handle read errors better

Interp.pm

@@ -61,8 +61,16 @@ sub repl {
                 if ($interactive) {
                         print("> ");
                 }
-                my $expr = Read($fh);
-                last unless defined($expr);
+                my $expr = eval  {
+                        my $expr = Read($fh);
+                        return $expr;
+                };
+                if ($@) {
+                        say("Error: $@");
+                        next;
+                } elsif (!defined($expr)) {
+                        last;
+                }
 
                 if ($interactive) {
                         $value = iEval($expr);

Read.pm

@@ -25,13 +25,21 @@ my $default_input = \*STDIN;
 
 my $sepchars = quotemeta("();\n");
 
+# after a read error, consume to end of line
+sub read_error {
+        my ($in, @rest) = @_;
+        <$in>;
+        error(@rest);
+}
+
 sub Read {
         my ($in) = @_;
         $in //= $default_input;
         if (stringp($in)) {
                 my $string = $in;
                 open(my $str_in, "<", \$string) or
-                    error("read: cannot open string as filehandle: $!\n");
+                    read_error($in,
+                               "read: cannot open string as filehandle: $!\n");
                 $in = $str_in;
         }
 
@@ -42,25 +50,28 @@ sub Read {
                 my $list = read_list_elems($in);
                 return undef unless defined($list);
                 my $closer = next_token($in);
-                return error("syntax: list closed by $closer: ", $in)
+                return read_error($in, "syntax: list closed by $closer: ", $in)
                     unless $closer eq ')';
                 return $list;
         } elsif ($t eq '\'') {
                 $t = Read($in);
-                return error("EOF in quote: %s", $in) unless defined($t);
+                return read_error($in, "EOF in quote: %s", $in)
+                    unless defined($t);
                 return list(intern($Quote), $t);
         } elsif ($t eq '#\'') {
                 $t = Read($in);
-                return error("EOF in quote %s", $in) unless defined($t);
+                return read_error($in, "EOF in quote %s", $in)
+                    unless defined($t);
                 return list(intern($n_function), $t);
         } elsif ($t eq '.') {
-                return error("found . where sexpr was expected: %s", $in);
+                return read_error($in,
+                                  "found . where sexpr was expected: %s", $in);
         } elsif (symbolp($t)) {
                 return $t;
         } elsif ($t =~ m{^\"}) {
                 return substr($t, 1);
         } elsif ($t eq ')') {
-                return error("close paren unexpected");
+                return read_error($in, "close paren unexpected");
         } else {
                 return $t;
         }
@@ -77,14 +88,16 @@ sub read_list_elems {
                         push_back_token($t);
                         return $list;
                 } elsif ($t eq '.') {
-                        return error("syntax: . at start of list: %s",
+                        return read_error($in, "syntax: . at start of list: %s",
                                      $in)
                             unless $end;
                         my $sexpr = Read($in);
                         return undef unless defined($t);
                         $t = next_token($in);
-                        return error("syntax: no ) after improper list: %s",
-                                     $in)
+                        return
+                            read_error($in,
+                                       "syntax: no ) after improper list: %s",
+                                       $in)
                             unless $t eq ')';
                         rplacd($end, $sexpr);
                         push_back_token($t);
@@ -101,7 +114,7 @@ sub read_list_elems {
                         }
                 }
         }
-        return error("EOF while reading list elements: %s", $in);
+        return read_error($in, "EOF while reading list elements: %s", $in);
 }
 
 
@@ -181,23 +194,24 @@ sub symbol_or_number_or_dot {
 sub error_or_eof {
         my ($in) = @_;
         if (defined($!)) {
-                return error("read failure line $.: $!: %s", $in);
+                return read_error($in, "read failure line $.: $!: %s", $in);
         }
-        return error("unexpected EOF line $.: %s", $in);
+        return read_error($in, "unexpected EOF line $.: %s", $in);
 }
 
 sub read_macro {
         my ($in) = @_;
         #debug("read macro");
         my $c = next_nonwhite($in);
-        return error("unexpected EOF line $.: %s", $in) unless defined($c);
+        return read_error($in, "unexpected EOF line $.: %s", $in)
+            unless defined($c);
         if ($c eq '\'') {
                 my $result = '#\'';
                 #debug("read macro returns %s", $result);
                 return $result;
         # and possibly more
         } else {
-                return error("unknown reader macro \"#$c\": %s", $in);
+                return read_error($in, "unknown reader macro \"#$c\": %s", $in);
         }
 }