fixed x, added checks, enhanced doc

rpnc

@@ -106,6 +106,7 @@ my %func    = (
                    return 0;
                  }
                },
+
                '%d' => sub {
                  # percentual difference
                  if (scalar @_ == 2) {
@@ -118,6 +119,7 @@ my %func    = (
                    return 0;
                  }
                },
+
                '%+' => sub {
                  # Y + (X $ of Y)
                  if (scalar @_ == 2) {
@@ -130,6 +132,7 @@ my %func    = (
                    return 0;
                  }
                },
+
                '%-' => sub {
                  # Y - (X $ of Y)
                  if (scalar @_ == 2) {
@@ -142,6 +145,7 @@ my %func    = (
                    return 0;
                  }
                },
+
                'v' => sub {
                  if (scalar @_ == 2) {
                    my ($a, $b) = @_;
@@ -152,11 +156,13 @@ my %func    = (
                    return "$a ** (1 / 2)";
                  }
                },
+
                'pr' => sub {
                  # parallel resistance, maybe add ~/.rpncrc support
                  # where to add such custom functions...
                  return "1 / (" . join(' + ', map { "1 / $_"} @_) . ")";
                },
+
                'm' => sub {
                  # median
                  if (scalar @_ >= 2) {
@@ -175,10 +181,12 @@ my %func    = (
                    undo(); return 0;
                  }
                },
+
                'a' => sub {
                  # average
                  return "(" . join(' + ', @_) . ") / " . scalar @_;
                },
+
                # converters:
                # gallons to liters
                'tl' => sub { return $_[-1] * 3.785 },
@@ -193,6 +201,9 @@ my %func    = (
                'tmb' => sub { return $_[-1] / 1000 / 1000},
                'tgb' => sub { return $_[-1] / 1000 / 1000 / 1000 },
                'ttb' => sub { return $_[-1] / 1000 / 1000 / 1000 / 1000 },
+
+               # alias
+               'x' => sub { return join "^", @_ },
               );
 
 # math constants, always upper case letters, usable via eval{}
@@ -540,6 +551,21 @@ sub defun {
   my $code = shift;
   my ($op, $name, @tokens) = split /\s\s*/, $code;
 
+  if ($name !~ /^[a-zA-Z0-9_]+$/) {
+    print "invalid function name (a-z0-9_)!\n";
+    return;
+  }
+
+  if (grep {$name eq $_} keys %commands) {
+    print "reserved function name (command)!\n";
+    return;
+  }
+
+  if (grep {$name eq $_} keys %func) {
+    print "reserved function name (function)!\n";
+    return;
+  }
+
   $custom{$name} = "@tokens";
 
   $func{$name} = sub {
@@ -549,13 +575,14 @@ sub defun {
     # replace N1..NN with actual args
     my @body;
     foreach my $item (@tokens) {
-      if ($item =~ /^N(\d+)$/) {
-        my $i = $1;
+      if ($item =~ /^([A-Z])(\d+)$/) {
+        my $letter = $1;
+        my $i = $2;
         if ($i <= $max) {
           push @body, $args[$i-1];
         }
         else {
-          print "undefined variable N$i!\n";
+          print "undefined variable ${letter}${i}!\n";
           push @body, 0;
         }
       }