Fix ViewString and DisplayString for ranges

... to match ViewObj and Display.

As a result, Display, PrintObj, DisplayString, PrintString and String
now all behave the same for ranges, while ViewObj and ViewString differ.
This is probably quite surprising to people, but changing it one way or
the other will affect packages, so for now let's play it safe and only
address the "obvious" bugs.

lib/list.gi

@@ -382,6 +382,34 @@ local   str,ls, i;
   return str;
 end );
 
+InstallMethod( DisplayString,
+    "for a range",
+    [ IsRange ],
+    range -> Concatenation( String( range ), "\n" ) );
+
+InstallMethod( ViewString,
+    "for a range",
+    [ IsRange ],
+    function( list )
+    local   str;
+    str := "[ ";
+    Append( str, String( list[1] ) );
+    if Length( list ) > 1 then
+      if Length(list) = 2 or list[2] - list[1] <> 1 then
+        Append( str, ", " );
+        Append( str, String( list[2] ) );
+      fi;
+      if Length(list) > 2 then
+        Append( str, " .. " );
+        Append( str, String( list[ Length( list ) ] ) );
+      fi;
+    fi;
+    Append( str, " ]" );
+    Assert(0, IsStringRep(str));
+    ConvertToStringRep( str );
+    return str;
+    end );
+
 InstallMethod( String,
     "for a range",
     [ IsRange ],
@@ -3829,7 +3857,7 @@ LIST_WITH_IDENTICAL_ENTRIES );
 ##  and in the 'ViewString' method for finite lists.
 ##
 InstallMethod( ViewObj,
-    "for finite lists",
+    "for a finite list",
     [ IsList and IsFinite ],
     {} -> RankFilter(IsList) + 1 - RankFilter(IsList and IsFinite),
 function( list )
@@ -3857,7 +3885,7 @@ function( list )
 end );
 
 InstallMethod( ViewObj,
-    "for ranges",
+    "for a range",
     [ IsList and IsFinite and IsRange ],
     function( list )
     Print( "[ " );

tst/testinstall/range.tst

@@ -40,39 +40,39 @@ gap> TestPrintRangeRep:=function(r)
 #
 gap> TestPrintRangeRep([0..1]);
 Display: [ 0 .. 1 ]
-DisplayString: <object>
+DisplayString: [ 0 .. 1 ]
 ViewObj: [ 0, 1 ]
 ViewString: [ 0, 1 ]
 PrintObj: [ 0 .. 1 ]
 PrintString: [ 0 .. 1 ]
 String: [ 0 .. 1 ]
 gap> TestPrintRangeRep([0..2]);
 Display: [ 0 .. 2 ]
-DisplayString: <object>
+DisplayString: [ 0 .. 2 ]
 ViewObj: [ 0 .. 2 ]
-ViewString: [ 0, 1, 2 ]
+ViewString: [ 0 .. 2 ]
 PrintObj: [ 0 .. 2 ]
 PrintString: [ 0 .. 2 ]
 String: [ 0 .. 2 ]
 gap> TestPrintRangeRep([0,2..4]);
 Display: [ 0, 2 .. 4 ]
-DisplayString: <object>
+DisplayString: [ 0, 2 .. 4 ]
 ViewObj: [ 0, 2 .. 4 ]
-ViewString: [ 0, 2, 4 ]
+ViewString: [ 0, 2 .. 4 ]
 PrintObj: [ 0, 2 .. 4 ]
 PrintString: [ 0, 2 .. 4 ]
 String: [ 0, 2 .. 4 ]
 gap> TestPrintRangeRep([0,-1..-2]);
 Display: [ 0, -1 .. -2 ]
-DisplayString: <object>
+DisplayString: [ 0, -1 .. -2 ]
 ViewObj: [ 0, -1 .. -2 ]
-ViewString: [ 0, -1, -2 ]
+ViewString: [ 0, -1 .. -2 ]
 PrintObj: [ 0, -1 .. -2 ]
 PrintString: [ 0, -1 .. -2 ]
 String: [ 0, -1 .. -2 ]
 gap> TestPrintRangeRep([0,-1..-1]);
 Display: [ 0, -1 .. -1 ]
-DisplayString: <object>
+DisplayString: [ 0, -1 .. -1 ]
 ViewObj: [ 0, -1 ]
 ViewString: [ 0, -1 ]
 PrintObj: [ 0, -1 .. -1 ]