diff --git a/common/parser-service/src/main/scala/org/enso/ParserService.scala b/common/parser-service/src/main/scala/org/enso/ParserService.scala
index 6d1a26b1e06..bee20f43d62 100644
--- a/common/parser-service/src/main/scala/org/enso/ParserService.scala
+++ b/common/parser-service/src/main/scala/org/enso/ParserService.scala
@@ -36,13 +36,13 @@ case class ParserService() extends Server with Protocol {
 
   def serializeAst(ast: AST.Module): String = ast.toJson().noSpaces
 
-  def runParser(program: String, ids: Seq[((Int, Int), AST.ID)]): AST.Module =
-    new Parser().run(new Reader(program), Parser.idMap(ids))
+  def runParser(program: String, ids: Parser.IDMap): AST.Module =
+    new Parser().run(new Reader(program), ids)
 
   def handleRequest(request: Request): Response = {
     request match {
       case ParseRequest(program, idsJson) =>
-        val ids = decode[Seq[((Int, Int), AST.ID)]](idsJson).getOrElse {
+        val ids = Parser.idMapFromJson(idsJson).getOrElse {
           throw new Exception("Could not decode IDMap from json.")
         }
         val ast  = runParser(program, ids)
diff --git a/common/syntax/definition/src/main/scala/org/enso/data/Index.scala b/common/syntax/definition/src/main/scala/org/enso/data/Index.scala
index cbee2685809..2783f1b737c 100644
--- a/common/syntax/definition/src/main/scala/org/enso/data/Index.scala
+++ b/common/syntax/definition/src/main/scala/org/enso/data/Index.scala
@@ -1,18 +1,18 @@
 package org.enso.data
 
 /** Strongly typed index position in a container. */
-case class Index(index: Int) extends AnyVal with Ordered[Index] {
-  def +(offset: Size): Index = Index(index + offset.value)
-  def -(offset: Size): Index = Index(index - offset.value)
+case class Index(value: Int) extends AnyVal with Ordered[Index] {
+  def +(offset: Size): Index = Index(value + offset.value)
+  def -(offset: Size): Index = Index(value - offset.value)
 
   /** Span between two text positions. Operands order is irrelevant. */
   def <->(that: Index): Span =
-    if (index <= that.index) Span(this, Size(that.index - index))
-    else Span(that, Size(index - that.index))
+    if (value <= that.value) Span(this, Size(that.value - value))
+    else Span(that, Size(value - that.value))
 
-  def asSize: Size = Size(index)
+  def asSize: Size = Size(value)
 
-  def compare(rhs: Index): Int = index compare rhs.index
+  def compare(rhs: Index): Int = value compare rhs.value
 }
 
 object Index {
diff --git a/common/syntax/definition/src/main/scala/org/enso/data/Span.scala b/common/syntax/definition/src/main/scala/org/enso/data/Span.scala
index 43bcc6e7650..397f586092b 100644
--- a/common/syntax/definition/src/main/scala/org/enso/data/Span.scala
+++ b/common/syntax/definition/src/main/scala/org/enso/data/Span.scala
@@ -3,13 +3,13 @@ package org.enso.data
 import org.enso.syntax.text.AST
 
 /** Strongly typed span in a container. */
-case class Span(begin: Index, length: Size) extends Ordered[Span] {
+case class Span(index: Index, size: Size) extends Ordered[Span] {
 
   override def compare(that: Span): Int =
-    (begin -> that.length).compare(that.begin -> length)
+    (index -> that.size).compare(that.index -> size)
 
   /** Index of the first element past the span */
-  def end: Index = begin + length
+  def end: Index = index + size
 
 }
 
@@ -25,6 +25,6 @@ object Span {
 
   implicit class StringOps(text: String) {
     def substring(span: Span): String =
-      text.substring(span.begin.index, span.end.index)
+      text.substring(span.index.value, span.end.value)
   }
 }
diff --git a/common/syntax/specialization/js/src/main/scala/org/enso/syntax/text/Main.scala b/common/syntax/specialization/js/src/main/scala/org/enso/syntax/text/Main.scala
index 5f621b03c81..4dda902ed3f 100644
--- a/common/syntax/specialization/js/src/main/scala/org/enso/syntax/text/Main.scala
+++ b/common/syntax/specialization/js/src/main/scala/org/enso/syntax/text/Main.scala
@@ -1,9 +1,7 @@
 package org.enso.syntax.text
 
 import org.enso.flexer.Reader
-import org.enso.syntax.text
 
-import io.circe.parser._
 import scala.scalajs.js.annotation._
 import scala.scalajs.js
 
@@ -11,11 +9,10 @@ object Parse {
   @JSExportTopLevel("parse")
   def parse(program: String, idsJson: String): String = {
     try {
-      val ids = decode[Seq[((Int, Int), AST.ID)]](idsJson).getOrElse {
+      val ids = Parser.idMapFromJson(idsJson).getOrElse {
         throw new Exception("Could not decode IDMap from json.")
       }
-      val ast = new text.Parser().run(new Reader(program), text.Parser.idMap(ids))
-      ast.toJson().noSpacesSortKeys
+      new Parser().run(new Reader(program), ids).toJson().noSpacesSortKeys
     } catch {
       // FIXME We wrap the error message in JavaScriptException, so that javascript
       //  can display it. This is no longer needed in scalajs 1.0
diff --git a/common/syntax/specialization/shared/src/main/scala/org/enso/syntax/text/Parser.scala b/common/syntax/specialization/shared/src/main/scala/org/enso/syntax/text/Parser.scala
index 0dbd014a356..538eb5be39c 100644
--- a/common/syntax/specialization/shared/src/main/scala/org/enso/syntax/text/Parser.scala
+++ b/common/syntax/specialization/shared/src/main/scala/org/enso/syntax/text/Parser.scala
@@ -3,9 +3,7 @@ package org.enso.syntax.text
 import java.util.UUID
 
 import cats.Foldable
-import org.enso.data.Index
 import org.enso.data.List1
-import org.enso.data.Size
 import org.enso.data.Span
 import org.enso.flexer
 import org.enso.flexer.Reader
@@ -17,6 +15,9 @@ import org.enso.syntax.text.ast.meta.Builtin
 import org.enso.syntax.text.prec.Macro
 import org.enso.syntax.text.spec.ParserDef
 import cats.implicits._
+import io.circe
+import io.circe.generic.auto._
+import io.circe.parser._
 
 ////////////////////////////////
 
@@ -346,15 +347,15 @@ class Parser {
 }
 
 object Parser {
+
   type IDMap = Seq[(Span, AST.ID)]
 
   private val newEngine = flexer.Parser.compile(ParserDef())
 
   def apply(): Parser = new Parser()
 
-  def idMap(ids: Seq[((Int, Int), AST.ID)]): IDMap = ids.map {
-    case ((ix, len), id) => (Span(Index(ix), Size(len)), id)
-  }
+  def idMapFromJson(json: String): Either[circe.Error, IDMap] =
+    decode[IDMap](json)
 
   //// Exceptions ////