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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
|
