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+##### LM #####
+context counting
+
+ #
+ # Regular Definitions
+ #
+ rl rl_ws /[ \t\n\r\v]+/
+ rl rl_id /[a-zA-Z_][a-zA-Z0-9_]*/
+ rl rl_num /[0-9]+/
+
+ #
+ # Tokens
+ #
+
+ lex
+ # Ignore whitespace.
+ ignore /rl_ws/
+
+ # Tokens.
+ token id /rl_id/
+ token number /rl_num/
+ end
+
+ #
+ # Global Data
+ #
+
+ target: int
+
+ #
+ # Productions
+ #
+
+
+ def get_target
+ [number]
+ {
+ match lhs [Number:number]
+ target = Number.data.atoi()
+ }
+
+ # Arbitrary item.
+ def item
+ [number]
+ | [id]
+
+ # Type definition for the count_items nonterminal.
+ def count_items
+ count: int
+
+ # List production one. The condition stops the
+ # greedy list when it has gone too far.
+ [count_items item]
+ {
+ # Pass up the data
+ lhs.count = r1.count + 1
+ if lhs.count > target {
+ reject
+ }
+ }
+
+ # List production two, the base.
+ | []
+ {
+ lhs.count = 0
+ }
+
+ # Wrapper which prevents short lists from getting through if the parser
+ # encounters an error and needs to backtrack over counted list.
+ def counted_list
+ [get_target count_items]
+ {
+ if r2.count < target {
+ reject
+ }
+ }
+
+ def start
+ [counted_list*]
+ {
+ for List:counted_list in lhs {
+ match List [Count:number Items:count_items]
+ print( 'num items: ' Count.data.atoi() '\n' )
+
+ i: int = 1
+ for Item:item in Items {
+ print( ' item ' i ': ' ^Item '\n' )
+ i = i + 1
+ }
+ }
+ }
+end # counting
+
+cons Counting: counting[]
+parse counting::start(Counting)[ stdin ]
+##### IN #####
+3 1 b c 1 1 0 3 a b c
+##### EXP #####
+num items: 3
+ item 1: 1
+ item 2: b
+ item 3: c
+num items: 1
+ item 1: 1
+num items: 0
+num items: 3
+ item 1: a
+ item 2: b
+ item 3: c