.scala
@@ -299,6 +299,16 @@ object ErrorTests extends TestSuite {
       suite = "imports"
     )
 
+    test("tailstrict_stack") - check(
+      """|sjsonnet.Error: n is 0
+         |    at [Error].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:10:9)
+         |    at [Apply2].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:12:26)
+         |    at [Apply2].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:14:37)
+         |    at [ValidId result].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:15:5)
+         |    at [Apply1].(sjsonnet/test/resources/test_suite/error.tailstrict_stack.jsonnet:19:18)
+         |""".stripMargin
+    )
+
     test("too_many_arg") - check(
       """|sjsonnet.Error: Too many args, function has 2 parameter(s)
          |    at [Apply].(sjsonnet/test/resources/imports/error.too_many_arg.jsonnet:3:6)
diff --git a/sjsonnet/test/src-jvm/sjsonnet/FileTests.scala b/sjsonnet/test/src-jvm/sjsonnet/FileTests.scala
index 720b7004..8f2ba7ce 100644
--- a/sjsonnet/test/src-jvm/sjsonnet/FileTests.scala
+++ b/sjsonnet/test/src-jvm/sjsonnet/FileTests.scala
@@ -74,6 +74,8 @@ object FileTests extends TestSuite {
     "slice.sugar" - check()
     test("std_all_hidden") - check()
     test("stdlib") - check()
+    test("tailstrict_eager_params") - checkGolden()
+    test("tailstrict_missing_bindings") - checkGolden()
     test("text_block") - check()
     "tla.simple" - check()
     test("unicode") - check()
diff --git a/sjsonnet/test/src-native/sjsonnet/FileTests.scala b/sjsonnet/test/src-native/sjsonnet/FileTests.scala
index 54870978..61d35054 100644
--- a/sjsonnet/test/src-native/sjsonnet/FileTests.scala
+++ b/sjsonnet/test/src-native/sjsonnet/FileTests.scala
@@ -61,7 +61,7 @@ object FileTests extends TestSuite {
     test("oop_extra") - check()
     test("parsing_edge_cases") - check()
     test("precedence") - check()
-    test("recursive_function_native") - check()
+    test("recursive_function") - check()
     test("recursive_import_ok") - check()
     test("recursive_object") - check()
     test("regex") - check()
@@ -72,6 +72,8 @@ object FileTests extends TestSuite {
     "slice.sugar" - check()
     test("std_all_hidden") - check()
     test("stdlib_native") - check()
+    test("tailstrict_eager_params") - checkGolden()
+    test("tailstrict_missing_bindings") - checkGolden()
     test("text_block") - check()
     "tla.simple" - check()
     test("unicode") - check()
diff --git a/sjsonnet/test/src/sjsonnet/FormatTests.scala b/sjsonnet/test/src/sjsonnet/FormatTests.scala
index 3238b0d4..6b227901 100644
--- a/sjsonnet/test/src/sjsonnet/FormatTests.scala
+++ b/sjsonnet/test/src/sjsonnet/FormatTests.scala
@@ -10,7 +10,6 @@ object FormatTests extends TestSuite {
     val json = ujson.read(jsonStr)
     val formatted = Format.format(fmt, Materializer.reverse(null, json), dummyPos)(
       new EvalScope {
-        def tailstrict: Boolean = false
         def extVars: String => Option[sjsonnet.Expr] = _ => None
         def wd: Path = DummyPath()
         def visitExpr(expr: Expr)(implicit scope: ValScope): Val = ???