diff --git a/core/src/main/scala/org/bykn/bosatsu/ListUtil.scala b/core/src/main/scala/org/bykn/bosatsu/ListUtil.scala
index 950204004..c258dfdb7 100644
--- a/core/src/main/scala/org/bykn/bosatsu/ListUtil.scala
+++ b/core/src/main/scala/org/bykn/bosatsu/ListUtil.scala
@@ -50,4 +50,26 @@ private[bosatsu] object ListUtil {
     if (bs eq as) nel
     else NonEmptyList.fromListUnsafe(bs)
   }
+
+  def distinctByHashSet[A](nel: NonEmptyList[A]): NonEmptyList[A] = {
+    // This code leverages the scala type ::[A] which is the nonempty
+    // list in order to avoid allocations building a NonEmptyList
+    // since a :: tailnel will have to allocate twice vs 1 time.
+    def revCons(item: ::[A], tail: List[A]): NonEmptyList[A] =
+      item.tail match {
+        case nel: ::[A] => revCons(nel, item.head :: tail)
+        case _: Nil.type => NonEmptyList(item.head, tail)
+      }
+    @annotation.tailrec
+    def loop(prior: Set[A], tail: List[A], front: ::[A]): NonEmptyList[A] =
+      tail match {
+        case Nil => revCons(front, Nil)
+        case head :: next =>
+          if (prior(head)) loop(prior, next, front)
+          else loop(prior + head, next, ::(head, front))
+      }
+
+    val h = nel.head
+    loop(Set.empty + h, nel.tail, ::(h, Nil))
+  }
 }
diff --git a/core/src/main/scala/org/bykn/bosatsu/Package.scala b/core/src/main/scala/org/bykn/bosatsu/Package.scala
index aa9604dd1..e7b400702 100644
--- a/core/src/main/scala/org/bykn/bosatsu/Package.scala
+++ b/core/src/main/scala/org/bykn/bosatsu/Package.scala
@@ -248,11 +248,14 @@ object Package {
     // here we make a pass to get all the local names
     val optProg = SourceConverter
       .toProgram(p, imps.map(i => i.copy(pack = i.pack.name)), stmts)
-      .leftMap(
-        _.map(
-          PackageError.SourceConverterErrorIn(_, p): PackageError
-        ).toNonEmptyList
-      )
+      .leftMap { scerrs =>
+        scerrs.groupByNem(_.region)
+          .transform { (region, errs) =>
+            val uniqs = ListUtil.distinctByHashSet(errs.toNonEmptyList)
+            PackageError.SourceConverterErrorsIn(region, uniqs, p): PackageError
+          }
+          .toNonEmptyList
+      }
 
     lazy val typeDefRegions: Map[Type.Const.Defined, Region] =
       stmts.iterator.collect { case tds: TypeDefinitionStatement =>
diff --git a/core/src/main/scala/org/bykn/bosatsu/PackageError.scala b/core/src/main/scala/org/bykn/bosatsu/PackageError.scala
index 2e199e97a..2a9855b80 100644
--- a/core/src/main/scala/org/bykn/bosatsu/PackageError.scala
+++ b/core/src/main/scala/org/bykn/bosatsu/PackageError.scala
@@ -561,8 +561,9 @@ object PackageError {
     }
   }
 
-  case class SourceConverterErrorIn(
-      err: SourceConverter.Error,
+  case class SourceConverterErrorsIn(
+      region: Region,
+      errs: NonEmptyList[SourceConverter.Error],
       pack: PackageName
   ) extends PackageError {
     def message(
@@ -570,16 +571,54 @@ object PackageError {
         errColor: Colorize
     ) = {
       val (lm, _) = sourceMap.getMapSrc(pack)
-      val msg = {
-        val context =
-          lm.showRegion(err.region, 2, errColor)
-            .getOrElse(
-              Doc.str(err.region)
-            ) // we should highlight the whole region
-
-        Doc.text(err.message) + Doc.hardLine + context
+      val context =
+        lm.showRegion(region, 2, errColor)
+          .getOrElse(
+            Doc.str(region)
+          ) // we should highlight the whole region
+      val headDoc = sourceMap.headLine(pack, Some(region))
+
+      val (missing, notMissing) = errs.toList.partitionMap {
+        case ma: SourceConverter.MissingArg => Left(ma)
+        case notMa => Right(notMa)
+      }
+      val mdocs = missing.groupBy { ma => (ma.name, ma.syntax) }
+        .toList
+        .sortBy { case ((name, _), _) => name }
+        .map { case ((_, syn), mas) =>
+          val allMissing = mas.map(_.missing)  
+
+          val missingDoc = Doc.intercalate(Doc.comma + Doc.space,
+            allMissing.sorted.map { m => Doc.text(m.asString) })
+
+          val fieldStr = if (allMissing.lengthCompare(1) == 0) "field" else "fields"
+
+          val hint =
+            syn match {
+              case SourceConverter.ConstructorSyntax.Pat(_) =>
+                Doc.line + Doc.text("if you want to ignore those fields, add a ... to signify ignoring missing.")
+              case _ =>
+                // we can't ignore fields when constructing
+                Doc.empty
+            }
+          (Doc.text(s"missing $fieldStr: ") + missingDoc + Doc.line + Doc.text("in") +
+            Doc.line + syn.toDoc + hint
+          ).nested(4)
+        }
+
+      val mdoc = Doc.intercalate(Doc.hardLine, mdocs)
+      val notMDoc = Doc.intercalate(Doc.hardLine, notMissing.map { se => Doc.text(se.message) })
+      val msg = if (missing.nonEmpty) {
+        if (notMissing.nonEmpty) {
+          mdoc + Doc.hardLine + notMDoc
+        }
+        else mdoc
+      }
+      else {
+        notMDoc
       }
-      val doc = sourceMap.headLine(pack, Some(err.region)) + Doc.hardLine + msg
+
+      val doc = headDoc + Doc.hardLine + msg + Doc.hardLine + context
 
       doc.render(80)
     }
diff --git a/core/src/main/scala/org/bykn/bosatsu/Pattern.scala b/core/src/main/scala/org/bykn/bosatsu/Pattern.scala
index 58178d0aa..76738f5d5 100644
--- a/core/src/main/scala/org/bykn/bosatsu/Pattern.scala
+++ b/core/src/main/scala/org/bykn/bosatsu/Pattern.scala
@@ -870,7 +870,7 @@ object Pattern {
                 }
             )
             prefix +
-              Doc.text(" {") +
+              Doc.text(" { ") +
               kvargs +
               suffix +
               Doc.text(" }")
diff --git a/core/src/test/scala/org/bykn/bosatsu/EvaluationTest.scala b/core/src/test/scala/org/bykn/bosatsu/EvaluationTest.scala
index 2b7316c19..fe57084c3 100644
--- a/core/src/test/scala/org/bykn/bosatsu/EvaluationTest.scala
+++ b/core/src/test/scala/org/bykn/bosatsu/EvaluationTest.scala
@@ -1706,7 +1706,7 @@ x = 1
 
 main = match x:
   case Foo: 2
-""")) { case te @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case te @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       val msg = te.message(Map.empty, Colorize.None)
       assert(!msg.contains("Name("))
       assert(msg.contains("package B\nunknown constructor Foo"))
@@ -1720,7 +1720,7 @@ struct X
 
 main = match 1:
   case X1: 0
-""")) { case te @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case te @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         te.message(
           Map.empty,
@@ -2296,7 +2296,7 @@ get = Pair(first, ...) -> first
 # missing second
 first = 1
 res = get(Pair { first })
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2311,7 +2311,7 @@ get = Pair(first, ...) -> first
 first = 1
 second = 3
 res = get(Pair { first, second, third })
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2323,7 +2323,7 @@ struct Pair(first, second)
 get = Pair { first } -> first
 
 res = get(Pair(1, "two"))
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2336,7 +2336,7 @@ struct Pair(first, second)
 get = Pair(first) -> first
 
 res = get(Pair(1, "two"))
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2349,7 +2349,7 @@ struct Pair(first, second)
 get = \Pair { first, sec: _ } -> first
 
 res = get(Pair(1, "two"))
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2362,7 +2362,7 @@ struct Pair(first, second)
 get = Pair { first, sec: _, ... } -> first
 
 res = get(Pair(1, "two"))
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2375,7 +2375,7 @@ struct Pair(first, second)
 get = Pair(first, _, _) -> first
 
 res = get(Pair(1, "two"))
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
 
@@ -2388,7 +2388,7 @@ struct Pair(first, second)
 get = Pair(first, _, _, ...) -> first
 
 res = get(Pair(1, "two"))
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       s.message(Map.empty, Colorize.None); ()
     }
   }
@@ -2613,7 +2613,7 @@ external def foo(x: String) -> List[String]
 
 def foo(x): x
 
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         s.message(
           Map.empty,
@@ -2630,7 +2630,7 @@ external def foo(x: String) -> List[String]
 
 foo = 1
 
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         s.message(
           Map.empty,
@@ -2646,7 +2646,7 @@ package A
 external def foo(x: String) -> List[String]
 
 external def foo(x: String) -> List[String]
-""")) { case s @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case s @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         s.message(
           Map.empty,
@@ -2686,7 +2686,7 @@ package Err
 struct Foo[a](a)
 
 main = Foo(1, "2")
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -2702,7 +2702,7 @@ package Err
 struct Foo[a](a: a, b: b)
 
 main = Foo(1, "2")
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -2718,7 +2718,7 @@ package Err
 enum Enum[a]: Foo(a)
 
 main = Foo(1, "2")
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -2734,7 +2734,7 @@ package Err
 enum Enum[a]: Foo(a: a), Bar(a: b)
 
 main = Foo(1, "2")
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3004,7 +3004,7 @@ struct Foo
 struct Foo(x)
 
 main = Foo(1)
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3024,7 +3024,7 @@ enum Bar: Foo
 struct Foo(x)
 
 main = Foo(1)
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3132,7 +3132,7 @@ out = match (1,2):
   case (a, a): a
 
 test = Assertion(True, "")
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3149,7 +3149,7 @@ out = match [(1,2), (1, 0)]:
   case _: 0
 
 test = Assertion(True, "")
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3198,7 +3198,7 @@ struct Bar(baz: Either[Int, String])
 
 test = Assertion(True, "")
 
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3287,7 +3287,7 @@ def foo[a](a: a) -> a:
   def and_again[b](x: a): x
   and_again(again(x))
 
-""")) { case sce @ PackageError.SourceConverterErrorIn(_, _) =>
+""")) { case sce @ PackageError.SourceConverterErrorsIn(_, _, _) =>
       assert(
         sce.message(
           Map.empty,
@@ -3870,7 +3870,7 @@ z = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
 
 """
     evalFail(List(testCode)) {
-      case kie @ PackageError.SourceConverterErrorIn(_, _) =>
+      case kie @ PackageError.SourceConverterErrorsIn(_, _, _) =>
         val message = kie.message(Map.empty, Colorize.None)
         assert(
           message.contains(
@@ -3896,7 +3896,7 @@ res = z matches (1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
 
 """
     evalFail(List(testCode1)) {
-      case kie @ PackageError.SourceConverterErrorIn(_, _) =>
+      case kie @ PackageError.SourceConverterErrorsIn(_, _, _) =>
         val message = kie.message(Map.empty, Colorize.None)
         assert(
           message.contains(
diff --git a/core/src/test/scala/org/bykn/bosatsu/ListUtilTest.scala b/core/src/test/scala/org/bykn/bosatsu/ListUtilTest.scala
index 2483438b2..9ce5e60c9 100644
--- a/core/src/test/scala/org/bykn/bosatsu/ListUtilTest.scala
+++ b/core/src/test/scala/org/bykn/bosatsu/ListUtilTest.scala
@@ -94,4 +94,13 @@ class ListUtilTest extends AnyFunSuite {
       }
     }
   }
+
+  test("distinctByHashSet works like List.distinct") {
+   forAll { (nel: NonEmptyList[Byte] ) =>
+     val asList = nel.toList.distinct
+     val viaFn = ListUtil.distinctByHashSet(nel).toList
+
+     assert(viaFn == asList)
+   }
+  }
 }
diff --git a/core/src/test/scala/org/bykn/bosatsu/ParserTest.scala b/core/src/test/scala/org/bykn/bosatsu/ParserTest.scala
index 28e6265dc..4d1929f5d 100644
--- a/core/src/test/scala/org/bykn/bosatsu/ParserTest.scala
+++ b/core/src/test/scala/org/bykn/bosatsu/ParserTest.scala
@@ -28,7 +28,8 @@ trait ParseFns {
       ("...(" + s.drop(idx - 20).take(30) + ")...")
     }
 
-  def firstDiff(s1: String, s2: String): String =
+  @annotation.tailrec
+  final def firstDiff(s1: String, s2: String): String =
     if (s1 == s2) ""
     else if (s1.isEmpty) s2
     else if (s2.isEmpty) s1