The latest state of expr_parser

Node.scala

@@ -385,7 +385,7 @@ object Node:
 
       require(
         results.size == 1,
-        s"token(s) not found ${(tok +: toks).map(_.name).mkString(", ")}"
+        s"token(s) not found ${(tok +: toks).map(_.name).mkString(", ")}, in ${this.toShortString()}"
       )
       results.head
 

PassSeq.scala

@@ -21,15 +21,16 @@ import dsl.*
 transparent trait PassSeq:
   def inputWellformed: Wellformed
   final def outputWellformed: Wellformed =
-    assert(entriesSealed)
+    allPasses // compute allPasses, needed to enforce complete initialization
     entries.last.wellformed
 
   private val entries = mutable.ListBuffer.empty[PassSeq.Entry]
   private var entriesSealed = false
 
   protected def prevWellformed(using BuildCtx): Wellformed =
-    require(entries.nonEmpty, "there is no previous Wellformed")
-    entries.last.wellformed
+    if entries.isEmpty
+    then inputWellformed
+    else entries.last.wellformed
 
   protected object wellformed:
     def :=(using ctx: BuildCtx)(wellformed: Wellformed): Unit =

Wellformed.scala

@@ -524,6 +524,15 @@ object Wellformed:
               s"$token's shape is not appropriate for adding cases ($shape)"
             )
 
+      def deleteShape(): Unit =
+        token match
+          case Node.Top =>
+            require(topShapeOpt.nonEmpty)
+            topShapeOpt = None
+          case token: Token =>
+            require(assigns.contains(token))
+            assigns.remove(token)
+
       def importFrom(wf2: Wellformed): Unit =
         def fillFromShape(shape: Shape): Unit =
           shape match
@@ -550,6 +559,7 @@ object Wellformed:
             topShapeOpt = Some(wf2.topShape)
             fillFromShape(wf2.topShape)
           case token: Token => fillFromTokenOrEmbed(token)
+      end importFrom
 
     private[Wellformed] def build(): Wellformed =
       require(topShapeOpt.nonEmpty)