Add type checks to Concatenation

In particular, this lets the undefined expression `Concatenation( [ 1 ] )` throw an error instead of returning `1`.
gap-system · Mar 29, 2023 · 1f6de1c · 1f6de1c
1 parent a78e3d2
commit 1f6de1c
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/lib/list.gi b/lib/list.gi
@@ -2084,8 +2084,14 @@ InstallGlobalFunction( Concatenation, function ( arg )
     if Length( arg ) = 0  then
         return [  ];
     fi;
+    if not IsList( arg[1] ) then
+        Error( "Concatenation: arguments must be lists" );
+    fi;
     res := ShallowCopy( arg[1] );
     for i  in [ 2 .. Length( arg ) ]  do
+        if not IsList( arg[i] ) then
+            Error( "Concatenation: arguments must be lists" );
+        fi;
         Append( res, arg[i] );
     od;
     return res;