rl ident_pattern /[a-zA-Z_][a-zA-Z_0-9]*/
rl number_pattern /[0-9]+/

lex
	ignore /[ \t\n]+/
	token id /ident_pattern/
	token number /number_pattern/
end

def four_ids
	[id id id id]

B: id = construct id "b"

parse InputP: four_ids[ stdin ]
Input: four_ids = InputP.tree

for Id: id in Input {
	if ( Id == B )
		print( B '\n' )
}