#! perl -slw
use strict;
use List::Util qw[ reduce ]; $a=$b;

our $XLATE ||= 0;

sub nestedOk{ 
	index( $_[ 0 ], '(' ) <= index( $_[ 0 ], ')' ) and
	0 == reduce{
		$a + ( $b eq '(' ) - ( $b eq ')' ) 
	} 0, split'[^()]*', $_[ 0 ] 
}

my $re_var   = qr[ [a-zA-Z]\w* ]x;
my $re_subex = qr[ \{\d+\} ]x;
my $re_func  = qr[ $re_var $re_subex ]x;
my $re_num   = qr[ -? \d+ (?: \. \d+ )? (?: [Ee] [+-]? \d+ )? ]x;
my $re_term  = qr[ $re_func | $re_subex | $re_var | $re_num ]x;
my $re_op    = qr[[,%+*/^-]];
my %ops = ( qw[ % MOD + ADD * MULT / DIV ^ POW - SUBT ] );

sub exp2rpn {
	my( $exp, $aStack, $aBits ) = @_;
	die "Unbalanced parens: '$exp'" unless nestedOk $exp;
	{
		my( $left, $op, $right, $rest ) = $exp =~ m[
			^ ( $re_term )? ( $re_op )? ( $re_term ) ( .* ) $
		]x or die "malformed (sub)expression '$exp'";
		
		for ( $left, $right ) {
			next unless $_;
			if( my( $func, $subex ) = m[^ ( $re_var )? \{ ( \d+ ) \} $]x ) {
	        	exp2rpn( $aBits->[ $subex ], $aStack, $aBits ); 
	        	push @$aStack, $func if $func 
	        }
	        else{
				push( @$aStack, $_  );
			}
		}
		push @$aStack, $XLATE ? $ops{ $op } : $op
			if $op and $op ne ',';
		$exp = $rest, redo if $rest;
	}	
	return $aStack;
}

sub parseExp {
	local $_ = $_[ 0 ];
	s[\s+][]g;
	my( $bit, @bits ) = 0;
	s[\( ( [^()]+ )  \)]{ push @bits, $1; "{${ \( $bit++ ) }}"; }ex 
          while m[[()]];
	my $toplvl = $_;
	return @{ exp2rpn $toplvl, [], \@bits };
}

die "No expression given\n" unless @ARGV;
print join', ',  parseExp $ARGV[ 0 ];

__END__
P:\test>423305-2 "2*(somevar+other) + max(this, that)"
2, somevar, other, +, *, this, that, max, +

P:\test>423305-2 "5^((-2+x)*sin(p+4)/fred)"
5, -2, x, +, p, 4, +, sin, *, fred, /, ^

P:\test>423305-2 "A+(B*C-D)/E"
A, B, C, *, D, -, +, E, /

P:\test>423305-2 "max( a, b, c, d ) * atan( pi*4, -1 )"
a, b, c, d, max, pi, 4, *, -1, atan, *

P:\test>423305 -XLATE "5^((-2+x)*sin(p+4)/fred)"
5, -2, x, ADD, p, 4, ADD, sin, MULT, fred, DIV, POW