Refactor Ty >> #newUndefined

This commit refactor `#newUndefined`. The implementation was temporary
and completely bogus. This commits replaces the old implementation with
new one which simply return a fresh Z3 variable of corresponding sort,
prefixed with string "undefined" to make it easier to spot.

While at it, move the method to `Sail-Jib-Interpreter` package.

Author: janvrany

src/Sail-Jib/Ty.class.st

@@ -1,9 +1,6 @@
 Class {
 	#name : #Ty,
 	#superclass : #JibProgramNode,
-	#classVars : [
-		'UndefinedValue'
-	],
 	#category : #'Sail-Jib'
 }
 
@@ -30,11 +27,6 @@ Ty class >> inducedParser [
 
 ]
 
-{ #category : #initialization }
-Ty class >> initialize [
-	UndefinedValue := '<undefined>' copy.
-]
-
 { #category : #testing }
 Ty class >> isAbstract [
 	^self == Ty
@@ -46,16 +38,13 @@ Ty >> childrenDo: aBlock [
 
 ]
 
+{ #category : #'as yet unclassified' }
+Ty >> newUndefined [
+	^ self sort mkFreshConst: 'undefined'
+]
+
 { #category : #accessing }
 Ty >> sort [
 	"Return the Z3 sort representing this (Jib) type."
 	^ self subclassResponsibility 
 ]
-
-{ #category : #'instance creation' }
-Ty >> newUndefined [
-	"Return 'undefined' value of this type. This will be the initial
-	 value before first assignment."
-	
-	^UndefinedValue "BOGUS, fix once we have type elaboration in place"
-]