fix: omit type check for defaulted optional arguments

Util.pm

@@ -22,7 +22,7 @@ BEGIN {
 }
 
 # check arguments; descriptor is string "xxx:xx" with mandatory args
-# before the :, then# optional args; x is:
+# before the :, then optional args; x is:
 #  e: any expression
 #  y: symbol
 #  p: pair
@@ -39,7 +39,7 @@ sub checkargs {
         my $argno = 0;
         my $optional = 0;
         for my $desc (split('', $descriptor)) {
-                #warn("checkargs: arglist ", &$Princs($arglist));
+                #warn("checkargs: desc $desc; arglist ", &$Princs($arglist));
                 if ($desc eq 'R') {
                         #warn("checkargs: set $desc to ", &$Princs($arglist));
                         push(@result, list2array($arglist));
@@ -51,6 +51,7 @@ sub checkargs {
                         last;
                 }
                 if ($desc eq ':') {
+                        #warn("checkargs: see :optional");
                         $optional = 1;
                         next;
                 }
@@ -59,13 +60,18 @@ sub checkargs {
                     unless $optional || consp($arglist);
                 my $arg;
                 ($arg, $arglist) = cxr($arglist);
+                #warn("\$arg: ", Dumper($arg));
+                my $optional_defaulted = 0;
                 if (defined($arg)) {
                         $argno++;
                 } else {
                         $arg = $Nil;
+                        $optional_defaulted = 1;
                 }
-                if ($desc eq 'e') {
-                        ;               # this is relatively frequent
+                if ($desc eq 'e' || $optional_defaulted) {
+                        ;               # this is relatively frequent, and we do
+                                        # not need to check the argument type
+                                        # any more
                 } elsif ($desc eq 'S') {
                         $arg = &$Princs($arg);
                 } elsif ($desc eq 'y') {