Print nested sublist extractions correctly

* PrintElmsListLevel preserves the old behaviour of PrintElmsList for
  EXPR_ELMS_LIST_LEV.
* PrintElmsList applies to EXPR_ELMS_LIST and now checks if its first
  argument is of type EXPR_ELMS_LIST or EXPR_ELMS_LIST_LEV. If yes, the
  list is put in brackets.

src/vars.c

@@ -1104,6 +1104,32 @@ static void PrintIsbList(Expr expr)
 ** Linebreaks are preferred after the '{'.
 */
 static void PrintElmsList(Expr expr)
+{
+ Expr list = READ_EXPR(expr, 0);
+ Pr("%2>", 0, 0);
+ if (TNUM_EXPR(list) == EXPR_ELMS_LIST || TNUM_EXPR(list) == EXPR_ELMS_LIST_LEV) {
+ Pr("(", 0, 0);
+ PrintExpr(list);
+ Pr(")", 0, 0);
+ } else {
+ PrintExpr(list);
+ }
+ Pr("%<{", 0, 0);
+ PrintExpr(READ_EXPR(expr, 1));
+ Pr("%<}", 0, 0);
+}
+
+
+/****************************************************************************
+**
+*F PrintElmsListLevel(<expr>) . . print a selection of several elements of a list
+**
+** 'PrintElmsListLevel' prints the list elements expression <expr> of the form
+** '<list>{<positions>}'.
+**
+** Linebreaks are preferred after the '{'.
+*/
+static void PrintElmsListLevel(Expr expr)
 {
  Pr("%2>", 0, 0);
  PrintExpr(READ_EXPR(expr, 0));
@@ -2242,7 +2268,7 @@ static Int InitKernel (
  InstallPrintExprFunc( EXPR_ELM_LIST , PrintElmList);
  InstallPrintExprFunc( EXPR_ELMS_LIST , PrintElmsList);
  InstallPrintExprFunc( EXPR_ELM_LIST_LEV , PrintElmListLevel);
- InstallPrintExprFunc( EXPR_ELMS_LIST_LEV , PrintElmsList);
+ InstallPrintExprFunc( EXPR_ELMS_LIST_LEV , PrintElmsListLevel);
  InstallPrintExprFunc( EXPR_ISB_LIST , PrintIsbList);
 
  // install executors, evaluators, and printers for matrix elements

tst/testinstall/function.tst

@@ -291,4 +291,27 @@ gap> funcloop(x -> (x in x) and x);
 function ( x ) return x in x and x; end
 gap> funcloop(x -> x in (x and x));
 function ( x ) return x in (x and x); end
+
+# nested sublist extractions
+# a single extraction
+gap> funcloop(x -> [ x ]{[ 1 ]});
+function ( x ) return [ x ]{[ 1 ]}; end
+
+# two extractions
+gap> funcloop(x -> ([ x ]{[ 1 ]}){[ 1 ]});
+function ( x ) return ([ x ]{[ 1 ]}){[ 1 ]}; end
+gap> funcloop(x -> [ [ x ] ]{[ 1 ]}{[ 1 ]});
+function ( x ) return [ [ x ] ]{[ 1 ]}{[ 1 ]}; end
+
+# three extractions
+gap> funcloop(x -> (([ x ]{[ 1 ]}){[ 1 ]}){[ 1 ]});
+function ( x ) return (([ x ]{[ 1 ]}){[ 1 ]}){[ 1 ]}; end
+gap> funcloop(x -> ([ [ x ] ]{[ 1 ]}{[ 1 ]}){[ 1 ]});
+function ( x ) return ([ [ x ] ]{[ 1 ]}{[ 1 ]}){[ 1 ]}; end
+gap> funcloop(x -> ([ [ x ] ]{[ 1 ]}){[ 1 ]}{[ 1 ]});
+function ( x ) return ([ [ x ] ]{[ 1 ]}){[ 1 ]}{[ 1 ]}; end
+
+# four extractions
+gap> funcloop(x -> ([ [ x ] ]{[ 1 ]}{[ 1 ]}){[ 1 ]}{[ 1 ]});
+function ( x ) return ([ [ x ] ]{[ 1 ]}{[ 1 ]}){[ 1 ]}{[ 1 ]}; end
 gap> STOP_TEST("function.tst", 1);