Fix printing of empty lists, simplify printing of bigints

src/main/scala/leon/purescala/PrettyPrinter.scala

@@ -235,18 +235,18 @@ class PrettyPrinter(opts: PrinterOptions, val sb: StringBuffer = new StringBuffe
         isListLiteral(e) match {
           case Some((tpe, elems)) =>
             val chars = elems.collect{case CharLiteral(ch) => ch}
-            if (chars.length == elems.length) {
+            if (chars.length == elems.length && tpe == CharType) {
               // String literal
               val str = chars mkString ""
               val q = '"'
               p"$q$str$q"
-            }
-            
-            val elemTps = leastUpperBound(elems.map(_.getType))
-            if (elemTps == Some(tpe)) {
-              p"List($elems)"  
             } else {
-              p"List[$tpe]($elems)"  
+              val elemTps = leastUpperBound(elems.map(_.getType))
+              if (elemTps == Some(tpe)) {
+                p"List($elems)"  
+              } else {
+                p"List[$tpe]($elems)"  
+              }
             }
 
             case None =>
@@ -268,7 +268,7 @@ class PrettyPrinter(opts: PrinterOptions, val sb: StringBuffer = new StringBuffe
       case BVUMinus(expr)       => p"-$expr"
       case Equals(l,r)          => optP { p"$l == $r" }
       case IntLiteral(v)        => p"$v"
-      case InfiniteIntegerLiteral(v)        => p"BigInt($v)"
+      case InfiniteIntegerLiteral(v)        => p"$v"
       case CharLiteral(v)       => p"$v"
       case BooleanLiteral(v)    => p"$v"
       case UnitLiteral()        => p"()"

src/main/scala/leon/purescala/ScalaPrinter.scala

@@ -52,6 +52,7 @@ class ScalaPrinter(opts: PrinterOptions, sb: StringBuffer = new StringBuffer) ex
       case SetDifference(l,r)   => p"$l -- $r"
       case SetIntersection(l,r) => p"$l & $r"
       case SetCardinality(s)    => p"$s.size"
+      case InfiniteIntegerLiteral(v)        => p"BigInt($v)"
 
       case a@FiniteArray(elems, oDef, size) => {
         import ExprOps._