lex start
{
	ignore /[\t\n ]+/
	literal '^', '|', '-', ',', ':', '!', '?', '.'
	literal '(', ')', '{', '}', '*', '&', '+'

	literal '--', ':>', ':>>', '<:', '->', '**'

	token word /[a-zA-Z_][a-zA-Z0-9_]*/
	token uint /[0-9]+/
}


def start 
	[expression]
	{
		print_xml( lhs )
	}

def expression 
	[expression '|' term]
|	[expression '&' term]
|	[expression '-' term]
|	[expression '--' term]
|	[term]

def term 
	[factor_with_rep more_term]

# Can resolve the ambiguity by making more_term shortest match.
def more_term 
	[]
|	[factor_with_rep more_term]
|	['.' factor_with_rep more_term]
|	[':>' factor_with_rep more_term]
|	[':>>' factor_with_rep more_term]
|	['<:' factor_with_rep more_term]

def factor_with_rep 
	[factor_with_rep '*']
|	[factor_with_rep '**']
|	[factor_with_rep '?']
|	[factor_with_rep '+']
|	[factor_with_rep '{' factor_rep_num '}']
|	[factor_with_rep '{' ',' factor_rep_num '}']
|	[factor_with_rep '{' factor_rep_num ',' '}']
|	[factor_with_rep '{' factor_rep_num ',' factor_rep_num '}']
|	[factor_with_neg]

def factor_rep_num 
	[uint]

def factor_with_neg 
	['!' factor_with_neg]
|	['^' factor_with_neg]
|	[factor]

def factor 
	[alphabet_num]
|	[word]
|	['(' expression ')']

def alphabet_num 
	[uint]
|	['-' uint]